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STATUS OF THE BALD EAGLEIN BRITISH COLUMBIA
byD.A. Blood
andG.G. Anweiler
Wildlife BranchMinistry of Environment, Lands & Parks
Victoria, B.C.
Wildlife Working Report No. WR-62
February 1994
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STATUS OF THE BALD EAGLEIN BRITISH COLUMBIA
byD.A. Blood
andG.G. Anweiler
Wildlife Branch
Ministry of Environment, Lands and Parks
Victoria, B.C.
Wildlife Working Report No. WR-62
February 1994
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"Wildlife Working Reports frequently contain preliminary data, soconclusions based on these may be subject to change. Working Reports re-ceive little review. They may be cited in publications, but theirmanuscript status should be noted. Copies may be obtained, dependingupon supply, from the Ministry of Environment, Lands and Parks,Wildlife Branch, 780 Blanshard Street, Victoria, B.C., V8V 1X4."
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FORWARD
In cases where a Wildlife Working Report is also a Species' Status Report, it may contain arecommended status for the species by the author. This recommendation is the opinion of the authorand may not necessarily reflect that of the Wildlife Branch.
Official designations will be made by the Wildlife Branch in consultation with experts, and the datacontained in the Status Report will be considered during the evaluation process.
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TABLE OF CONTENTS
SUMMARY ......................................................................................................................................... ix
1.0 GENERAL BIOLOGY ................................................................................................................. 1
1.1 Reproduction ........................................................................................................................... 1
1.1.1 Breeding age and frequency........................................................................................ 1
1.1.2 Timing of reproductive events .................................................................................... 2
1.1.3 Nest dispersion ............................................................................................................. 2
1.1.4 Productivity .................................................................................................................. 3
1.2 Population Structure ............................................................................................................... 4
1.3 Mortality/Survival Rates ........................................................................................................ 6
1.3.1 Nestlings ....................................................................................................................... 6
1.3.2 Subadults ...................................................................................................................... 6
1.3.3 Adults ............................................................................................................................ 6
1.4 Movements and Seasonal Concentrations ............................................................................ 7
1.4.1 Movements ................................................................................................................... 7
1.4.2 Seasonal concentrations ............................................................................................ 10
1.5 Behaviour and Adaptability ................................................................................................. 11
1.5.1 Food habits ................................................................................................................. 11
1.5.2 Nesting habits ............................................................................................................. 12
1.5.3 Roosting behaviour .................................................................................................... 13
1.5.4 Disturbance................................................................................................................. 13
1.5.5 Adaptability to human-caused habitat change ......................................................... 14
1.5.6 Vulnerability to severe natural events ...................................................................... 15
2.0 HABITAT ..................................................................................................................................... 16
2.l Habitat Characteristics ......................................................................................................... 16
2.1.1 North America ............................................................................................................ 16
2.1.2 British Columbia ........................................................................................................ 18
2.1.3 Food Resources .......................................................................................................... 28
2.2 Habitat Impacts and Trends ................................................................................................. 35
2.2.1 Removal of nest trees ................................................................................................ 35
2.2.2 Removal of perching and roosting trees .................................................................. 37
2.2.3 Contamination of food sources ................................................................................. 37
2.2.4 Loss of foraging habitat ............................................................................................ 38
2.2.5 Human competition for food ..................................................................................... 38
2.2.6 Regional impacts in British Columbia ..................................................................... 38
2.2.7 Habitat trends ............................................................................................................. 44
2.2.8 Habitat status and protection .................................................................................... 45
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3.0 DISTRIBUTION ......................................................................................................................... 45
3.l North America ...................................................................................................................... 45
3.1.1 Breeding range ........................................................................................................... 45
3.1.2 Winter distribution ..................................................................................................... 45
3.2 Canada ................................................................................................................................... 46
3.2.1 Breeding range ............................................................................................................ 46
3.2.2 Winter distribution ....................................................................................................... 46
3.3 British Columbia ................................................................................................................... 46
3.3.1 Breeding range ........................................................................................................... 46
3.3.2 Winter distribution ....................................................................................................... 50
4.0 POPULATION SIZE AND TRENDS ......................................................................................... 50
4.1 North America ....................................................................................................................... 50
4.1.1 Population size ............................................................................................................ 50
4.1.2 Population trends ......................................................................................................... 50
4.2 British Columbia ................................................................................................................... 52
4.2.1 Population size ............................................................................................................ 52
4.2.2 Population trends ......................................................................................................... 53
5.0 LEGAL PROTECTION ............................................................................................................... 54
5.1 United States .......................................................................................................................... 54
5.2 Canada ................................................................................................................................... 55
5.3 British Columbia ................................................................................................................... 55
6.0 LIMITING FACTORS ................................................................................................................. 55
6.l Causes of Regional Population Declines .............................................................................. 55
6.2 Direct Mortality ..................................................................................................................... 56
6.2.1 Natural mortality ......................................................................................................... 56
6.2.2 Human-caused mortality ............................................................................................. 56
6.3 Reproductive Failure ............................................................................................................. 57
6.4 Disturbance ............................................................................................................................ 57
6.5 Limiting Factors .................................................................................................................... 58
6.5.1 Food resources ............................................................................................................. 58
6.5.2 Nesting sites ................................................................................................................ 58
7.0 SPECIAL SIGNIFICANCE OF THE SPECIES ......................................................................... 58
7.1 Status...................................................................................................................................... 58
7.2 Public Interest ........................................................................................................................ 59
7.3 Economic Value ..................................................................................................................... 59
7.4 Species Security ..................................................................................................................... 59
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8.0 PROTECTION AND MANAGEMENT ...................................................................................... 60
8.1 Inventory Needs ..................................................................................................................... 60
8.2 Protection Needs .................................................................................................................... 60
8.2.1 Habitat protection ........................................................................................................ 60
8.2.2 Eagle protection ........................................................................................................... 61
8.3 Research Needs ..................................................................................................................... 62
9.0 EVALUATION ............................................................................................................................. 63
10.0 LITERATURE CITED................................................................................................................. 64
11.0 ACKNOWLEDGEMENTS ......................................................................................................... 73
APPENDICES ...................................................................................................................... 75
LIST OF TABLES
Table 1. Nesting success of Bald Eagles in British Columbia and nearby
areas in recent years ............................................................................................................... 4
Table 2. The relationship between Bald Eagle productivity and population
trends in North America......................................................................................................... 5
Table 3. The proportion of immature age-classes in stable or increasing
Bald Eagle populations in northwestern North America ...................................................... 6
Table 4. Distribution and importance of Bald Eagle nesting and winter
habitat in British Columbia.................................................................................................. 21
Table 5. Estimated relative importance of ecoprovinces, and biogeoclimatic
zones within them, for providing Bald Eagle nesting and wintering habitat ...................... 24
Table 6. Regional variation in tree species used for nesting by Bald Eagles
in British Columbia .............................................................................................................. 26
Table 7. Some characteristics of Bald Eagle nest trees in British Columbia .................................... 27
Table 8. Food habit observations for Bald Eagles in coastal British Columbia ............................... 31
Table 9. Food habit observations and inferences for Bald Eagles in the Interior
of British Columbia ............................................................................................................. 34
Table 10. Linear frequency of adult Bald Eagles and eagle nests along
shorelines in British Columbia ............................................................................................ 49
Table 11. Estimates of the abundance of adult and immature Bald Eagles
in British Columbia during the nesting season ................................................................... 53
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LIST OF FIGURES
Figure 1. Seasonal occurrence of nonbreeding Bald Eagles, and of eggs
and nestlings in British Columbia ........................................................................................ 2
Figure 2. Hypothetical movement patterns of Bald Eagles in the
Pacific Northwest ................................................................................................................. 9
Figure 3. Major Ecoregion subdivisions of British Columbia .......................................................... 20
Figure 4. The breeding and wintering distribution of Bald Eagles in Canada ................................. 47
Figure 5. The distribution and relative abundance of nesting Bald Eagles
in British Columbia ............................................................................................................ 48
Figure 6. Distribution and relative abundance of wintering Bald Eagles
in British Columbia ............................................................................................................ 51
LIST OF APPENDICES
Appendix 1. Reproductive terminology .............................................................................. 75Appendix 2. The number of Bald Eagles counted on Christmas bird counts
in British Columbia, December 1973 through December 1988 .............. 76
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SUMMARY
I. GENERAL BIOLOGY
i. Reproduction
The Bald Eagle (Haliaeetus leucocephalus) is alarge bird with delayed maturation, small clutchsize, and long lifespan. Though capable of breed-ing at 4 years of age, many do not nestuntil they are 6 or 7 years old. Only one clutch israised per year, and in saturated populations, alarge proportion of the adults do not breed everyyear.
Bald Eagles nest earlier in the season thanmost other birds in the same area. In BritishColumbia, egg laying varies from late February/early March on the south coast to about mid-April in the northern Interior. The incubationperiod is about 35 days. Young remain in the nestfor l0 to 13 weeks, and may frequent the nest sitefor several additional weeks. Young may fledgefrom nests as early as the end of June on thesouth coast and as late as late August in thenorthern Interior.
Bald Eagles are territorial during the nestingperiod. Although active nests may be as little as500 m apart, the average distance between activenests in good coastal habitat is about 3 to 4 km.Nesting eagles cannot be expected to crowd intoscattered remnants of old growth as shoreline for-ests are clear-cut.
Nest records for British Columbia indicate that63% of clutches had 2 eggs, 31% had l egg, and6% had 3 eggs. Based on a few studies in thesouthern part of the province, nesting successwas 62% to 91% in recent years, and the numberof young fledged per occupied site varied from0.9 to l.5. These statistics are similar to those foradjacent jurisdictions and suggest that eaglepopulations here are stable or increasing. How-ever, survival rates of adults and the percentageof adults that do not successfully nest, statistics
which are not generally available, may be moreimportant in maintaining eagle populations thanthe productivity of the adults that do breed.
ii. Population Structure
Sex ratios are not available for either juvenile oradult eagles. Immature eagles make up 35% to41% of the population in British Columbia inmid-winter, suggesting a normal rate of repro-duction and juvenile survival.
iii. Mortality and Survival Rates
Mortality between egg and fledging stages isabout 40% to 50%, and only 5% to 20% offledged young reach breeding age. The annualmortality rate of adults has been estimated at 5%.In the wild, eagles have been known to live atleast 27 years.
iv. Movements and Seasonal Concentrations
Bald Eagles that nest in interior British Columbiaand across the boreal forest of Canada migratesouth into the United States for the winter.Major wintering areas of those birds are alongthe Mississippi and Missouri rivers and otherrivers in the west, where they concentrate atmany reservoirs and National Wildlife Refuges.Many eagles that nest on the British Columbiacoast make late-summer movements to south-east Alaska or the interior of B.C. where earlysalmon runs occur, and then return to the BritishColumbia Coast for the winter. Salmon spawningstreams are the major concentration areas fromlate autumn to mid-winter. In spring, concentra-tions are often associated with staging andspawning herring and with eulachon runs. Minorsummer concentrations occur at food sources,such as seabird colonies and places where tidalcurrents bring hake to the surface. Eagles move agreat deal to take advantage of seasonal foodsources.
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v. Behaviour and Adaptability
Food habits — The Bald Eagle is one of themost versatile birds in North America, with re-spect to its food habits. Fish make up the bulk ofthe annual diet in most areas; however, seabirds,waterfowl, and intertidal invertebrates may beof high seasonal importance, and such diverseitems as gull eggs, Chukar Partridge, rabbits,hares, and Muskrats are taken where locallyabundant. Much of the above food is obtained ascarrion; however, apparently healthy fish, birds,and mammals are captured. Large mammals,such as dead livestock; ungulates killed by traffic,wolves or severe weather; and beached whales orsea lions, are important foods. Bald Eagles haveadapted to many food sources made available byhumans.
Nesting habits — Nests are almost always indominant old-growth trees near saltwater orfreshwater shorelines. Many tree species, bothconiferous and deciduous, are used. Two ormore alternative nests may occur in a breedingterritory, but eagles normally use the same nestfor several years in succession. Being dependenton large, hence old, trees located near an abun-dant food source, Bald Eagles are somewhatspecialized in their nesting habits. They cannotbe expected to adapt to second-growth nest treesor to nest far from shorelines.
Roosting behaviour — In winter, BaldEagles typically use communal night roosts inlarge coniferous or deciduous trees. These areusually near food concentrations; however,eagles will fly up to 30 km to roost. Theimportance of roosts for eagle survival has notbeen conclusively demonstrated.
Disturbance — Although chronic distur-bance may result in disuse of some otherwisesuitable habitats, continued nesting in settledareas suggests considerable tolerance of humanactivity. However, frequent flushing of eaglesfrom feeding sites, particularly in winter, isexpected to have adverse bioenergetic conse-quences.
Adaptability to human-caused habitatchange — Bald Eagles are relatively tolerant ofland use changes surrounding their nest sites,but, of course, cannot adapt to a complete loss ofold-growth trees. Eagles are not expected to bevery adaptable to adverse impacts on their foodresources; however, documentation of such ef-fects is lacking. Eagles have respondedfavourably to human-caused habitat changes thathave enhanced forage resources.
Vulnerability to severe natural events —Local populations may sometimes suffer set-backs from natural events like severe storms;however, the species as a whole is not particu-larly vulnerable.
II. HABITAT
i. Habitat Characteristics
North America — The main components ofBald Eagle nesting habitat throughout NorthAmerica are large trees for nest sites and huntingperches in proximity to relatively extensiveaquatic habitats, preferably shallow waters, andan abundant supply of food in the form of fishor aquatic birds. On treeless offshore islands,nesting may occur on the ground. Open water isthe most important component of winter habitat,since this provides access to the major winterfoods: fish and waterfowl. Nocturnal roost treesare also important in winter. Diurnal perchesadjacent to food sources are important at allseasons.
British Columbia — Nesting season habitatconsists of large, usually old, nest trees plusadjacent aquatic foraging habitat. Best habitatsare along the seacoast, especially at or nearestuaries and broad intertidal zones, island andreef complexes, seabird colonies, and sites withstrong tidal currents. Most important Interiornesting habitats are along large low-gradient riv-ers with high floodplain/wetland development,and at low elevation lakes and wetland com-plexes of the Interior Plateau. At least 13 species
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of nest trees are used in British Columbia;Sitka spruce, Douglas-fir, western redcedar,cottonwood, and aspen are the most frequent.These are dominant or co-dominant specimensin the nest vicinity - often gnarled and very old.Mean distances of nests from shorelines in vari-ous study areas varied from 24 m to 173 m.Distances appear to be greatest where thenearshore area is most developed. Nests occur inextensive old-growth stands, fragmented old-growth parcels, and lone veteran trees in secondgrowth or slash. The nest tree environments varyfrom remote wilderness to urban landscapes.
Winter foraging habitat on the coast includesthe intertidal zone, salmon and eulachon spawn-ing streams, herring staging/spawning sites, andestuaries with waterfowl concentration. In the In-terior, large southern lakes with wintering cootsand diving ducks, rivers below power dams, andlow-elevation ungulate ranges are the usual win-ter habitats. On the coast, old-growth conifersand/or cottonwoods provide communal nightroosts near some concentrated food sources.
ii. Habitat Impacts and Trends
Removal of nest trees is mostly attributable tologging; however, clearing for settlement, agri-culture, and other purposes also contributes to theimpact. Linear developments like highways,powerlines, and pipelines often follow valley bot-toms or parallel rivers, further reducing the stockof nest trees. Hydro dams have flooded habitat insome areas. The same factors also threaten diur-nal perches and night roosts. Industrial pollutantsare a potential threat through contamination ofeagle foods. Shoreline development may inhibiteagle foraging in some areas. Excessive harvestof eagle foods by humans could also have an ad-verse impact on eagle populations.
Significant, permanent reduction of nestingpopulations has probably only occurred in urbanareas like Greater Vancouver and Victoria, butnesting habitat loss is accelerating on southeastVancouver Island, the Gulf Islands, and in the
Fraser Valley. In those areas the current rate ofchange is at least moderate and of concern be-cause the losses are permanent. Nesting habitat isalso changing rapidly in coastal areas subject toclear-cut logging; however, this is of less concernbecause logging companies are starting to inven-tory for nests before logging and, therefore, nesttrees are often spared, many sites are non-oper-able, and, as a last resort, some second-growthtrees can be allowed to advance to old-growthstatus. Impacts on feeding habitat have probablybeen significant only in the Georgia Depression,and even there the current rate of degradationwould be rated as slow.
About 90% of British Columbia’s Bald Eaglesnest on Crown lands, where government couldinstitute programs to control logging impacts onnesting populations. Probably less than l0% ofnest sites are in protected areas such as parks orEcological Reserves. Nest tree protection is pres-ently not adequate on either Crown or privateland. Most critical habitat, particularly on Crownlands, can probably be protected by means otherthan land acquisition. Some land acquisitionwould be desirable in the Georgia Depression,but waterfront lands here are very expensive.
III. DISTRIBUTION
i. North America
Nesting is widespread in North America, occur-ring from the Aleutian Islands to Newfoundland,and south to California, Arizona, and Florida.Major wintering areas are the Pacific Coast fromAlaska to Oregon, and major river valleys of thecentral and western United States.
ii. Canada
Bald Eagles nest across boreal Canada north tothe tree line, and south to the U.S. border. Excep-tions include the treeless prairies and urbanizedareas. Most Canadian nesting populations outsideB.C. winter in the U.S.
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iii. British Columbia
The nesting range includes the whole provinceexcept for alpine/subalpine zones. Over 90% ofeagles wintering here are on the coast; the re-mainder occur at scattered southern Interior sites,especially large lakes and ice-free rivers.
IV. POPULATION SIZE AND TRENDS
i. North America
The continental population of about 70,000 birdsis stable or increasing in most areas, but the geo-graphic range is gradually shrinking in heavilydeveloped parts of the U.S. and southern Canada.
ii. British Columbia
The nesting season population is estimated atabout 21,000 birds, including immatures (28%),non-breeding adults (30%), and nesting adults(42%), but excluding nestlings. The winterpopulation is estimated at 20,000 to 30,000 birds,of which 35%-40% are immatures. Populationsin most regions are stable because the habitat issaturated. Declines in nesting abundance haveprobably occurred in heavily settled areas such assoutheast Vancouver Island, Greater Vancouver,and the lower Fraser Valley, and may be continu-ing.
V. LEGAL PROTECTION
In the United States, the Bald Eagle is protectedfederally by the Bald Eagle Protection Act,Endangered Species Act, and various State laws.It is listed as Endangered or Threatened in all ofthe lower 48 states. The Endangered Species Actincludes provisions for habitat protection.
In Canada, the species has no direct federalprotection, but direct killing and harassment isillegal under provincial and territorial statutes.Bald Eagles are listed as Endangered in Ontarioand New Brunswick.
In British Columbia, no legislation exists to pro-tect potential nest or roost trees on lands outsideof parks or related reserves; however, actual nesttrees are protected, whether or not they are occu-pied. It is the policy of both the ministries ofForests and Environment, Lands and Parks todesignate “wildlife trees” and protect them fromcutting.
VI. LIMITING FACTORS
i. Causes of Regional Population Declines
Bounty hunting in Alaska up to l950, and pesti-cide contamination in eastern North Americaprior to l970, caused significant declines, butpopulations in many areas have largely recov-ered. Pesticide residue (DDT) is still hamperingrecovery in some areas, such as southernCalifornia (R. Davies, pers. comm.). Habitat losshas been going on for 200 years and has affectedpopulations in southern Canada and the UnitedStates.
ii. Direct Mortality
Natural mortality factors and rates in wild eaglesare poorly known. Important human-related mor-tality factors in British Columbia are collisionswith vehicles and structures, poisoning, electro-cution, shooting, trapping, plumage fouling, andaccidents such as entanglement in nets or fences.The proportion of the population affected is notknown, but eagles appear to be maintaining theirnumbers in the face of such losses.
iii. Reproductive Failure
This is not a problem in British Columbia, al-though monitoring of pollutants such as dioxinsand furans is needed.
iv. Disturbance
Human disturbance may adversely affect a fewnesting or wintering eagles in localized areas in
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the province, but is not felt to be a significantlimiting factor. However, this may be of greaterconcern in the future.
v. Limiting Factors
Loss of nest trees to date has probably had aminor impact on the nesting season carryingcapacity of British Columbia for Bald Eagles,however local reductions are expected to haveoccurred and further declines are expected. Theavailability of food, together with the territorialnature of nesting eagles, is felt to be the majorfactor presently limiting population increase.
VII. SPECIAL SIGNIFICANCE OF THE SPECIES
Although listed as Threatened or Endangeredacross much of its geographic range, the bulk ofthe population occurs in Alaska, British Colum-bia, and the Canadian boreal forest, locationswhere populations and habitats are quite secure.Public interest in the species is very high becauseof a general fascination with large raptors, andbecause this one is the national bird of the UnitedStates. Predation impacts by Bald Eagles are oflittle economic concern. Nature tours featuringBald Eagles have much economic potential inBritish Columbia and elsewhere.
VIII. PROTECTION AND MANAGEMENT
i. Inventory Needs
A province-wide inventory of nest trees and com-munal roosts is needed in order to protect thesehabitat requirements.
ii. Protection Needs
Recent changes to the Wildlife Act have provideda formal provincial policy, backed by regulation,that is providing needed protection of nest treesin British Columbia. On private lands, a public
information program aimed at land owners/man-agers is the most urgent need. Protection fromdegradation and pollution of buffer areas aroundnest trees, key forage resources, and habitats isalso needed.
Reduction of direct mortality could be achievedby province-wide elimination of lead shot, dis-continued use of some pesticides, movement ofungulate carcasses away from road edges, modi-fied design of power lines, reduced use ofleg-hold traps and snares, increased enforcementwhere shooting is a problem, and increased sup-port of rehabilitation programs. Areas whereprotection from human disturbance is requiredneed to be identified and managed accordingly.
iii. Research Needs
The following research needs are discussed:
l. Assessment of forest practices in relationto nesting abundance
2. Assessment of mortality rates and causes3. Monitor contaminants in eagles and their
food4. Evaluation of eagle movement patterns5. Assess tolerance of nesting eagles to
human civilization6. Determine rates of non-breeding by
adults
IX. EVALUATION
The Bald Eagle should be removed from the pro-vincial Blue List and placed on the Yellow List. Ifcriteria were applied on a regional basis, the spe-cies might warrant Blue-list status in the GeorgiaDepression Ecoprovince1. Localized declines innesting status will probably occur unless moreeffort is made to preserve known and potentialnest trees.
1 Ed. Note: The current (1993) edition of the Provincial Blue List includes the Bald Eagle.
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1.0 GENERAL BIOLOGY
1.1 Reproduction
The basic elements of Bald Eagle reproduc-tive biology have been known for some time(Bent l937), and have been recently summa-rized by several authors (Snow l973; Beebel974; Brownell and Oldham l983; Gerrardand Bortolotti l988). Parameters such asbreeding age and clutch size are quite simi-lar throughout the species range, however,seasonal timing of events varies greatly withlatitude, elevation, and continentality. Mostreproductive information is from studiesdone outside British Columbia, but informa-tion for this province is introduced for com-parative purposes when available. Campbellet al. (l990) summarize Bald Eagle breedinginformation for British Columbia.
1.1.1 Breeding age and frequency
The Bald Eagle is a large bird with delayedmaturation, small clutch size, and longlifespan. The species undergoes a prolongedmaturation process, with correspondingplumage changes from the all-dark plumageof the first year bird to the white head andtail of the mature eagle, essentially obtainedwhen four years old (Bortolotti l984). BaldEagles are capable of breeding at four yearsof age and, in areas where populations aredepressed and vacant habitat is available,they do so; however, in stable populationswhere most territories are already occupied,most Bald Eagles may not mate or breed un-til six years old or older (Gerrard andBortolotti l988).
There is little information on how long ea-gles live in the wild or on how long they re-main productive. A female, recaptured inAlaska at the age of 21 years and ll months,
was breeding (Cain l986). The oldest knownage of a wild eagle is 27 years (Evans l982).In captivity, eagles have lived to 50 years(Snow l973).
Many authors have stated that eagles remainmated for life and occupy the same nestingterritory for many years (Retfalvi l965;Robards and King l966, Brown and Amadonl968). Recent work with colour-marked ea-gles in Saskatchewan has tended to supportthis, although it was also suggested thatsome adults may remate following a failednesting attempt (Gerrard and Bortolottil988). In Alaska, three adults were observedattending one nest; the same behaviour wasobserved at one nest in Maine (Fraser et al.l983).
Bald Eagles are capable of producing onlyone brood per year. The first set of eggs maybe replaced if lost early in incubation (Bentl937). The frequency with which pairs repro-duce is not well documented, but many nestsare active year after year and it is possiblethat under optimal conditions most pairs willattempt reproduction annually. However, inmost populations studied, a number of pairseither fail early in the incubation process orfail to breed at all. The factors that determinewhether or not a pair attempts reproductionare not well understood, although weather,disturbance, availability of food, and the out-come of the previous year’s nesting attempthave all been suggested as possible factors(Gerrard and Bortolotti l988). In some years,up to 86% of the adults in southeast Alaskadid not breed (Hansen and Hodges l985). InSaskatchewan, about 40% of the populationin an average year was made up of breedingadults, 20% consisted of adults not associ-ated with nests, and the remainder were im-mature birds (Gerrard and Bortolotti l988).These percentages suggest that where the
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breeding habitat is fully occupied, manyadult eagles do not nest every year.
1.1.2 Timing of reproductive events
Major events in the reproductive cycle ofBald Eagles include courtship and nest repair,egg laying, incubation, care of young in thenest, fledging of young, and post-fledging as-sociation of young with the nest site. In total,these activities may encompass six months ormore. Where food is available in winter,adults may be seen at or near their nests atany time of the year. Bald Eagles nest earlierin the season than most other birds occurringin the same area (Figure 1).
Territorial defence and courtship may starttwo or three months before eggs are laid. Re-habilitation of established nests occurs everyyear. The number of days taken for egg lay-ing is not explicitly stated in the literature,but Gerrard and Bortolotti (l988) state thateggs are laid “... a few days apart.” Incuba-tion is reported to take 33-36 days (Herrickl932; Newton l979); up to 40 days has alsobeen suggested (Beebe l974). Young remainin the nest for l0-ll weeks on average, but insome cases up to 13 weeks (Gerrard et al.l974; Newton l979). The young often remain
in the vicinity of the nest for a month or moreafter fledging, sometimes returning to it(Gerrard et al. l974).
For British Columbia as a whole, dates forll8 egg clutches varied from 12 February to27 June, with 50% recorded between 20April and 12 May; dates for 425 broods were30 March to l September, with 52% between22 June and 12 July (Campbell et al. l990;Figure 1). Egg laying is earliest on the southcoast (mid-February onward, but primarilyearly March), somewhat later on the northcoast and southern Interior (mostly lateMarch to early April) and later still in thenorthern Interior or anywhere in the Interiorat high elevations. Young may fledge fromlate June to late August, depending on loca-tion. In the Yellowstone area in the U.S.,Swenson et al. (l986) found a breeding chro-nology difference of l month associated withan elevational difference of 765 m. As onemoves north in British Columbia, eaglesreturn to the breeding areas progressivelylater; Campbell et al. (l990) give arrival datesat the nest as follows: Fort St. John, 24 Feb.;Williams Lake, 29 Feb.; Prince George, 14March; Atlin, l April. In southwest Yukon, thefirst eagles returned to the nest sites in lateMarch (Blood and Anweiler l990a).
1.1.3 Nest dispersion
Regional nesting densities vary greatly, butare highest where food is most abundantduring the brood-rearing period. However,Bald Eagles are territorial during the nestingperiod and will nest only so close together.Breeding eagles defend territories of l.5 km2
to 6.0 km2 (Broley l947), but will forage out-side of the defended zone. In areas of discon-tinuous habitat, nests may be widelydispersed, but this is not a function of territo-riality.
Figure 1. Seasonal occurrence ofnonbreed-ing Bald Eagles, and of egg and nestlings,in British Columbia. (From Campbell et al.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
nonbreeding
eggs
nestlings
Nonbreeding and Breeding Chronology
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Mean nesting densities along shorelines inareas of high eagle abundance are about lnest per 3 km to 4 km (Hodges l982), how-ever, minimum observed distances betweenactive nests are less than this, i.e., 650 m atAdmiralty Island, Alaska (Robards and Kingl966) and 500 m near Nanaimo (Bloodl989a). Mahaffy and Frenzel (l987), by ob-serving responses to decoys, determined theaverage defended distance from active neststo be 600 m.
The territorial nature of Bald Eagles is of sig-nificance for conservation planning in areaswhere old-growth forest is being lost. In suchareas, nesting eagles cannot be expected tocrowd into remaining forest fragments.Rather, the carrying capacity is reduced inproportion to the amount of habitat lost.
1.1.4 Productivity
Reproductive terminology followsPostupalsky (l974) and Swenson et al. (l986);definitions are given in Appendix l. The nor-mal clutch size is two eggs, although l- and3-egg clutches are also common (Bent l937;Snow l973). In Saskatchewan, 74% ofclutches were 2-egg, 24% were 3-egg andonly 3% were l-egg. For British Columbia,Campbell et al. (l990) reported on ll8clutches; 63% contained 2 eggs, 31% con-tained l egg and 6% contained 3 eggs.
One or two young are the normal production,although three young are also fledged fromsome nests (Gerrard and Bortolotti l988;Blood and Anweiler l990a). Campbell et al.(l990) reported the size of 425 British Co-lumbia broods of various ages as follows: lyoung 60%; 2 young 37%; 3 young 3%.These figures do not provide a direct estimateof productivity because many broods werenot at the fledging stage.
Many Bald Eagle nest surveys have been car-ried out in British Columbia to assess distri-bution and abundance, however, there havebeen few studies from which the commonlyused indices of success - the number of occu-pied sites producing young to fledging ageand number of young fledged per occupiedsite - can be calculated. Obtaining such statis-tics requires an early survey to determine thenumber of nest sites occupied by adult pairs,and a late survey to record the number ofsites having near-fledged young and the totalnumber of fledglings present. A single surveyjust prior to fledging can indicate the numberof young per successful nest, but this is not aparticularly useful statistic because thenumber of unsuccessful breeding attempts isnot known.
Available productivity data for BritishColumbia and nearby areas are given inTable l. They indicate that breeding successhere is similar to and within the range of thatin adjacent areas. Data on the relationship be-tween Bald Eagle productivity and popula-tion trends is given in Table 2. The provincialproductivity statistics in Table l indicate thatour populations should be in the stable or in-creasing categories. Sprunt et al. (1973)stated that for an eagle population to remainstable, at least 50% of the pairs occupyingterritories must breed and an average of 0.7young must be produced per pair. However,Swensen et al. (l986) determined that a popu-lation in the Yellowstone Unit of the GreaterYellowstone Ecosystem (in the Western U.S.)did not meet those criteria, and yet was con-sidered stable (Table 2). It has also beenstressed by Grier (l980) that the survival ratesof adults and the percentage of adults that donot successfully nest may be more importantin maintaining populations of long-livedbirds like eagles than the productivity of theadults that do breed.
4
Table l. Nesting success of Bald Eagles in British Columbia and nearby areas in recent years.
No. of 1 Nest 2
Location occupied success Productivity3
territories (%)
Young Young fledged/ fledged/
occupied site successful site
BRITISH COLUMBIAGulf Islands (Sprunt l969) l75 73 ? ?Nanaimo area (Blood l989a) 53 62 0.9 l.5Fraser Valley (Dunbar l988) 32 84 1.5 l.7S.E. B.C. (Forbes and Kaiser l984) ll 91 1.4 1.5Nechako R. (Blood and Anweiler 1983) ? ? ? 1.4
ADJACENT AREASS.W. Yukon (Blood and Anweiler l990) 39 72 1.1 1.5Wash. State (McAllister et al. l986) 144 66 0.9 1.4Idaho (Forbes and Kaiser l984) 35 ? 1.1 l.8Montana (Forbes and Kaiser l984) 71 ? 1.4 l.9
1 may include cumulative observation in the same area for >1 year.2 % of occupied nest sites producing young to fledging age.3 an occupied nest has paired adults present early in the nesting season; a successful site produces at least one young to
fledging age.
1.2 Population Structure
Although criteria have been developed to dif-ferentiate the sexes of both adult and nestlingeagles based on external morphology(Bortolotti l984a,b), these are not readilyused in the field and sex ratio data for wildpopulations are not available.
Ratios of adult to immature eagles, based onpresence or absence of the white head andtail, may be quite variable due to differentialsightability and movements. Ratios may varygreatly from place to place and season to sea-son. However, some data are available fromintensive studies over fairly large areas andprovide an indication of normal conditions.
In summer, when nestlings and subadults areincluded together as immatures, the imma-ture proportion in inland areas is about 50%(Table 3). Based on Amchitka Island data(Sherrod et al. l976), the proportion may belower on the coast; however, differential dis-tribution may be involved. Normal early au-tumn immature proportions appear to be inthe 40% to 50% range, and mid-winter pro-portions in the 30% to 40% range (Table 3).During a period of pesticide-induced popula-tion decline in eastern North America inthe l960s, the immature proportion droppedfrom 37% to 23% at Hawk Mountain, Penn-sylvania (Sprunt l969), and as low as 6% inIllinois (Southern l963).
5
Table 2. The relationship between Bald Eagle productivity and population trends in NorthAmerica.1
Area Product- Nest Population Study Source
ivity3 success (%)4 trend period
Continental Unit, GYE 1.22 68 Increasing l976-82 Swenson et al. (l986)
Besnard Lake, Saskatchewan l.l7 73 Stable l968-81 Gerrard et al. (l983)
Snake Unit, GYE l.06 67 Increasing l976-82 Swenson et al.(l986)
Wisconsin l.00 66 Stable l962-70 Sprunt et al.(l973)
Kodiak Island, Alaska l.00 63 Stable l963-70 Sprunt et al.(l973)
Greater Yellowstone 0.98 60 Increasing l976-82 Swenson et al. Ecosystem (l986)
Amchitka Island, Alaska 0.86 60 Increasing l969-84 Sherrod et al.(l976)
San Juan Islands, Wash. 0.84 62 Stable l975-80 Grubb et al.(l983)
Arizona 0.80 49 Stable l975-80 Grubb et al.(l983)
Everglades, Florida 0.73 50 Stable l961-70 Sprunt et al.(l973)
Yellowstone Unit, GYE 0.53 34 Stable l976-82 Swenson et al.(l986)
Michigan 0.52 37 Declining l96l-70 Sprunt et al.(l973)
Maine 0.35 26 Declining l962-70 Sprunt et al.(l973)
Great Lakes shores 0.14 l0 Declining l961-70 Sprunt et al.(l973)
1 Table from Swenson et al. 1986.2 GYE = Greater Yellowstone Ecosystem.3 Based on occupied nests.4 Based on occupied nests.
Although summer data are lacking for BritishColumbia, the winter age-ratio data (Table 3)are for a large segment of the winteringpopulation in which immature and adult
eagles are thought to be well mixed. Therange of 35% to 41% immatures suggeststhat reproduction and juvenile survival ratesare normal in this population.
6
Table 3. The proportion of immature age-classes in stable or increasing Bald Eagle populationsin northwestern North America.
Percent immature
Location Season Nestlings Subadult Total Source
Northern Saskatchewan Summer l8 33 51 Leighton et al. l979
Greater Yellowstone Autumn 23 21 44 Swenson et al. l986 Ecosystem
Nooksack River, Winter 32-36 Stalmaster et al. l979 Washington
Southwestern B.C. Winter l986 35 Farr and Dunbar l986Winter l987 35 Farr and Dunbar l987Winter l988 37 Farr and Dunbar l988Winter l989 40 Farr and Dunbar l990Winter l990 41 Dickie l990
1.3 Mortality/Survival Rates
1.3.1 Nestlings
Hodges (l982) calculated the survival rate ofnestlings in southeast Alaska to be 0.57 be-tween 8 June and 6 August. Blood andAnweiler (l990a) suggested a loss of 50% be-tween the egg and fledging stages in south-west Yukon. In northern Saskatchewan,Gerrard and Bortolotti (l988) found thatabout 8% of eggs laid did not hatch, that onenestling in 3-nestling clutches usually did notsurvive, and that some nestling losses oc-curred when nests fell out of trees. Most nes-tling mortality apparently occurs in the firstweek or two after hatching.
1.3.2 Subadults
Gerrard et al. (l978) calculated survival ratesfor the first three years of life for two samplesof Saskatchewan Bald Eagles; a colour-marked population, and a population consist-ing of all eagles banded in Saskatchewan.
Survival rates for the colour-marked samplewere 37% at the end of the first calendaryear, 22% at the end of the second year, andl9% at the end of the third year. For thebanded population, survival rates were 53%,26%, and 20%, respectively. Brown andAmadon (l968) also published survival ratesfor banded eagles; their figures for the sametime periods were 21%, 9%, and 4%.Sherrod et al. (l976) estimated that total mor-tality of immature eagles prior to breedingwas about 90%.
1.3.3 Adults
Mortality or survival rates for adult BaldEagles are poorly known, because few havebeen banded to date. On Amchitka Island,Sherrod et al. (l976) estimated that annualmortality of adults was 5.4%. Additional in-formation on subadult and adult survival ratesis needed. Grier (l980) has stressed that thepopulation dynamics of Bald Eaglesappear to hinge more on survival than on re-production, yet our knowledge “... is concen-
7
trated on reproduction with almost no infor-mation on survival.” Fraser (l985) also pointsout that for proper assessment of populationtrends, natality, mortality, immigration, andemigration rates should be measured. Thishas not yet been accomplished for any BaldEagle population.
1.4 Movements and SeasonalConcentrations
1.4.1 Movements
Continental population — The seasonalmovements of Bald Eagles are among themost complex of any bird (Beebe l974;Gerrard and Bortolotti l988). Seasonal move-ments vary from population to population,depending on geographic location, weather,food availability, age and status of the birds,and other factors.
In coastal and other temperate areas, adultsmay be largely non-migratory while the non-breeding or immature members of the samepopulation may undertake long movements(Hodges et al. l987). Eagles from Florida areknown to summer as far north as the Mari-time Provinces, after the Florida breedingperiod (Gerrard and Bortolotti l988).
Populations breeding in northern interiorNorth America undertake long distancemovements into the southern United States,where they winter before returning to breed-ing areas in early spring. Eagles may winterfurther south than usual during severe win-ters, and a few may occasionally winter farnorth of the usual wintering areas. Adultstend to depart later and return earlier thanyoung birds, and immatures tend to move far-ther than adults. Even among immatures, theyoungest birds move earlier and farther thanthe older ones. Some populations move north
after breeding, while others move south.Even on the breeding areas, age determinesmobility. Breeding adults confine themselvesto small territories, while non-breedingadults, and immatures in particular, maywander widely (Gerrard and Bortolotti l988).While many individuals from one area maymove to the same wintering and breeding ar-eas over a period of years, others from thesame population may wander widely. Al-though some young eagles from Saskatch-ewan were found to move to the same winterarea along the Missouri River over a periodof several years, and to return to their lake oforigin for the summer, others have beenfound as far as the Great Lakes, Texas, Cali-fornia, and even southeast Alaska (Gerrardand Bortolotti l988).
The large-scale and more traditional move-ments of non-coastal populations can besummarized as follows: populations breedingin the Great Lakes area and Ontario movesouth to winter mainly along the MississippiRiver drainage; populations from westernManitoba and Saskatchewan move south towinter across the midwestern and centralstates, mainly along the Missouri River drain-age; and populations from Alberta and Mac-kenzie, and possibly interior BritishColumbia, move into the interior westernstates (Gerrard l983). These birds move southin late fall (October-November) and return inearly spring (March-April) (Spencer l976;Millsap l986; Gerrard l983).
Pacific Northwest populations — Move-ments of eagles in the Pacific Northwest arestill poorly known, particularly the move-ments of inland populations (Beebe l974;Hodges et al. l987; Campbell et al. l990).Although eagles that breed at the coast do notundertake migrations of continental magni-tude, they do move locally; immature birds in
8
particular engage in complex, long-distancemovements. Populations in the interior aremore migratory, being forced south from thebreeding grounds by severe winter weather.
Although no part of the British Columbiacoast is devoid of eagles at any time (Beebel974), numbers in many areas fluctuategreatly at different seasons, and large num-bers can be found congregating wherever fishor aquatic bird concentrations occur. Move-ments of eagles along the coast are largely aresponse to these seasonal food concentra-tions (Beebe l974; Servheen and Englishl979; Campbell et al. l990).
There is a rather abrupt and large-scaledeparture from the south coast of BritishColumbia in late summer, and at this time(August-September) areas such as the GulfIslands may be almost devoid of eagles(Hancock l964; G. Anweiler, pers. comm.). Itis thought that these birds move north as faras Alaska to take advantage of salmonspawning runs that peak there in mid-August.Servheen and English (l979) proposed a hy-pothetical late summer and early fall disper-sal from the south coast of British Columbiaand adjacent Washington in two directions,north to southeast Alaska and northwest overthe mountains or up river valleys to salmonspawning rivers in Interior British Columbia(Figure 2). Eagles from the north coast andInterior begin to return to the south coast inlate October, and spend most of the winterthere (Hancock l964; Campbell et al. l990).Adults return earliest, then immatures.Servheen and English (l979) proposed tworoutes for eagles returning to the south coastof B.C. in late fall: one south along the coastfrom southeast Alaska, joined by birds mov-ing from the Interior west to the coast, and amovement back down the major river sys-
tems southwest to the coast (Figure 2).Hodges et al. (l987), by means of radio te-lemetry, showed that this southward move-ment down the coast does involve some birdsfrom Alaska, but found no evidence of amovement from interior British Columbia tosoutheast Alaska. They did note that a nes-tling banded at Whitehorse, Yukon, wasfound the following winter on the OlympicPeninsula of Washington.
On the south coast of British Columbia, peaknumbers occur in December and January,largely in response to availability of salmoncarcasses along rivers (Farr l988; Farr andDunbar l988; Teske l989). In late winter andearly spring, many of these birds disperse toother coastal food concentrations, such asstaging and spawning herring and eulachonruns.
Based on observations of colour-markedeagles, Servheen and English (l979) pro-posed that there are two general migrationroutes for the Skagit wintering population.The first route is over the mountains in anorth and northeast direction toward interiorBritish Columbia. The second route is downthe Skagit Valley to the west, then norththrough Puget Sound and the Strait of Geor-gia. Birds wintering in the Lower Mainlandarea may have a similar spring pattern, butthis remains to be confirmed.
Movements of populations in interior BritishColumbia appear to be similar to those ofeagles that nest east of the Rockies, with thebirds moving south in late fall and returningto their breeding areas in early spring. Eaglesbegin to appear in the Okanagan Valleyin early December, building to a peak inFebruary and March; they begin to dispersein late March, and by mid-April all but the
9
Figure 2. Hypothetical movement patterns of Bald Eagles in the Pacific Northwest. (FromServheen and English 1979).
Hypothetical movement patterns of Bald Eagles during August and September in the Pacific Northwest.
Hypothetical movement patterns of Bald Eagles during October, November, and December in thePacific Northwest.
10
local breeding population has departed(Cannings et al. l987). Earliest dates of ar-rival back at some interior British Columbianesting sites are as follows: Lumby, 22 Feb-ruary; Prince George, 14 March; Atlin, 1April (Campbell et al. l990). Arrival of springmigrants in the Peace River area, l983-l989,has varied from 4 to 24 April, with a mean ofl5 April (Siddle l990). In southwest Yukon,eagles return to their nest sites in late Marchand April (Blood and Anweiler l990a). InWashington State, along the Columbia River,wintering eagles begin to arrive in late Octo-ber, with numbers increasing to a peak in thethird week of February; all have departed bythe middle of April (Knight et al. l979).
The above review indicates that part of theBritish Columbia Bald Eagle population is aninternational one. This is based largely on themarking of small numbers of birds in Alaskaand Washington, and requires further investi-gation.
eagles may feed at a unique late spawningrun of salmon (Cline l982; Hodges et al.l987). Eagles also concentrate at inland siteswhere fish spawn. Each fall, up to l000 stopto feed on spawning kokanee in Glacier Na-tional Park, Montana (McClelland l973).Wintering Bald Eagles also congregate atmany reservoirs and dams in the northern andcentral United States, as well as NationalWildlife Refuges, where they are attracted bythe abundance of fish killed by turbines oroxygen depletion, or by large numbers ofwintering waterfowl. (Snow l973; Griffin etal. l982).
Millsap (l986) stated that the largest concen-trations of wintering eagles in the UnitedStates were found along the major riversystems, in particular the Missouri and Mis-sissippi, but also along most other systemsin the west. Sites where wintering concentra-tions of eagles were found were mapped forNorth America by Spencer (l976).
Smaller seasonal concentrations of eaglesmay be found wherever food, particularlycarrion, is available, such as at garbagedumps, lambing areas, and seabird colonies.
British Columbia — Bald Eagles alsoconcentrate seasonally at many sites of foodabundance in British Columbia. These aredescribed in Section 2.0 Habitat. Most sea-sonal concentrations are along rivers or in themarine environment, both of which receivesome protection under the Fisheries Act(Canada) and other legislation. Many othersites of concentration, such as large seabirdcolonies, have been given EcologicalReserve status.
1.4.2 Seasonal Concentrations
North American population — Whennesting, eagles tend to be dispersed through-out the breeding habitat, but at other seasonsthey may be highly sociable and gather inlarge numbers where food is abundant. Win-tering eagles will also roost communally andseveral hundred may gather to roost at night.Even during the breeding season, large num-bers of non-breeding adult and immature ea-gles may gather at seasonal sources ofabundant food.
By far the largest and best known concentra-tion of Bald Eagles occurs each fall on theChilkat River in Alaska, where up to 4,000
11
under-represented in the food remains re-ported at nests because fish remains are muchless persistent or obvious than are remains ofbirds and mammals, and because fish bonesare digested by Bald Eagles and may not ap-pear in castings (Steenhof l976). In foodchoice studies, Bald Eagles invariably chosefish over birds and mammals when offeredall three (Wright l953). Bald Eagles have alsobeen observed to switch from mammalianand avian prey, even in the nest, when fishwere available (Retfalvi l970; Griffin et al.l982). Many different species of fish are re-corded from Bald Eagle diets, ranging fromlarge salmon and dogfish on the coast, tosmelt, suckers, and trout. Whatever fish areavailable and obtainable will usually betaken. A large portion of the fish taken maybe scavenged, although eagles do takehealthy fish, including salmon, when theycan.
The second most important food of BaldEagles at all seasons appears to be waterfowland seabirds of all types. These may be takenas dead or crippled birds, but eagles also pur-sue and capture a wide variety of apparentlyhealthy waterfowl, and have even been ob-served successfully hunting and capturingbirds as large and agile as Common Loons.Eagles often nest in proximity to seabirdcolonies, which make up the bulk of their dietas long as they are available. This has beennoted on both the Pacific and Atlantic coasts.Seabird eggs are also eaten. BaldEagles also prey on Great Blue Heron colo-nies, and have been cited as the major causeof failure for some colonies. Wintering eaglesare attracted to many National WildlifeRefuges across the United States, in particu-lar to the large numbers of crippled and deadwaterfowl found in these areas (Griffin et al.l982). Wherever they occur, coots appear tobe a favoured prey of Bald Eagles, especially
1.5 Behaviour and Adaptability
1.5.1 Food habits
The diet of Bald Eagles is restricted to animalmatter, but the range of animals consumed isextremely broad, ranging from marine inver-tebrates, such as crab and shellfish, to mam-mals, including seals, whales and livestockcarrion. The diet can be grouped into threemajor categories: fish, aquatic birds, and car-rion of all types. Bald Eagles are opportunistsand shift quickly from one food to another asit becomes available. Large numbers willcongregate to take advantage of seasonallyabundant foods.
The methods of obtaining food, summed upby Beebe (l974), indicate the remarkable ver-satility of this species:
"To a singular degree the Bald Eagle emu-lates the behaviour and hunting techniques ofevery other kind of raptorial bird on thecontinent, but is has also developed a trickor two of its own. Bald Eagles are variously(depending on circumstances and individualfood preferences) scavengers, carrion-feeders, pirates, fishermen, mammal or birdpredators, and they capture the latter eitherfrom the air, on the ground, or from thewater.”
Adults are more adept at taking live prey thanare immature birds. The immatures are moredependent on carrion, and along with thenon-breeding adults, are more mobile andbetter able to take advantage of local or sea-sonal abundances.
Throughout its range, the main prey of theBald Eagle is fish, and in many areas, 90% ormore of the Bald Eagle annual diet is com-posed of fish (Oberholser l906). Fish may be
12
in winter, possibly because of their relativeease of capture (Bent l937; Snow l973).
Carrion of all sorts, including dead fish,road-killed mammals, dead waterfowl andgarbage, are important Bald Eagle foods. Asnoted previously, salmon carcasses are amajor food of eagles wintering along thewest coast, and dead waterfowl and winter-killed fish are important on wildlife refugesin the United States. Ungulate carrion isimportant in many mountainous areas(Swenson et al. l986). Locally, items such asdomestic sheep carrion and road killed rab-bits may be seasonally important (Hancockl965; Retfalvi l970). On Amchitka Island,Alaska, Sherrod et al. (l976) found that eaglenumbers increased with the opening of thegarbage dump. It is possible that the bulk ofeagle food is scavenged, and that many preyitems recorded at nest studies were picked upas carrion.
Though commonly associated with aquaticenvironments, Bald Eagles have been shownto prey heavily on jackrabbits and ChukarPartridge in dry upland areas in winter (Plattl976; Fielder l982). On California’s ChannelIslands, they have been recorded as takinglive piglets and young goats (R. Davies, pers.comm.), further evidence of the versatility ofthis species.
Food habits data for British Columbia aregiven in Tables 8 & 9 in Section 2.
1.5.2 Nesting habits
Although Bald Eagle nests have been foundin a variety of sites, including the ground onoffshore sea stacks and islands, cliffs, andrelatively small trees, eagles usually placetheir nests in the tallest old-growth treesfound in the areas where they are nesting. In
most regions of the continent, old-growthtrees may be a prerequisite for Bald Eagles tonest successfully (Beebe l974).
Bald Eagles tend to repair and reuse the samenest for many years, and their nests may be-come as large as those of any bird in theworld (Beebe l974). Often, more than onenest is built in a breeding territory, with alter-nate nests being used in different years. Asmany as four nests may occur in one territory,although not more than one is active in agiven year (Isaacs et al. l983). Nests falldown with some regularity, and may be re-built, often in the same tree. In Alaska, about5% of the nests were lost annually, and inSaskatchewan, about l0% were lost eachyear, with nests lasting on average 5 years; inother locations, a single nest may last for dec-ades (Bent l937; Hodges l982; Gerrard andBortolotti l988).
The species of tree used varies greatly fromregion to region, and even within regions.Both live and dead coniferous and deciduoustrees are used. Usually the tallest suitable old-growth trees in the area are selected. This isbased on structure rather than species(Anthony et al. l982). Important factorsidentified in the selection of nest trees wereenumerated by Snow (l973) as: a clear flightpath to a point on a beach or river, an openview of the surrounding area, and proximityto water and a food source. Gerrard andBortolotti (l988) found that eagles needed tobe able to approach the nest from more thanone direction, depending on wind direction.Burke (l983) stressed that nest trees had to bestrong enough to support the large nest overtime and prominent enough to provide acommanding view.
Nests are rarely placed more than a few hun-dred metres from shore in wilderness areas,
13
although in areas of human activity, eaglesmay respond by nesting away from shore-lines (Gerrard et al. l975). Few nests are lo-cated more than l.6 km from water.
The effects of human disturbance on nest siteselection have not been clearly identified(Snow l973). In many areas, eagles haveavoided nesting where human activity takesplace; in other areas, they may continue to doso or may respond by relocating nests furtherback from the shoreline. Beebe (l974) statedthat in areas where human activity occurred,tall nest trees were probably a prerequisitefor eagles to feel secure. This suggests thateagles may be more tolerant of human activ-ity where tall trees, like veteran Douglas-firs,are available than in locations where onlysmaller ones, like aspen and lodgepole pine,occur.
Opportunities for eagles to nest on theground are extremely restricted. Populationmaintenance is dependent upon availabilityof large trees capable of supporting heavynests and provide freedom from human dis-turbance and ground predators. In this sense,the Bald Eagle has rather specialized nestinghabitat needs. It cannot be expected to adaptto nesting in second-growth trees, or to relo-cate nests many kilometres away from feed-ing areas.
Additional details on nest site selection andnesting environments in British Columbia aregiven in Section 2.
1.5.3 Roosting behaviour
Wintering Bald Eagles typically use commu-nal night roosts, and there is some evidencethat there is a group identity associated withthe various roosts. In the Pacific Northwest,up to 400 Bald Eagles are known to gather at
some roosts (Anthony et al. l982). Roosts areinvariably located in the vicinity of largeaggregations of prey, such as spawningsalmon or wintering waterfowl, and the loca-tion may shift according to weather, preymovements, or disturbance (Snow l973;Keister and Anthony l983). Eagles may movelong distances between the nearest suitableroost and the feeding area, in some instancesup to 28 km. Typically, they choose the clos-est suitable trees, usually old-growth coniferstands, which provide protection from windand rain and generally have more favourablemicro-climates than surrounding areas(Keister and Anthony l983).
During harsh weather, eagles may remain inthe roost all day (Waste l982). Along theNooksak River in Washington State, eaglesspent 67.5% of the day in the roosts and usedconifer stands even though mature deciduoustrees were closer, perhaps because the coni-fers offered greater shelter. By roosting in theconifers they saved up to 5% of their dailyenergy budget, even after accounting for theextra energy expended in flying farther(Stalmaster and Gessaman l984). Eagles mayalso follow each other from roosts, whichmay facilitate food-finding in times of short-ages (Knight and Knight l983).
1.5.4 Disturbance
The impacts of human disturbance on BaldEagles, either during the breeding or winter-ing periods, are still being argued. Manyfactors are involved, including the kinds andduration of disturbance, the period in theseasonal life cycle when disturbance occurs,previous conditioning of the birds, age of thebirds, and the amount of direct versus indi-rect disturbance. However, disturbance hasbeen identified as a major concern in manyareas where eagles occur.
14
As pointed out by Fraser (l985), “.... while anumber of observers have attributed loweredproductivity and even territorial abandonmentto human disturbances, ... others have foundlittle or no evidence of disturbance-causednest failures.” He goes on to state that the ef-fect of human disturbance on wintering ea-gles has also been equivocal, and that whilemodelling studies and theoretical considera-tions have suggested potential populationconsequences of disturbing wintering eagles,no actual changes have yet been documented.
What does seem fairly clear is that chronicdisturbance results in disuse of areas by BaldEagles. Fraser (l985) concluded that :
“Human activities which chronically exceedthe limits of eagle tolerance may be consid-ered a form of habitat destruction. This is aparticularly insidious impact because there isno overt indication of the impact obvious tountrained or casual observers.”
Beebe (l974) noted some adaptability ofnesting eagles with respect to human activityat nest sites, as follows:
“In wilderness situations, Bald Eagles aregreatly disturbed by human intrusion intotheir territories, but also they show a high de-gree of adaptability and tolerance if the hu-man activity is not directed toward them.”
He reports that in places where nesting eaglessee humans afoot or in vehicles regularly,they become excited only when the nest treeis climbed, and that:
“Their sensitivity to human intrusion is...conditioned by the degree to which the adultsare exposed to human activity.”
Human invasion of the nest itself during in-cubation normally causes abandonment ofthe eggs, and the birds do not renest in thesame season. A similar invasion when youngare in the nest is usually tolerated and theyoung are not deserted. Beebe (1974) sug-gested that this type of disturbance may beremembered and result in the abandonmentof the nest after the young are flying, and therelocation of the pair in a new nest some dis-tance away the year following (Beebe l974).However, five years of eagle chick captureson Vancouver Island (for transplant to Cali-fornia) did not result in any abandonment orrelocation activity (R. Davies, pers. comm.).
Continued nesting by Bald Eagles in settledareas (Blood l989b) suggests considerabletolerance of human activities. Young eaglesraised in nests overlooking subdivisions andother developments are expected to acceptsimilar nest sites when of breeding age,provided that a secure nest tree and adjacentforaging areas remain. Bald Eagles are long-lived and capable of learning that humanpresence is not necessarily a threat. Humanactivities that displace eagles from criticalfeeding areas, for example water-skiing onsmall lakes or travel along salmon spawningstreams in winter, may be of some long-termconcern.
1.5.5 Adaptability to human-causedhabitat change
Like any living thing, Bald Eagles cannot beexpected to adapt to complete loss of criticalhabitat, such as old-growth nest trees orimportant foraging sites. Whenever theseresources disappear, the habitat will be va-cant. However, eagles show tolerance forsome degree of habitat change.
15
Nesting habitat — Bald Eagles do notrequire extensive wilderness or old-growthforest for nesting. Scattered old-growth treesin large stands of second growth are readilyused for nesting (Hodges et al. l984). Pairswill continue to nest in small patches of oldgrowth, in lone trees left standing in loggedclear-cuts, and in trees surrounded by subdi-visions or adjacent to industrial activity.However, long-term acceptability of suchsites has not been studied. Mathisen (l968)found that habitat modified by timber man-agement in the immediate vicinity of nestsites did not appear to affect nesting activity.In some areas, nesting eagles have apparentlyabandoned shorelines used for cottage devel-opment (Gerrard and Bortolotti l988), or haveresponded by nesting further away fromshorelines (Fraser l985). However, this maybe a response to direct disturbance, such asnoise and human activity, rather than to habi-tat change. It seems that the nature of the up-land landscape surrounding nest trees isrelatively unimportant for nesting eagles aslong as secure nest trees are available anddisturbance levels are not excessive.
Foraging habitat — Bald Eagles are notexpected to be very adaptable to negative im-pacts on their foraging habitat. Although suchimpacts have undoubtedly occurred, they arepoorly documented. On the other hand, thisspecies has shown much adaptability infinding and using foraging habitats and foodresources made available by humans. Thedistribution of Bald Eagles wintering in thelower 48 states has been greatly altered in thepast 50 years by the creation of dams, reser-voirs, and waterfowl refuges along the majorriver systems (Evans l982; Snow l973). Ea-gles now concentrate at these ice-free areaswhere an abundance of fish, waterfowl, and
carrion is available (Evans l982; Griffin et al.l982). Eagles have also been found concen-trating at areas where a seasonal abundanceof food has been created as a result of live-stock production (Hancock l964), garbagedumps (Sherrod et al. l976), or the introduc-tion of wildlife such as feral rabbits (Retfalvil970), Chukar (Feilder l982), and kokaneesalmon (Snow l973).
Although eagles have shown an ability toadapt to many changes in habitat, and insome cases these are considered to be favour-able, they must be evaluated with caution.For example, the creation of dams and reser-voirs may have created new and valuablewinter habitat at the expense of riparian habi-tat, which was capable of supporting nestingeagles. The assumption that such changes area net benefit for eagles cannot be entirelysupported (Fisher and Hartman l983).
1.5.6 Vulnerability to severe naturalevents
Bald Eagles are relatively widespread, nu-merous, mobile, and adaptable birds, andtherefore not unduly vulnerable as a speciesto severe natural events. However, localpopulations may from time to time suffer set-backs from natural events.
Extensive wildfires may destroy nests orcause adults to abandon nests. Blood andAnweiler (Unpubl.) believed that the reasoneagles were absent as a breeding bird along areach of the Rancheria River on the Yukon/British Columbia border was because poten-tial nesting trees had all been removed bywildfire. Bald Eagles are largely dependenton wetlands for food, consequently, foodsupplies are relatively unaffected by fire.
16
Severe storms may blow down nests and nesttrees, both during the time they are active andbetween nesting seasons. This may also af-fect nesting in the following year, as wasobserved in Florida following nest lossesfrom a hurricane (Broley l947). Severe winteror spring weather may result in mortality toeagles, particularly immature eagles whomay already be stressed by food shortages.Severe spring storms were believed to beresponsible for a widespread reduction ineagle productivity in Saskatchewan (Gerrardand Bortolotti l988). Spring storms may alsocause eagles to abandon nests, resulting inegg and nestling losses (Evans l982).
2.0 HABITAT
2.1 Habitat Characteristics
2.1.1 North America
Nesting habitat — Bald Eagle nestinghabitat embraces the Florida Everglades andthe Aleutian Islands, arid Arizona and therain-drenched northwest Pacific coast; arange of climatic and biotic conditions towhich few North American birds are adapted.As noted by Beebe (l974):
“Bald Eagles are not restricted to any onehabitat or climatic zone. Their hunting hab-its, food, and even reproductive period haveevolved to suit extremely diverse situations.Over their entire range, Bald Eagles areclosely associated with water and largetrees.”
In spite of their dependence on trees forroosting, nest sites, and hunting perches, BaldEagles are not woodland birds. Their hugewingspan prevents them from being able tofly in any but the most open woods, conse-quently, their use of forested areas is more or
less restricted to using the largest trees alongthe forest edge, or those treetops that pro-trude above the canopy.
The main components required for nestinghabitat are large trees for nest sites and hunt-ing perches, closely associated with relativelyextensive aquatic habitats, preferably shallowwaters, and an abundant supply of food in theform of fish or aquatic birds. On treeless off-shore islands, nesting may occur on theground, usually on cliffs or steep slopes.Rarely, cliffs or rock pinnacles are used in in-land areas. Anthony et al. (l982) describedBald Eagle breeding habitat in the PacificNorthwest as primarily occurring in theponderosa pine, mixed conifer, Douglas-fir,and Sitka spruce/western hemlock foresttypes. Some nesting also occurs in riparianwoodlands, mainly along large river systemsin the Interior, where nests are usually placedin cottonwoods. Most nests are locatedwithin l.6 km of large waterbodies, usuallylakes, reservoirs, large rivers, or coastal estu-aries. Old-growth ponderosa pine, Douglas-fir, Sitka spruce and western hemlock are theusual nest trees. Trees with a diameter breastheight (DBH) of less than 76 cm are rarelyused. Where nesting in undisturbed forests, acomponent of old growth is invariablypresent. Nest trees are the dominant or co-dominant individuals in the forest stand andare selected for structure, and not by species.
In southeast Alaska, Hodges and Robards(l982) reported that nesting eagles were de-pendent on old-growth stands near the wa-ter’s edge. They described the ideal nest treeas follows:
“The ideal nest is located probably on aprominent point or islet exposed to a broadchannel, or narrow passage if tidal currentsare present. The nest tree is a large, old-
17
growth Sitka spruce or western hemlock, withmassive limbs in the upper crown, usually theresult of a deformity, a broken top or a bushytop. The nest is high in the tree, with a com-manding view over the water and easy accessto the eagle on the wing.”
Bangs et al. (l982) state that throughout thebreeding range of Bald Eagles, nest trees aretypically “
... close to water, have a clear view to water,are usually the oldest and largest living mem-bers of the dominant overstory, and oftenprovide some type of sparse cover above thenest.”
On the Kenai National Wildlife Refuge inAlaska, they found most nests in ripariancottonwoods that were less than 200 m fromwater, and observed that eagles tended to se-lect sites along slow-moving, clear streamsthat were used by spawning salmon in falland spawning trout in spring; and sites nearclear, fish-producing lakes.
In the Tanana River area in interior Alaska,Richie (l98l) found most nests in deciduoustrees (cottonwood and aspen) in a variety ofwoodland types. Over 70% were in poplar ormixed poplar/spruce forest, with 94% inliving trees. He stated that distance to ice-freewaterbodies early in the nesting period mayhave been a critical factor in determining nestsite locations.
In Oregon, Isaacs et al. (l983) found 85% ofnests to be within l.6 km of majorwaterbodies, with one as far as 7 km away.Ninety-five percent of the nests were indominant or co-dominant ponderosa pine,Douglas-fir, and Sitka spruce.
In northern Saskatchewan and Manitoba,Gerrard et al. (l975) found that eagles pre-ferred to nest within 200 m of large lakes andrivers in large aspens more than 21.5 m tall.Nests near spawning streams that were openin early spring had the highest productivity.A considerable number of the nests found atsmall lakes were within 3.2 km of largelakes, and the presence of the larger lakeswas an important factor in eagles being ableto nest by smaller waterbodies. A preferencewas also found for island nest sites.
Detailed analysis of nest habitat in the PacificNorthwest is presented by Anthony et al.(l982). Hodges and Robards (l98l) providesimilar information for Alaska.
Winter habitat — The term “winter” isused here to refer generally to the non-nest-ing season, that is fall, winter, and earlyspring, and includes habitats used by migrat-ing eagles. Open water has been identified asthe most important component of winterhabitat (Brown and Amadon l968; Snowl973; Steenhof l978), but the supply of foodthat is found at open water areas is the criticalfactor. Large numbers of wintering eaglesmay also occur in arid valleys of the westernU.S. where carrion or jackrabbits are avail-able (Murphy l975). In most regions, eagleswinter where there are abundant fish orwaterfowl concentrations.
l. Food supply
In late fall and early winter, most eaglesalong the west coast are found concentratedalong salmon spawning streams. In late win-ter and early spring, eagles may shift to takeadvantage of other fish, such as spawningherring or eulachons. Throughout interiorNorth America, eagles winter wherever open
18
water occurs; in many areas waterfowl con-centrations provide the food base, and thelarge numbers of crippled and dead water-fowl found around National WaterfowlRefuges attracts many wintering eagles(Steenhof l978). Coots are also an importantfood for many inland populations of winter-ing eagles. Below dams and along certain riv-ers, fish are the main winter food.
2. Perching and roosting habitat
Diurnal perches are an important componentof winter habitat because they allow surveil-lance of potential prey with a minimum ofenergy expenditure. Proximity to a foodsource has been demonstrated to be the mostimportant factor influencing perch site selec-tion (Steenhof l978; Stalmaster and Newmanl979). Although eagles perch on a wide rangeof substrates, trees are the preferred sites, andeagles consistently use certain trees and evencertain branches on the tree. As much as 75-83% of the daylight hours may be spent on aperch (Steenhof l978). Most perches borderopen areas and provide a good view of thesurrounding habitat. Exposure to the sun mayalso be important by helping to reduce heatloss. Favoured perch trees tend to be tall andstout; both live and dead trees are used. Spe-cies of tree varies from region to region, withcertain species preferred in different areas;location and structure appear to be more im-portant than species (Steenhof l978).
Wintering eagles frequently roost commu-nally at night, with up to 400 eagles sharing asingle site (Anthony et al. l982). Night roostsmay be located some distance from feedingareas; in the Klamath Basin they were foundto be as much as l6 km from feeding areas,and changed as the distribution of waterfowlchanged. In Utah, eagles were observed toroost 28.7 km from the nearest feeding area.
Most roosts are well protected from the wind,and locations may change according toweather. Roosts tend to be located in the larg-est trees available and may vary from a singletree to a stand several hectares in size. Manyare used year after year. Both dead and livetrees are used, and tree selection is apparentlybased more on structure than on species.Anthony et al. (l982) found that PacificNorthwest roosts were invariably located inforest stands that had at least a remnant ofold-growth; stands were variable in speciescomposition, area, and tree size, but the old-growth component provided the roost trees.In Washington State, Stalmaster andGessaman (l984) found that along theNooksack River coniferous trees were pre-ferred, and that conifers provided shelter thatwas thermally superior to that offered by de-ciduous trees. Detailed analysis of roost sitecharacteristics is provided by Anthony et al.(l982) for the Pacific Northwest and bySteenhof (l978) for the general range of theBald Eagle.
2.1.2 British Columbia
Nesting habitat
l. General features
Bald Eagle nesting requirements in BritishColumbia, as elsewhere, consist of large treesfor nest support, and adjacent aquatic foodsources. This habitat occurs at low elevationsalong the entire coast, and along major riversand around lakes or wetland complexes in theInterior, particularly the Southern and CentralInterior. These productive lowlands are pre-cisely the area where most of British Colum-bia’s human population is concentrated, aswell as much forest harvesting and landclearing for agricultural and other purposes.
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An exception to the requirement for treesoccurs in a few very limited locations, suchas Triangle Island, off the north end of Van-couver Island, where an abundance of food,together with freedom from land predatorsand human disturbance, allows ground-nest-ing (Vermeer et al. l976).
Campbell et al. (l990) described the locationof Bald Eagle nests in B.C. as follows:
“On the coast, most nests (65%; n =543) were near the seashore, on islands, inestuaries, and at the mouths of rivers andcreeks. Other nests sites on the coast in-cluded lakeshores, marshes, sloughs, la-goons, and rivers. In the interior, nests werefound along lakeshores (58%; n = 87), on is-lands in rivers and lakes (22%), and on riverbanks (16%) also being important. Othernests were located at the mouths of creeks,along railway tracks, and on hillsides.”
Suitable nest trees occur across most of theprovince; however, nesting abundance is notrandom, but strongly associated with food re-sources that are abundant and available dur-ing the nesting season. The most extensiveand productive nesting habitats are along thecoast where fish, aquatic birds, and intertidalinvertebrates are abundant. The best coastalnesting habitats usually have one or more ofthe following features:
- high shoreline length per unit areadue to many islands, channels orinlets;
- a broad intertidal zone and/or manyoffshore reefs exposed at low tide;
- presence of estuaries or mudflats;- proximity to strong tidal currents;- regularly used herring spawning
habitats nearby;
- seabird or Great Blue Heron nestingcolonies in the vicinity.
Habitats such as steep-sided fjords are lesssuitable. In the coastal zone, Bald Eagles alsonest around lakes and along rivers, but inlower densities than along the seacoast. Thisis undoubtedly because food resources areless abundant. Floodplains of major riverslike the Fraser and Skeena, where not seri-ously modified by humans, appear to providethe best non-marine coastal nesting habitat(Dunbar l988). Almost all coastal nestinghabitat, even along rivers and around lakes, iswithin a few hundred metres of sea level.
In the B.C. Interior, nests most commonlyoccur along medium to large rivers character-ized by low gradient, a sinuous channel, andextensive floodplain development; aroundlakes and reservoirs of various sizes, particu-larly low-elevation lakes with good fishpopulations; and where many small lakes orwetlands occur in proximity (Blood andAnweiler unpubl.; Forbes and Kaiser l984).The best Interior nesting habitats are in thesouthern valley and central plateaus, althoughnesting occurs north into the Yukon. Allknown nests in the Interior are below 1370 melevation (Campbell et al. l990).
2. Habitat distribution
As noted in the previous section, nestinghabitat occurs throughout the province. Nestrecords mapped by Campbell et al. (l990)indicate the coast provides more or betterhabitat than the Interior, and that the southernInterior is better than the north.
The distribution and importance of nestinghabitat is described in tables 4 and 5 for eachmajor biogeoclimatic zone within each of
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nine ecoprovinces (Figure 3) occurring inBritish Columbia. The Coastal WesternHemlock (CWH) Zone in the Coast andMountains Ecoprovince contains by far themost extensive and important nesting habitat.The Coastal Douglas-Fir (CDF) and CWHzones of the Georgia Depression are alsoimportant, but less extensive. In the Interior,much of the best nesting habitat is in theInterior Douglas-Fir (IDF) and Sub-borealSpruce (SBS) zones of the Southern Interior,Central Interior, and Sub-boreal Interior
ecoprovinces, which comprise part of theInterior Plateau. Locally good habitats occuralong valley bottoms in the Southern InteriorMountains Ecoprovince, primarily in the IDFand Interior Cedar-Hemlock (ICH)biogeoclimatic zones. Minor habitats occurin the Boreal White and Black Spruce(BWBS) zone in three northern ecoprovinces(Northern Boreal Mountains; Boreal Plains;Taiga Plains); for example, along the PeaceRiver.
Figure 3. Major Ecoregion subdivisions of British Columbia. Ecoprovinces discussed in thisreport are underlined. (From Demarchi 1988).
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Table 4. Distribution and importance of Bald Eagle nesting and winter habitat in BritishColumbia.
Ecoprovince1 and Season 2 Habitat Features3
Biogeoclimatic of Use and Importance Zone
Georgia DepressionMarine N Extremely important, especially intertidal and shallow
inshore waters, since these supply almost all eagle foodduring the nesting season.
W As for nesting. Large numbers of eagles from outside thisecoregion also feed in marine/estuarine environments inwinter/spring.
CDF N Old-growth stands and veteran trees in second growth orsettled areas are very important for nesting along or near theshoreline of southeast Vancouver Island and the Gulf Islands.Nest trees are predominantly Douglas-fir.
W Shoreline trees are important perches for prey-spotting andnight-roosting. Salmon-spawning streams in this zone alsoprovide important fall and winter food for many eagles fromoutside the ecoregion.
CWH N Provides important nest trees in Campbell River, SunshineCoast and Fraser Valley areas. Nesting trees mostly Douglas-fir and cottonwood.
W As for CDF.
Coast and MountainsMarine N As for Georgia Depression. Many seabird islands in this area.
W As for Georgia Depression. Many seabird islands in this area.CWH N Provides important nest trees along most of the coast. These
probably support over 75% of Bald Eagles nesting in theprovince. Sitka spruce is the most used tree species, butwestern redcedar, western hemlock, Douglas-fir, andcottonwood are also used.
W Shoreline trees are important perches for prey-spotting andnight roosting. Many salmon-spawning streams provide fall-winter food; eulachon runs occur in some rivers in earlyspring.
ICH N Nesting habitat for small numbers of eagles along rivers andaround lakes in the Nass Basin-Upper Skeena area.
W A very small number of eagles may winter in ice-free loca-tions along major rivers.
Southern Interior (Steppe)BG/PP N Ponderosa pine and Douglas-fir trees provide nest sites for a
small nesting population around large lakes in valley bot-toms.
W The most important Southern Interior winter habitat is at ice-free lakes in these zones.
IDF N Provides nest trees for a few pairs that nest around smallerlakes or along meandering rivers/streams.
W A very limited amount of winter habitat occurs along largerrivers or at lake outlets in the lower elevations of this zone.
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Table 4. (Continued)
Ecoprovince1 and Season 2 Habitat Features3
Biogeoclimatic of Use and Importance Zone
Southern Interior (Steppe) (continued)MS N Small areas of nesting habitat probably occur around lakes in the
lower part of this zone (e.g., Pennask, Tunkwa, or Loon Lakes).W No wintering expected.
Southern Interior MountainsPP/IDF N Some of the best nesting habitat in this ecoregion occurs in these
zones, i.e., along major rivers and around lakes and wetlands onthe floor of the Rocky Mountain Trench from the U.S. border toDonald. The main nest trees are cottonwoods on riverfloodplains.
W Winter habitat includes ice-free areas at lake outlets (e.g.,Columbia, Windermere) and other valley bottom areas wheretraffic-killed ungulates are available. However, few eagles winterhere.
ICH N Best nesting habitat are at wetland complexes, such as CrestonValley, where a variety of food is available. Nest trees there aremostly cottonwood. Nesting habitat used by scattered pairsoccurs around major lakes/reservoirs like Kootenay, Arrow,Shushwap, and Quesnel.
W Small areas of winter habitat occur where rivers do not freeze(e.g., Columbia between Castlegar and U.S. border).
MS N The occasional pair may nest at lakes in this zone.W No winter use expected.
Central InteriorIDF N Many lakes and wetland complexes on the southern part of the
Interior Plateau Ecoprovince provide fair to good feeding habitatduring the nesting period. Douglas-fir is the main nest tree.
W Very little winter habitat in this zone. The occasional eaglewinters along major valleys and subsists largely on carrion.
SBS N Forest stands at large lakes in the Tweedsmuir-Burns Lakeregion support some nesting eagles, as do those along rivers likethe Morice. Cottonwoods are frequent nest trees, but aspen,Douglas-fir, and spruce are also used.
W Small areas of winter habitat occur at outlets of large lakes (e.g.,Morice) or below dams (Skins Lake). However, very few eagleswinter in this zone.
SBPS N This zone has few large lakes; however, a few eagles nest alonglake/river systems like the Blackwater (West Road).
W No winter use expected.
Sub-Boreal InteriorSBS N Nesting habitat occurs around large lakes, such as Babine,
Stuart, and Takla; at smaller lakes in the Vanderhoof andQuesnel areas, and along rivers like the Nechako and Fraser. Avariety of species of trees is used for nesting, but cottonwoodsand aspens appear to predominate along rivers.
W Very little winter habitat is present. The occasional eaglewinters along major rivers and at garbage dumps.
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Table 4. (Continued)
Ecoprovince1 and Season2 Habitat Features3
Biogeoclimatic of Use and Importance Zone
Northern Boreal MountainsBWBS N Virtually all nesting in this ecoregion is expected to be in the
BWBS Zone. Most nests are associated with large lakes, suchas Atlin, Teslin, or Kinaskan. Nesting records are very sparsein this area.
W No significant winter habitat is present.
Boreal PlainsBWBS N Cottonwood stands along the Peace River between Hudson
Hope and the Alberta border support a few nesting pairs.Occasional pairs nest elsewhere around lakes/wetlands.
W Occasional birds winter along the Peace, which does notfreeze for some distance below the Bennett Dam.
Taiga PlainsBWBS N Scattered nesting probably occurs at large lakes like Kotcho.
Trees used for nesting, and important food sources in thisarea are not known.
W No winter use is expected.
1 Biogeoclimatic zones of marginal occurrence in any ecoprovince and those in which little or no nesting or winteruse are expected to occur are omitted. Ecoregion names follow Demarchi (1988); biogeoclimatic zones are fromMinistry of Forests (1988).
2 N = Nesting season useW = Winter (Fall/Winter/early Spring) use.
3 Habitat importance is subjectively rated in Table 5.
3. Characteristics of nest trees
Campbell et al. (l990) list ll species of treesused for nesting in British Columbia and notethat, on the coast, Sitka spruce is used mostfrequently (70%), followed by Douglas-fir(l8%), other conifers (western redcedar, west-ern hemlock, and lodgepole pine combined =7%), cottonwood (5%), red alder (<l%), andwillow (<l%). In the Interior, those authorsfound cottonwood to be most often used(52%), followed by aspen (21%), Douglas-fir(21%), ponderosa pine (5%), and spruces(l%). R. Davies (pers. comm.) states thatwestern hemlock is used as frequently as, ormore than, any other tree species along thesouthwest coast of Vancouver Island. Two ad-ditional species used occasionally on thecoast are grand fir and bigleaf maple (D.Blood, pers. comm.).
Local and regional variation in tree speciesselection is indicated in Table 6. On thecoast, Douglas-firs predominate in the Gulfof Georgia area and Sitka spruce on the northcoast, while western redcedar may be themost used tree in some outer coast locationswhere old-growth stands still occur. All threeof these species are highly valued by the for-est industry. Coastal nesting in cottonwoodsis primarily along river floodplains and del-tas. In the Interior, most eagles nesting alongrivers use cottonwoods; those on uplandsaround lakes, at least in the South and Cen-tral Interior, largely use Douglas-firs or as-pen. Ponderosa pines are locally importantalong valley bottoms in the Thompson-Okanagan region.
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Table 5. Estimated relative importance of ecoprovinces, and biogeoclimatic zones withinthem, for providing Bald Eagle nesting and wintering habitat.
Ecodivision/Ecoprovince1 Habitat2 Habitat importance3
Nesting season Winter
HUMID MARITIME AND HIGHLANDSGeorgia Depression Marine H H
CDF H HCWH H HMH N N
Coast and Mountains Marine H HCWH H HICH L L/NMH N NAT N N
SEMI-ARID STEPPE HIGHLANDSSouthern Interior PP/BG L L
IDF M LMS L N
ESSF N NAT N N
HUMID CONTINENTAL HIGHLANDSSouthern Interior Mountains IDF/PP M L
ICH M LMS L/N N
ESSF N NAT N N
Central Interior BG L/N L/NIDF M L/NSBS M L
SBPS M NMS L/N N
ESSF N NAT N N
Sub-boreal Interior SBS M LESSF N N
AT N N
SUB-ARCTICTaiga Plains BWBS L/N N
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Table 5. (Continued)
Ecodivision/Ecoprovince1 Habitat2 Habitat importance3
Nesting season Winter
SUB-ARCTIC HIGHLANDSNorthern Boreal Mountains BWBS L L/N
SWB L/N NAT N N
BOREALBoreal Plains BWBS L L
1 Demarchi 1988.2 Biogeoclimatic zones based on Ministry of Forests 1988. Marine habitat type added in coastal ecoprovinces.
CDF = Coastal Douglas-FirCWH = Coastal Western HemlockMH = Mountain HemlockBG = BunchgrassPP = Ponderosa PineIDF = Interior Douglas-FirMS = Montane SpruceESSF = Englemann Spruce-Subalpine FirICH = Interior Cedar-HemlockSBPS = Sub-boreal Pine SpruceBWBS = Boreal White and Black SpruceSWB = Spruce-Willow-BirchAT = Alpine Tundra
Biogeoclimatic zones only marginally represented in an ecoprovince are not included (e.g., IDF in Coast and MountainsEcoprovince).
3 H = High importanceM = Moderate importanceL = Low importanceN = No importance
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Table 6. Regional variation in tree species used for nesting by Bald Eagles in British Columbia.
Location and source Number Tree speciesof nests
Fraser Delta and Valley(Butler and Campbell l987) 3 All cottonwood(Dunbar l988) 14 8 cottonwood; 4 Douglas-fir; l spruce;
l bigleaf maple
Gulf Islands(Vermeer et al. l989) 35 All Douglas-fir
Nanaimo area(Blood l989a) 65 61 Douglas-fir; 3 grand fir; l cottonwood
Barkley Sound(Vermeer and Morgan l989) 25 l5 w. redcedar; 5 w. hemlock; 4 Sitka spruce;
l Douglas-fir
Quatsino Sound(Lueke-Joyce l989) 61 32 Sitka spruce; l5 w. redcedar; 9 Douglas-
fir; 5 w. hemlock
Queen Charlotte Islands(Rodway et al. l988) 85 74 Sitka spruce; 2 w. redcedar; l red alder;
8 snags
Okanagan(Cannings et al. l987) 5 4 ponderosa pine; l cottonwood
East Kootenay(Forbes and Kaiser l984) 26 25 cottonwood; l Douglas-fir
Cariboo(Blood and Anweiler l990) l8 l5 Douglas-fir; 3 cottonwood
Cheslatta Lk.-Nechako R.(Blood l983) 30 21 cottonwood; 8 aspen; l Douglas-fir
Peace River area(Siddle l990) 6 All cottonwood
In British Columbia, as elsewhere, tree size,form, and location are more important thantree species. Nest trees are usually dominantor co-dominant specimens (in size) in thestand in which they occur, have developedsturdy branches and a fairly open branchstructure, and are located at or near shore-lines. On the coast, gnarled old-growth coni-fers, often approaching decadence, areselected if available, although few actual ages
of nest trees have ever been determined. ADouglas-fir nest tree felled near Duncan wasabout l90 years old (D. Blood, pers. comm.).Conifers as small as 0.6 m DBH have beenused on the coast (Table 7); however, smalldiameter trees may still be locally the largest,and may be old trees on poor growing sites.Lueke-Joyce (l990) reported two nests in sec-ond-growth trees on northern Vancouver Is-land; however, actual size and age of those
27
trees is not stated. Cottonwood and aspennest trees are probably younger on averagethan are coniferous nest trees, although datato confirm this are lacking. Information isneeded on the time needed for various treespecies in various regions to reach a size andform suitable for Bald Eagle nesting.
Nests are often in partly dead trees and occa-sionally in completely dead ones. None of65 trees used for nests in the Nanaimo areawas completely dead at the time they were
used by eagles (Blood l989a). At BarkleySound, Vermeer and Morgan (l989) reportedthat three of 25 nest trees were dead. Datafrom three Interior areas (Blood l982; Bloodand Anweiler l983, l990b) indicate ll of 61nest trees (l8%), most of which were cot-tonwoods, to be dead. Some dead trees mayhave been living when nesting in them wasinitiated. Bald Eagles sometimes use nestsbuilt by ospreys (Campbell et al. l990) andthese are frequently in dead trees.
Table 7. Some characteristics of Bald Eagle nest trees in British Columbia.
Parameter1 Location2
Nanaimo Gulf Islands Barkley Sound Queen Charlotte Nechako R.(65) (35) (25) Isl. (73) (21)
Tree diameter (DBH)
Mean 1.3 l.l 2.3Range 0.6-2.1S.D. 0.3 0.8
Tree heightMean 36.l 38.6 35.6Range l6.9-58.5S.D. l0.8 13.8
Nest heightMean 30.3 32.4 30.3Range 12.5-48.8S.D. 4.5 13.3
Distance from shoreline3
Mean l73 62 42 24 77Range 4-850 0-300 3-250S.D. 45 24
1 all measurements in meters2 Sample sizes in parentheses
Nanaimo data from Blood 1989aGulf Islands data from Vermeer et al. 1989Barkley Sound data from Vermeer and Morgan 1989Queen Charlotte data from Rodway et al. 1988Nechako River data from Blood and Anweiler 1983.
3 distance from high tide in coastal areas and from nearest river channel along the Nechako.
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4. The nest tree environment
Nest trees are almost always near aquatichabitats of one kind or another, and usuallysituated so that at least part of the aquatic for-aging habitat is visible from the nest. Themean distance of nests from adjacent shore-lines in various parts of British Columbiaranged from 24 to l73 m (Table 7). Thenumber of nests normally decreases with in-creasing distance from shorelines. Althoughnot indicated in Table 7, some nests areknown to occur l km or further inland. Theseare usually missed during aerial surveys thatfollow shorelines. Inland nesting appears tobe most common where the nearshore area isheavily settled or logged and hence supportsfew or no suitable nest trees, for example, thesoutheast coast of Vancouver Island.
Nests occur in extensive, dense old-growthstands, fragmented old-growth parcels, and inlone veteran trees standing in second-growthforest or logging slash. The age and speciescomposition of the surrounding forest appearto have little influence on nesting occurrence.Although some lone trees left standing inlarge logging slashes continue to be used(Farr l988), the generality of this behaviour isnot known and the long-term acceptability ofsuch trees requires further study.
The environment of Bald Eagles nesting inBritish Columbia varies from pristine wilder-ness to urban landscapes. Nesting eagles areremarkably tolerant of human activity in theirvicinity as long as their nest, nest tree, andforage resources are not disturbed. Blood(l989b) reported that several nests occurwithin the city limits of Nanaimo, some vir-tually surrounded by residential or industrialdevelopment. In Greater Vancouver, nestshave been reported at Lighthouse Park and 4km west of Park Royal (A. Rahme, pers.
comm.), in Stanley Park (Campbell et al.l974), at Alaksen National Wildlife Area andalong the South Arm of the Fraser River(Butler and Campbell l987), and in the BeachGrove and Tsawwassen area (A. Poynter,pers. comm.). There are undoubtedly otherexamples of nesting in urban and suburbanenvironments in the province. Juvenile eaglesfledged in such environments are expected toaccept similar situations for nesting whenthey reach breeding age. Heavily developedareas however, appear to support fewer nest-ing pairs than would be expected under pris-tine conditions. This is largely due to loss ofnest trees and foraging habitat, rather than asimple aversion to the presence of people andcultural landscapes.
The nesting environment always includesa foraging area of sufficient productivity tosupport the nesting pair and their younguntil fledging. On the coast, this invariablyincludes the adjacent intertidal zone andnearshore waters. Inland, foraging habitatat nest sites includes river channels, shore-lines and surface waters of lakes, andwetlands of various kinds. Information onforage resources is given in Section 6.5.1Food Resources (Also see Table of Contents)
2.1.3 Food Resources
Winter habitat
l. Food supply
Ice-free aquatic environments are the majorcomponent of Bald Eagle winter habitat inBritish Columbia. This includes marinehabitats along the entire coast, most low-elevation rivers, lakes and wetlands west ofthe Coast Range, and large lakes and rivers inthe Southern Interior. Within their BritishColumbia winter range, the abundance ofeagles varies greatly from place to place and
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month to month in response to availability offood. There is a greater tendency for largenumbers of eagles to concentrate in localareas during winter than during the nestingseason.
Salmon-spawning streams are the most im-portant coastal habitats in winter especiallythose with large runs of chum, pink, or cohosalmon (Dickie l990). Spent carcasses areavailable from October to January or later.Tree stands along these streams provideperches for food-spotting and cover fornight-roosting. Other fish concentrations,such as staging and spawning herring in ma-rine waters and eulachon runs into coastalrivers, attract many eagles in spring. Estuar-ies and tidal mudflats that support winteringwaterfowl are also important, especially onthe south coast (Butler and Campbell l987).Although the above habitats are of greatestimportance, eagles use the entire coastline inwinter. In the Interior, large lakes in theSouthern Interior that support wintering cootsand ducks are of some importance (Canningset al. l987), but the number of eagles presentis small when compared to coastal habitats.Valley bottoms where ungulate carrion isavailable, and ice-free rivers below powerinstallations, also provide winter habitat for afew Interior birds.
2. Perching and roosting habitat
Daytime perches and night roosts are impor-tant components of winter habitat in BritishColumbia. Diurnal perches, used for surveil-lance of potential prey, are primarily snagsand deciduous trees along salmon-spawningstreams (Farr l988), or snags and decadent orspindly conifers along marine shorelines. Ea-gles here also perch on pilings and logbooms, and on the ground on mudflats, riverbars, or offshore reefs.
The use of communal night roosts has beenevaluated in the Fraser Valley by Farr (l988)and Teske (l989). Eighteen night roosts havebeen identified in the eastern Fraser Valley,seven in valley bottom cottonwood standsand ll in hillside conifer stands. Roost treeswere usually the tallest and largest Douglas-firs and cottonwoods at each site. Distancesof roosts from major feeding areas variedfrom 0 to 5 km. Cottonwood roosts aremostly along river channels and are used forboth diurnal perching and night roosting.Communal roosts undoubtedly occurthroughout the winter range of Bald Eaglesin the province, but have yet to be identified.
3. Habitat distribution
The distribution and relative importance ofwinter habitat in British Columbia is summa-rized by ecoprovince and biogeoclimaticzone in Tables 4 and 5. Based on data in Farrand Dunbar (l988), it is likely that habitatswest of the Coast Range support over 95% ofthe British Columbia eagle population inmid-winter. This probably does not apply inautumn, when spawning salmon and kokaneeruns are available in the Interior and watersthere are still ice-free.
The CWH Zone of the Coast and MountainsEcoprovince, including adjacent marine wa-ters, provides the bulk of Bald Eagle winterhabitat; although habitats in the GeorgiaDepression probably support more eaglesper unit area than the north and outer coast.Most Interior wintering habitat is in theBunchgrass, Ponderosa Pine, Interior Doug-las-fir, and Interior Cedar-Hemlock zones ofthe Southern Interior, Central Interior, andSouthern Interior Mountains ecoprovinces(Table 5).
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Migration habitat — On the coast, habi-tats used by spring migrants are similar tothose used in winter, except that salmon-spawning streams are no longer important.Herring-spawning sites, eulachon-spawningrivers, and estuaries/mudflats used by mi-grant waterfowl are of key importance, butmarine habitats along the entire coast areused. In the Interior, wintering habitats arealso important for spring migrants; however,they also use a variety of other sites, suchas small ice-free areas at lake inlets oroutlets, game winter ranges where carrion isavailable, or flooded farmlands that attractwaterfowl. Spring habitat in the Interior islargely restricted to low elevation valleysand plateaus.
In fall, important habitats for coastal mig-rants include salmon-spawning streams,estuarine waterfowl habitat, and the marineenvironment generally. In the Interior, BaldEagles occur very widely in fall and may beseen at kokanee- and sockeye-spawningstreams, waterfowl and muskrat marshes, oranywhere that carrion is available.
Food resources — Food habit informa-tion tells a great deal about the ecology ofa species - why certain habitats are selectedfor nesting and why certain seasonalaggregations occur - and assists in definingcritical habitats. These are matters of impor-tance for assessing the present and futurestatus of Bald Eagles in the province, there-fore, some attention to food habits withinBritish Columbia is in order.
General information on Bald Eagle foodhabits in British Columbia is given by Brooks(l922), Munro (l938), Beebe (l974), andCampbell et al. (l990). The versatility of thisspecies was noted by Munro (op. cit.), whostressed
“... how local conditions and time of yearmodify the food habits of the Bald Eagle.”
Information for British Columbia (Tables 8and 9) confirms the wide range of food itemsnoted by investigators in other areas. How-ever, the seasonal and regional importance ofvarious food items is more difficult to assess.Semi-quantitative studies here are confined tothe coast, involve primarily the nesting sea-son, and are based on food remains picked upunder nests (Vermeer et al. l989; Vermeerand Morgan l989). For various reasons, thesemay not accurately reflect the weight of vari-ous food items ingested by eagles. Otherfood habit information largely involves listsof species that eagles have been seen to catchor scavenge upon. Though not quantitative,these provide a fair appreciation of seasonallyand locally important food sources.
On the coast, frequently observed concentra-tions of eagles at sites of spawning salmon(late August through January), eulachon runs(March-April), pre-spawning and spawningschools of herring (January-April), and hakeat tidal rapids (May-June) suggest that fish,obtained live or as carrion, is the most impor-tant dietary item on a year-round basis.Where locally abundant, birds may predomi-nate in the diet, for example, at and nearseabird colonies during the nesting seasonand in the Fraser Delta-Boundary Bay areain winter. Intertidal invertebrates are ofwidespread importance on the coast andmay be of high importance on the outer coastin summer.
In the Interior, fish are also importanteagle foods. This includes spring spawningconcentrations (rainbow trout, suckers,squawfish) available in the nesting season,fall spawners (salmon, kokanee, char) takenby a more mobile post-breeding eagle
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population, as well as surface-dwelling fishat any season. The association of eaglenests with many lakes and rivers that sup-port few waterfowl in late spring and earlysummer, and heavy reliance of other inlandeagles on fish in the nesting season(Gerrard and Bortolotti l988), suggest thatfish are the most important dietary item forinterior British Columbia eagles duringnesting. In restricted areas with significantwaterfowl production (e.g., Creston Val-ley), waterfowl may assume some impor-
tance for nesting eagles. Waterfowl seem tobe most commonly taken during spring mi-gration, in fall migration/staging areaswhere sport hunting provides ducks thatare crippled or unretrieved, and in winteron the southern interior lakes that do notfreeze. In the latter situation, coots and div-ing ducks may form the bulk of the diet.Ungulate carrion resulting from traffic orpredator kills, and viscera left by huntersare also important in the southern Interiorfrom autumn to early spring.
Table 8. Food habits observations for Bald Eagles in coastal British Columbia.
Location and Source Food Habit Observations
Lower Mainland
Butler and Campbell l987: Bald Eagles at the Reifel Sanctuary have been observed feeding on Red-necked Grebe, Great Blue Heron (frozen carcass), Trumpeter Swan carcass,Canada Goose, Snow Goose (crippled), Green-winged Teal, Mallard, Ameri-can Wigeon, Greater Scaup, Surf Scoter, Short-eared Owl, Ring-neckedPheasant, American Coot, Mew Gull and California Gull. Mammals identifiedincluded Muskrat and River Otter caught in traps, and dead domestic stock.
A. Poynter, pers. comm. l990: In winter l989/90, observed eagle kills at Boundary Bay involved NorthernPintail (12+), Green-winged Teal (several), Bufflehead (several), GreaterScaup (2 or 3), Glaucous-winged Gull (3), Mallard (2), American Wigeon (l),Ruddy Duck (l), Thayer’s Gull (l), Western Grebe (l), Common Loon (l), andRed-breasted Merganser (l). Two of the ducks were taken from Northern Har-riers. Many of the birds taken were crippled or injured, presumably by hunt-ers.
Fry l980: Bald Eagles were seen from January onward, sitting on tidal flats with duckkills. An eagle was observed eating what appeared to be a Dunlin.
Campbell et al. l972: Reported an eagle carrying a Muskrat at Reifel Island.Farr and Dunbar l988: Report a strong association of eagles with salmon-spawning streams (e.g.,
Squamish R., Harrison, R.) in January.
Southeast Vancouver Island and Gulf Islands
Vermeer et al. l989: Frequency of prey remains beneath nests was 52% birds (mostly Glaucous-winged Gulls), 34% fish (mostly Ling Cod and rockfish), 12% marine inverte-brates (mostly crabs and clams), and 2% mammals (mostly carrion).Glaucous-winged Gulls were by far the most frequent species of prey. Up to50 eagles attracted to hake brought to surface by upwelling in Active Pass.
Trenholme and Campbell l975: Noted eagle concentrations in February associated with lambing of domesticsheep, and reported that eagles had been seen feeding on still-born lambs andafterbirth.
Hancock l964: Dead sheep reported to be a major winter food on several Gulf Islands; how-ever, fish were felt to be the most common food. Predation on Glaucous-winged Gulls and on a crippled American Wigeon also noted.
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Table 8. (Continued).
Location and Source Food Habit Observations
Southeast Vancouver Island and Gulf Islands (cont.)
Tatum l972: Reported 21 eagles feeding on a deer carcass near Duncan in winter.Cassidy l985: Described up to 270 eagles attracted to spawning salmon at the Qualicum
River in late fall and early winter.
West Coast Vancouver Island
Vermeer and Morgan l989: Frequency of prey items under nests in Barkley Sound was 45% marine inver-tebrates (mostly littleneck clam and mussels), 41% birds (Glaucous-wingedGull most frequent species), l0% fish, and 4% mammal.
Hatler et al. l978: Evidence is given for feeding on octopus, crabs, skate, herring, salmon,seaperch, Kelp Greenling, Red Snapper, Cabezon, Midshipman, Pacific Loon,Pelagic Cormorant, Canada Goose, ducks, gulls, River Otter, Northern FurSeal, Northern Sea Lion, and Mink. Some of the fish had been discarded byfishermen or taken from otters, and many of the waterfowl were thought tohave been disabled by hunters. Marine mammals were obtained as carrion.
Carl et al. l950: On several occasions, eagles were flushed from the remains of sea lion pups atTriangle Island, a sea lion breeding site.
Vermeer et al. l990: One eagle nest at Triangle Island, examined after the breeding season, con-tained the remains of one young Common Murre, at least l0 Cassin’s Auklets,one Tufted Puffin, and two large unidentified alcids.
Rodway et al. l990: At the Triangle Island seabird nesting colony, observed prey of eagles includedGlaucous-winged Gull chicks, Common Murres, Cassin’s Auklets, RhinocerosAuklets, Tufted Puffins, and rabbits. Scavenged sea lion pups were regularlyencountered.
Queen Charlotte Islands
Vermeer et al. l984: Ancient Murrelets were the main eagle prey in a mixed nesting colony of thatspecies and Cassin’s Auklet. Murrelets were killed by eagles when they arrivedat their nesting burrows at night.
Rodway et al. l988: Document considerable predation by Bald Eagles on Ancient Murrelets,Cassin’s Auklets, storm-petrels and many other seabirds at seabird nesting is-lands along the east coast of Moresby Island. Most eagle nests in this areawere in or near seabird colonies.
Reimchen and Douglas l977: 60% of eagle feeding observations involved active predation on fish and birds.Attempted or successful predation was recorded for Common Loon, Red-throated Loon, Mallard, Northern Pintail, Green-winged Teal, CommonGoldeneye, Bufflehead, Oldsquaw, and Cassin’s Auklet. Carrion sources in-cluded spawned salmon, Lingcod, pinnipeds, cetaceans, and deer.
Douglas and Reimchen l988: 24% of pre-fledged Red-throated Loon chicks were taken by Bald Eagles.Munro l938: “... in the spring... most of their food (at Tlell) is taken from the sea beach and
from the boulder reefs exposed at low tide.” Many dogfish and one deer eatenas carrion along the beach. Food items under a perch included crabs (the mostfrequent item), dogfish heads and tails, feathers of a pintail, sternum of a duck,and bones of a rabbit. Includes accounts of predation on juvenile CommonMergansers.
Brooks l922: Reported having seen eagles take Holboell’s (Red-necked), Horned, and West-ern Grebe, Red-throated and Common Loon, Glaucous-winged Gull, Ameri-can Coot, mergansers, Mallard, Northern Pintail, American Wigeon, Scaup,Bufflehead, and scoters near Masset.
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Being intelligent scavengers and also quitetolerant of non-threatening human activity,eagles have taken advantage of many foodsources made available by humans. Theseprobably allow some areas at some seasonsto support more eagles than would otherwisebe the case. They may also present problems,such as ingestion of lead shot and the pickingup of toxic substances through feeding onwaste matter. Some human influences oneagle food habits that have been observed inBritish Columbia are described below.
1. Fish and Wildlife Harvest
Discarded fish: Unwanted fish and heads/en-trails of desirable ones discarded by commer-cial and sport fishermen are of considerableimportance for coastal eagles from spring tofall. Beebe (l974) described eagles flying 5km to sea to pick up discarded rockfish orratfish drifting behind a salmon troller. Hatleret al. (l978) report a sighting of 63 eaglesfeeding around a shrimp boat in BarkleySound. Blood (l989b) noted that eagles fre-quently perched near boat ramps, waiting forincoming fishermen to eviscerate their catch.Vermeer et al. (l989) felt that many benthicfish remains beneath Gulf Island nest sitesprobably originated from fishermen becausethey consisted only of heads and parts of the
pectoral girdle. Barrett (pers. comm. l990) re-ports that sport fishermen in the Stuart Islandarea regularly feed non-releasable rockfish towaiting eagles, some of which have learnedto respond to a whistle. Ten lodges and l00guides operate in that area.
Parts of harvested game and fur animals:Entrails from hunter-killed ungulates arewidely available in fall. Carcasses of trappedfurbearers may be a minor food source, butare fed on by some migrant eagles in spring.Ravens and other scavengers compete witheagles for these foods.
Traffic-killed ungulates: Hundred of biggame animals are killed by road and railtraffic each year in British Columbia, andmany of these are scavenged by Bald Eagles.This appears to be a fairly important foodsource for Southern Interior eagles in winterand spring (Hatler l983; Kinley, pers. comm.l990).
Wounded waterfowl: Waterfowl crippled byhunters or shot and not retrieved are locallyimportant in fall and winter at locations suchas Boundary Bay (Poynter, pers. comm.l990), Tofino (Hatler et al. l978), and Fort St.John (Siddle l990).
Table 8. (Continued).
Location and Source Food Habit Observations
Northern Coast
Ofelt l976: Describes eagles feeding on salmon chased to the surface by killer whalesin Johnstone Strait in summer.
J. Barrett pers. comm. l990: Reports up to ll0 eagles at Jimmy Judd Island in May and June, feeding onhake in tidal rapids of Gillard Passage, near Stuart Island.
R. Pojar, pers. comm. l990: Noted 320 eagles associated with a eulachon run in the lower Skeena Riverin March l989.
Kaiser l989: Reports eagle depredation on adult Rhinoceros Auklets and on Glaucous-winged Gull eggs at a seabird nesting colony near Prince Rupert.
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Table 9. Food habits observations and inferences for Bald Eagles in the Interior of BritishColumbia.
Location and Source Food Habit Observations
Okanagan
Cannings et al. l987: Noted association between eagles and waterfowl concentrations in lateMarch; American Coot felt to be a favoured winter prey; describes attackon a Western Grebe.
Brooks l922: “On Okanagan Lake... the Bald Eagle preys very largely on coots duringthe winter when these birds are out in the open water in large flocks.”
Kootenay
Forbes and Kaiser l984: 13 prey items under two nests included 4 American Coots, 3 pintails, l div-ing duck, 2 Muskrats, 3 squawfish and l Black Bullhead. Foraging eagleswere seen capturing an American Coot and a Muskrat and scavenging 2Black Bullheads and a Largescale Sucker.
Kinley, pers. comm. l990: Commonly saw one to six eagles on road-killed elk or deer in winter in theRocky Mountain Trench. Larger numbers apparently associated withKokanee spawners in fall.
Interior Plateau
Munro l938: Reported many eagles attracted to spawning runs of Kamloops trout andsuckers in spring, near Vanderhoof.
Munro l938: Found remains of l Goldeneye Duck, l Ruffed Grouse, one or more suck-ers, and two or more Kamloops trout under a nest at Horse Lake. Alsonoted importance of American Coots in winter on large lakes of southernB.C. that do not freeze.
Peace River
Siddle l990: Reported that migrant eagles are attracted to large flocks of early arrivingducks in spring - Mallard, Northern Pintail, and American Wigeon. De-scribes an attack on a pintail. Other reported foods were discarded Beavercarcasses, remains of a hunter-killed Moose, spawning suckers at CharlieLake, fish that have passed through turbines at dams near Hudson Hope,and ducks wounded by hunters.
Northern Interior
Beebe l974: “... the most frequently captured mammals are hares. Where Bald Eagleslive and reproduce inland, such as in the boreal forest, some pairs becomehighly oriented to this kind of prey...”.
Various locations
Farr and Dunbar l988: During the l988 mid-winter count, deer carcasses were reported as fooditems at Castlegar, Grand Forks, and Smithers.
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2. Agricultural Activity
Winter-killed sheep, stillborn lambs, andafterbirth attract eagles in the Gulf Islandsand a few other areas. Farm and ranch offal isavailable in a variety of rural areas. Campbellet al. (l990) noted an attraction to livestockcalving grounds in the Interior in spring.
3. Habitat Alteration
Enhancement projects: Wetland develop-ments, such as Reifel Refuge, SerpentineFen, Creston Valley, and numerous DucksUnlimited projects have increased popu-lations of breeding and/or wintering water-fowl, plus those of Muskrats and fish insome locations. Forbes and Kaiser (l984)noted that extensive impoundment ofmarshes at Creston resulted in large increasesin breeding waterfowl, Coots, Muskrats, andcoarse fish, and that this was probablyresponsible for an increase in the nestingeagle population. Salmonid enhancementprojects, such as spawning channels andpassage facilities have increased the availabil-ity of eagle food in some areas.
Hydroelectric projects: Fish that are killedor stunned when passing over spillways orthrough turbines, and others that congregatebelow dams because upstream movement isimpeded, are food for a few eagles that havelearned to capitalize on this source. Becauserivers are ice free for some distance belowthese dams, eagles are able to find food andover-winter in Interior areas where they wereformerly rare.
Waste disposal sites: Farr and Dunbar (l988)reported that about 2% of Bald Eagles seenduring the l988 mid-winter count were at ornear garbage dumps. Dumps are also feedingsites in summer, although the proportion of
the population using them is probablysmaller than in winter. Sewage lagoons andoutfalls attract many ducks, gulls and otherbirds, which in turn attract eagles. Use ofthese sites is primarily by migrants in the In-terior and wintering birds on the coast.
4. Faunal Introductions
Introductions, such as deer into the QueenCharlotte Islands and cottontail rabbits toVancouver Island, provide carrion and preythat were previously not available. Introduc-tion of sport fish to various Interior lakes andreservoirs, and of invertebrates like the Japa-nese oyster and Japanese little-neck clam onthe Coast have also provided new foodsources (Carl and Guiguet l958).
2.2 Habitat Impacts and Trends
A variety of human-caused impacts haveaffected Bald Eagle habitat in BritishColumbia, or could do so in the future. Thesemay be summarized as follows:
2.2.1 Removal of nest trees
This is mostly attributable to logging; how-ever clearing for settlement (residential, in-dustrial, commercial), agriculture, and otherpurposes also contributes to the impact. Lin-ear developments, such as highways, trans-mission lines, and pipelines, frequentlyfollow valley bottoms or parallel rivers, fur-ther reducing the stock of potential nesttrees. Hydro dams have flooded habitat insome areas.
Logging — Logging is of greatest con-cern because it is so widespread; because themost valuable forestry lands are at low eleva-tion in Interior valleys and along the coastwhere most eagle nesting also occurs; and
36
because standard forest rotations are too shortto allow preferred species of nest trees to de-velop the old-growth size and form neededfor nesting (Morgan et al. l985). Although lit-tle information is available on the actual ageof nest trees, there is little doubt that mostconifers used in the Pacific Northwest couldbe called “old growth” based on their large di-ameter and height (Blood l989a; Vermeer andMorgan l989; Vermeer et al. l989). Hodgesand Robards (l982) estimated the mean age ofnest trees in southeast Alaska to be 400 years.Aspen and cottonwood, important nest treesin Interior British Columbia, are relativelyfast growing and may provide nest sites at ayounger age than conifers, but this requiresevaluation. In any event, deciduous trees usedfor eagle nesting are probably old-growthspecimens of the species involved. Second-growth conifers, and probably deciduous treesas well, do not attain a size and form neededfor nesting by Bald Eagles prior to being har-vested. Therefore, much of British Colum-bia’s commercial forest land will never besuitable nesting habitat for Bald Eagles. Theproportion of forest land supporting secondgrowth is steadily increasing. Increasing har-vest of floodplain cottonwoods and upland as-pens is of great concern. Although data onpre- and post-logging nest densities are notavailable, it seems obvious that nestingpopulations must have been reduced in areaswhere extensive clear-cut logging of shorelineand backshore habitats has occurred. Rela-tively normal nesting populations may remainin areas that are extensively logged if remnantold-growth trees or small stands are left andare distributed in a pattern that allows optimalaccess to aquatic food resources during thenesting season. Some areas logged prior tol950 support many scattered veteran treesamong the second growth and may have near-natural nesting populations. The trend towardextensive clear-cutting in recent decades is
not encouraging, even if existing nest trees areidentified and protected.
Settlement — Land clearing for settle-ment, including residential, commercial,institutional, and industrial uses, has beengoing on for decades, and is accelerating. Itis of most concern on the south coast andin Southern Interior valleys, areas that havehistorically provided above-average BaldEagle nesting habitat. Waterfront and waterview properties are in high demand, bothon the seacoast and along Interior lakes andrivers, where increased land clearing can beexpected as long as the human populationof the province continues to grow. There arerecent documented cases of nest trees havingbeen felled during land clearing for residen-tial development on Vancouver Island; in onecase, fledgling eagles were in the nest. Inother situations, voluntary restraint by clear-ing contractors and/or vigilance by nearbyresidents have resulted in lone nest trees be-ing left in subdivided land. Such trees may ormay not continue to be used by eagles andare vulnerable to windthrow and otherenvironmental stresses, and will eventuallydie. If no nearby alternative trees are avail-able, the nesting territory is permanently lost.Fortunately, most nesting habitat on the outerand northern coast is probably safe fromsettlement impacts.
Agriculture — Land clearing for agricul-ture is of some concern in the Fraser Valleyand in Interior valleys. Removal of riparianand floodplain woodlands has been increas-ing in order to maximize farm production. Itis likely that relatively few nest sites havebeen removed to date, and it is hoped thatthese activities will not have a major impactin the future because so much of the BritishColumbia landscape is unsuited for intensiveagriculture.
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of eagles. A variety of tree species are usedfor communal night roosts in the PacificNorthwest; however, most are old-growthstands, and coniferous trees are thermallymore favourable than deciduous species(Anthony et al. l982). Old-growth foreststands along coastal streams having largelate-fall/early-winter salmon runs probablyprovide the most important winter roostinghabitat for Bald Eagles in British Columbia,although little inventory has been done andother kinds of sites may also be important. Itis not known if the removal of such stands todate has had an impact on the fall-wintercarrying capacity or survivorship of BaldEagles. It is presumed that extensive removalof night roosting habitat would be harmful;however, more information is needed onhow much and what kind of roosting habitatis required in various areas.
2.2.3 Contamination of food sources
Although isolated cases of accidental poison-ing are known, there is no evidence thatpollutants such as pesticides, heavy metals,dioxins, or furans have caused direct mortal-ity or reproductive failure in Bald Eagles inBritish Columbia. However, as predatorsand scavengers of animal matter, eagles arevulnerable to trophic magnification of thesesubstances, particularly in aquatic foodchains. The greatest threat is in heavily set-tled and industrialized areas of the province.Increasing industrial development is to beexpected and could worsen the situation.Conversely, increasingly stringent pollutioncontrol regulations may reduce this threat infuture. Monitoring is needed to assess trendsin contamination of key food species.
Other activities — Forest clearing forhighways, transmission lines, pipelines, andother linear developments is of concernwhere these parallel marine, lake, or rivershorelines, which many of them do. Theseare of most concern in valleys where logging,agriculture, or settlement have already re-moved much of the nesting habitat. Even ifexisting nest trees are identified and avoided,linear developments still remove potentialnesting habitat. In more remote areas, indi-vidual linear developments probably do notremove enough nesting habitat to result in adecline in the eagle population. Hydro reser-voirs have flooded river valley nest sites insome Interior valleys. Some eagles nest atthese reservoirs, but it is not known if theirnumbers are lower or higher than prior toreservoir development.
2.2.2 Removal of perching and roost-ing trees
During the nesting season adult eagles usefavourite perches near the nest tree for watch-ing the nest, and elsewhere in their foragingterritory for surveillance of prey or carrion. Inwinter, they also perch by day adjacent tocritical feeding sites, and resort at night toroosts, usually in the shelter of coniferoustrees. As in the case of nest trees, perching/roosting trees and snags may be lost due tologging, settlement, agriculture, or otherkinds of forest removal. Although many his-torically used perches have undoubtedly beenremoved, many remain. As well, require-ments for perching do not appear to be asspecific as for nesting - a wide variety of treespecies and ages, snags, pilings, log booms,etc., are acceptable. Of greater concern is theneed for thermally favourable night roosts inwinter. These are usually adjacent to concen-trated food sources that attract large numbers
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2.2.4 Loss of foraging habitat
Harbour developments like that along theshoreline of Burrard Inlet, together withdredging and filling projects in many inter-tidal areas, have removed some potentialfeeding habitat. However, this is small in aprovincial context. Historically, drainage ofwetlands like Sumas Lake has had local im-pacts, as has the flooding of valley bottomwetlands by reservoirs in more recent years.Development of waterfront land, both alongthe seacoast and Interior lakes and rivers, hasresulted in much human activity along theforeshore and beaches, and this probably in-hibits eagle foraging in such areas. Althoughlocalized, these kinds of impacts are expectedto increase in future years.
2.2.5 Human competition for food
Many forage species important to eagles(e.g., herring, salmon, shellfish, and water-fowl) are also harvested by humans. Exploi-tation to the point of population collapse,locally or regionally, would adversely affecteagles and other vertebrates that share thosefoods. Human impacts on seabird colonies,for example by introduction of predators orby heavy harvest of their marine foods, couldalso have secondary effects on eagles. Im-pacts of this nature have probably occurredon a minor scale in past years, but should beof little significance in the future if the preypopulations are managed for sustained yield.
2.2.6 Regional Impacts in BritishColumbia
Georgia Depression Ecoprovince — Thissmall ecoprovince contains 2 million people,and habitats in it have been more extensivelymodified by humans than those of any otherecoprovince. Despite this, large numbers of
Bald Eagles winter here (Farr and Dunbarl988; Dickie l990) and there is still a substan-tial nesting population (Blood l989; Vermeeret al. l989). Although this suggests consider-able adaptability on the part of the eagles,adaptability has its limits and trends in habi-tat alteration and loss are of great concern.
l. Nesting trees
Historically, logging of old-growth Douglas-fir stands along and near shorelines through-out the ecoprovince must have had aconsiderable impact on nest tree availabil-ity. Morgan et al. (l985) state that prior tologging, late mature and old-growth forestsmade up more than 70% of the CoastalDouglas-Fir Zone in the Georgia Strait area,and that these crucial habitats have declinedto less than 20% and are expected to benearly eliminated within the next century.Present logging is mostly inland, but cuttingwithin 2 km of shorelines is still a threat inrestricted locations on the Sunshine Coast,Vancouver Island between Qualicum andCourtenay, and on several of the GulfIslands. Logging of floodplain cottonwoodsand adjacent uplands in the Fraser Valley isalso a potential threat. However, Farr (l988)reported that eagles continued to nest suc-cessfully in a cottonwood on Herrling Islandin the Fraser Valley after the site was selec-tively logged, and in a nest at NicomenMountain after all surrounding trees wereclearcut. In the Nanaimo area, Blood (l989b)noted accelerating logging of old-growthstands on private land parcels. Where nesttrees are known they are usually left stand-ing; however, logging has greatly reduced theextent of potential nesting habitat and contin-ues to do so.
Land clearing for various settlement uses iscurrently the greatest threat to nesting habitat,
39
and is much more serious here than in anyother ecoprovince. Very little nesting habitatremains in urban areas (Greater Vancouverand Greater Victoria), and significant reduc-tions have occurred along the VancouverIsland shoreline from Campbell River toVictoria, on some of the Gulf Islands, and inthe Fraser Valley. In the Fraser Delta, Butlerand Campbell (l987) stated that “... woodedhabitats have undergone massive alterations.”Despite abundant food resources, they reportonly three nest sites in that area. Clearing forsettlement purposes is proceeding rapidly,especially on Vancouver Island, and the trendis expected to continue for some time. Pre-dominantly private tenure and high realestate values in this area are major obstaclesto preservation of old-growth trees for nest-ing habitat. In the Greater Vancouver area,most known nest trees are in protected areas(Lighthouse Park, Stanley Park, U.B.C.Endowment Lands, Alaksen National Wild-life Area) because few nest trees remain onadjacent lands. In the Nanaimo area, Blood(l989b) found that only ll% of 65 nest treeswere in relatively secure sites, such as dedi-cated parks.
Agricultural land development has histori-cally removed some nesting habitat in theFraser Valley and on Vancouver Island(Comox Valley; Cowichan Valley; SaanichPeninsula). Current agricultural expansion isof minor significance in the ecoregion as awhole, but may still be of concern in someparts of the Fraser Valley.
Linear developments in the Fraser Valleyand on south east Vancouver Island are ofmoderate concern because they tend to paral-lel rivers and coastlines, and because the needfor such developments is expected toincrease in proportion to human populationgrowth. At present, impact assessments usu-
ally identify occupied nest trees, which arethen avoided by the development (Ecclesand Cooper l989). However, considerablepotential nesting habitat is being taken up byrights-of-way of various kinds in thisecoprovince.
2. Perching and roosting trees
Diurnal perch trees at nests and at feedingsites are subject to the same threats and ratesof loss as listed above for nest trees; however,the urgency for conservation action is ratedsomewhat lower than for nesting trees be-cause a variety of sites, such as snags, pilings,and second-growth trees, are acceptable forperching but not for nesting. Farr (l988)noted that eagles continued to use a shorelinestrip of cottonwoods at Waleach Slough inthe Fraser Valley for winter perching after theadjacent inland area was clearcut; however,numbers were lower than in pre-loggingyears. She suggested that leaving patchesrather than strips in such situations may bedesirable.
Winter night-roosts are of particular concernin this ecoprovince because so many eaglesare concentrated here in winter (Farr andDunbar l988) and are expected to use com-munal roosts. Some formerly used roostingareas have undoubtedly been affected by log-ging/land clearing activities, especially in theFraser Valley. Although some roosting areashave been located in the Georgia Depression(Teske l989; Cassidy 1985; Farr l987), othersundoubtedly occur, and many are likely to bethreatened by forest removal. In the FraserValley, comments by Farr (l988), with respectto conservation of communal roosts, are ofnote:
“Future conflicts between logging and main-taining coniferous roost sites may be minimal
40
in some areas because the roost trees aresituated on steep, unstable slopes or nearrock bluffs. In other areas where logging isfeasible, cooperation with forestcompanies may be needed to ensure thatadequate roosting habitat is maintained.Scott Paper Ltd. has set a commendableexample by taking the Carey Roost out oftheir cut block boundaries to preserve it forfuture eagle use. As no other communal nightroosts have been located within 5 km of thisroost, it is a very important site for the eaglesthat forage along the Fraser River. It is alsoBritish Columbia’s first protected communalwinter night roost for Bald Eagles.”
3. Foraging habitat
Contamination of food sources and loss offoraging habitat are potential impacts that areboth of greater concern here than in any otherecoprovince. Within the ecoprovince, themost seriously affected locations are urbanwaterfronts and intertidal/inshore habitatsadjacent to pulp mills. Loss of habitat due toforeshore development involves a relativelysmall amount of total shoreline in theecoregion, but is steadily increasing. Increas-ingly stringent emission standards for pulpmills should arrest, and hopefully reverse,contamination of Bald Eagle foods in thisarea; however, cumulative pollutant loadsentering the Gulf of Georgia from the entireFraser River watershed and from HoweSound, and possibly Puget Sound, are of longterm concern.
Human harvest of eagle food resources, suchas herring and salmon, though probably moreintensive here than in other ecoregions, is ex-pected to have little future impact on eaglesas long as sustained yield management ispracticed.
Coast and Mountains Ecoprovince —
l. Nesting trees
Logging prior to l950, largely A-Frame andhand-logging operations, were localized andselective, leaving many poor quality trees un-cut and available for nesting eagles. Sincel950, clearcut logging has become wide-spread, especially in the southern half of theecoprovince, and on the Queen Charlotte Is-lands. Extensive clearcuts, especially those tothe shoreline, have probably reduced breed-ing populations in local areas.
With respect to Coastal Western Hemlockforests on islands in the Queen CharlotteSound-Johnstone Strait area, Morgan et al.(l985) note that avian species in lifeform 12(which includes the Bald Eagle)...
“prefer to build their nests on large branchesin tall trees. The removal of trees borderinglakes and marine coasts has undoubtedly re-duced the number of potential nest sites.”
Hodges et al. (l984) surveyed about 9% ofthe British Columbia coast in l980, and esti-mated that 21% of the coastline south ofCape Caution (including the GeorgiaDepression), and l0% of that to the north wasdisturbed habitat with no old-growth treespresent. No active nests were found in thosedisturbed areas. This provides a rough esti-mate of the extent of nesting habitat loss onthe Coast up to l980. Further logging couldincrease those percentages, although it is nowcustomary to leave shoreline and streamsidestrips of old growth, and to identify and pro-tect trees with eagle nests in them.
Future trends depend on the extent and suc-cess of such programs. It is possible that con-siderable remaining old growth could be
41
removed without further reducing the breed-ing population if presently used trees, andsome to replace them when they die, are leftin place. This assumes that nest trees innarrow strips, or isolated in logging slashes,are as acceptable to eagles as they were priorto logging; a subject that requires more study.It is possible that breeding populations couldeventually be increased in areas where noold-growth specimens presently occur if stra-tegically located second-growth trees orsmall groups of trees are allowed to advanceto old-growth status. However, this couldtake 200 years or more to occur.
In any event, logging is expected to proceedindefinitely throughout most of thisecoprovince, to continue to reduce theamount of potential nesting habitat available,and to restrict the choices available to eaglesfor nest site selection. This seems likely tocause a continued, gradual decline in breed-ing abundance, the extent of which is difficultto predict or to measure.
Some protected habitat occurs in NationalParks (Pacific Rim; South Moresby Reserve),in Provincial Parks and Recreation Areas(Brooks Peninsula, Cape Scott, Hakai;Fjordland, Naikoon, and several smallerunits), Ecological Reserves (most of theseabird islands), and forest company orMinistry of Forests Recreation Sites. Theseencompass less than l0% of the ecoregioncoastline, but include some of the most pro-ductive nesting habitat.
In addition, the windswept outer coasts ofVancouver Island, the Queen Charlottes, andislands along the northern Mainland Coasthave tree stands that are suitable for eaglenesting but not for logging. Hodges et al.(l984) estimated that l6% to l8% of theBritish Columbia coastline supported natu-
rally stunted “scrub trees” typically under 20m in height. These contained l8% to 27% ofthe active nests they found on the coast.Lands having reserve status, supporting non-merchantable timber, or inoperable due toslope steepness or other factors might com-prise 25% to 30% of Bald Eagle nestinghabitat in this ecoprovince.
Clearing for settlement and related purposeshas removed a very small proportion of nest-ing habitat in the ecoprovince, and this situa-tion is expected to change very little in thefuture.
2. Perching and roosting trees
Perch trees, like nest trees, have been, andwill continue to be, lost due to logging. Sincelarge numbers of eagles winter here, commu-nal night-roosts are expected to occur nearmajor winter food concentrations, such assalmon and eulachon spawning streams. Lo-cations of these roosts are largely unknown;however, many are probably vulnerable tologging activity.
3. Foraging habitat
Contamination of food sources is a very lo-calized threat, but of concern where pulpmills or other industries occur (Squamish,Gold River, Port Alice, Kitimat, PrinceRupert). Loss of feeding habitat is of minorconcern, and not expected to increase signifi-cantly. Human harvest of eagle foods is wide-spread, but not felt to have reduced eagleabundance, and not likely to be of future sig-nificance.
Dry Southern Interior Ecoprovince —This is the second most heavily settledecoprovince in British Columbia. There isconsiderable agricultural development along
42
the valley bottoms and logging on adjacentuplands. Eagle nesting habitat occurs alongmajor lakes and rivers in the valley bottomsand around some lakes on the adjacent pla-teau. Winter habitat is mostly associated withthe Thompson River and large lakes.
1. Nesting trees
Logging may be a threat around lakes on theOkanagan and Shushwap Highlands andThompson Plateau; however, the number ofnest sites involved is probably low. Canningset al. (l987) noted that eagles “still nestaround smaller mountain lakes east and westof the (Okanagan) valley,” but suggested thatthe nesting population along the main valleylakes had declined in recent decades due tohuman persecution and destruction of nesttrees. Logging on the uplands, and expansionof settlement and agriculture in the valleys,are expected to continue to reduce nestinghabitat in the ecoprovince.
2. Perching and roosting trees
Continued loss is expected for reasons men-tioned above; however, the over-all impactshould be minor.
3. Foraging habitat
Contamination of food sources, for examplefrom agricultural pesticides, is more likelyhere than in other parts of the Interior, al-though specific examples are lacking. Loss ofaquatic foraging habitat has probably beenminor, and should remain so. Road-killedanimals, livestock yards, and garbagedumps probably result in greater food avail-ability in winter than in pre-settlement times.
Southern Interior Mountains Ecoprovince—
1. Nesting trees
In this mountainous region it appears thatmost known nests are along valley bottoms(Campbell et al. l990), and that the best habi-tats are wetland complexes along the Colum-bia and Kootenay Rivers (Forbes and Kaiserl984). Nest trees along the ColumbiaMarshes and at Creston Valley are largelycottonwood, although this may not be true forthe entire region.
Hydro dams (Libby, Mica, Revelstoke, Ar-row, Duncan) have flooded considerablenesting habitat in this region; further losses ofthis kind are not probable. Although someeagles nest along the reservoirs, it seemslikely that these steep-sided fluctuatingwaterbodies are less suitable for eagles thanthe floodplains they have inundated.
Logging is widespread in the region, and un-doubtedly has removed some potential nest-ing habitat, and will continue to do so. Landclearing for settlement and agriculture hasaffected small areas, but often has an impacton floodplain cottonwood stands; minor butcontinuing losses can be expected. Smelteremissions have reduced tree cover in the Trailarea.
Although these combined factors have re-duced the extent of old-growth forest in theregion, some acceptable nest trees remain inmost areas, and it is probable that forest re-moval has had little effect on the total breed-ing population.
2. Perching and roosting trees
Continued loss is expected for reasons givenabove, however the long-term impact shouldbe low.
43
3. Foraging habitat
Reservoir flooding has caused a loss ofriverine and wetland feeding habitat in somevalleys, and this has probably reduced the re-gional nesting population slightly. Wetlanddevelopments, such as at Creston Valley, havehad a positive effect (Forbes and Kaiserl984). Contamination of food is a potentialthreat in very restricted areas like Castlegar-Trail and Skookumchuck. The winter carry-ing capacity of the region has likely beenimproved through availability of fish belowpower dams and traffic-killed ungulatesalong highways.
Central Interior Ecoprovince—
l. Nesting trees
Logging is widespread on the Interior Plateauand threatens nesting habitat along somelakes, wetlands, and rivers. Clearing for agri-culture and settlement are of little concern.Sufficient nest trees probably remain to main-tain the historical breeding population; how-ever, this situation could change.
2. Perching and roosting trees.
Availability of perching/roosting trees isprobably not a problem for the foreseeablefuture.
3. Foraging habitat
Flooding by the Nechako Reservoir removedsome valley bottom habitat, but the impact ofthis on eagle nesting abundance is notknown. Historical loss of wetlands, largelydue to agricultural land improvement,amounts to only about 2% of total wetlandarea (McKenzie l983). Wetland develop-
ments, like Chilanko Marsh, should improveforaging habitat in restricted areas. Loss offoraging habitat should have had a negligibleimpact on eagles in the ecoprovince as awhole, and the future rate of loss should bevery slow.
Sub-Boreal Interior Ecoprovince —
1. Nesting trees
Logging is also widespread in this region andis the major threat to nesting habitat. Clearingfor agriculture and settlement are of concernin the Vanderhoof-Prince George-Quesnelarea, especially along rivers and aroundlakeshores. Enough nest trees probably re-main to support the historical nesting popula-tion, although local exceptions could occur.Gradual loss of nesting habitat is expected tocontinue.
2. Perching and roosting trees
Availability of perching and roosting treesshould be of little concern for the foreseeablefuture.
3. Foraging habitat
Flooding by the Williston Reservoir removedsome valley bottom habitat, but the impact ofthis on nesting abundance is not known. Hy-droelectric developments like Kemano Com-pletion, if they affect fish abundance, couldalso affect eagles. Contamination of eaglefoods is a possibility near pulp mills (Mac-kenzie, Prince George, Quesnel), although noadverse effects are currently known. To date,impacts on foraging habitat have probablyhad little effect on nesting season or autumnpopulations. So few eagles winter here thatwinter foraging habitat is not of concern.
44
Northern Boreal Mountains Ecoprovince —Few Bald Eagles nest in this region, and thehabitats of those that do, or that migratethrough the area in spring or fall, appear to bequite secure at present and for the foreseeablefuture. There is essentially no winter habitatin this area.
Boreal Plains Ecoprovince —
l. Nesting treesMuch land has been cleared for agriculture,but this has likely had little effect on nestingeagles. Enough trees apparently remainaround the few lakes that have sufficient foodresources to support nesting eagles; i.e.,Charlie, Cecil, and Boundary Lakes. Mostknown nesting in this ecoregion (six to tensites) is in cottonwoods along the PeaceRiver between Hudson’s Hope and the Al-berta border (Siddle l990). Some of thosenest sites would be lost if the Site C Dam isbuilt. Some logging occurs in the region butis not a known threat to nesting habitat. Bar-ring hydro development, the supply of nesttrees appears to be relatively secure.
2. Perching and roosting trees
Loss of perching and/or roosting trees is not asignificant concern.
3. Foraging habitat
Impacts on foraging habitat are mostly ofconcern for migrant and nesting eagles. Somedrainage of wetlands that formerly attractedmigrant waterfowl and eagles has already oc-curred (Siddle l990), and the trend is ex-pected to continue. Construction of the Site CDam would flood foraging habitat used byseveral nesting pairs. The reservoir would
provide less suitable habitat than presentlyoccurs. Foraging at Charlie Lake could be in-terfered with if cottage development contin-ues. Hydro dams (W.A.C. Bennett and SiteOne) have enhanced winter habitat by pro-viding fish that pass through turbines or overspillways and by maintaining year-roundopen water for some distance downstream.
Taiga Plains Ecoprovince — Habitats of thefew eagles that nest in or migrate through thisregion are probably quite secure. No winterhabitat is present.
2.2.7 Habitat trends
As discussed in Section 2.2.6 above, trends inhabitat loss vary considerably from place toplace in British Columbia. Significant perma-nent reduction of nesting populations hasprobably only occurred in urban areas likeGreater Vancouver and Victoria, but nestinghabitat loss is accelerating in adjacent areason the southeast coast of Vancouver Island,the Gulf Islands, and in the Fraser Valley. Inthose areas, the current rate of change is atleast moderate and is of concern because thelosses are more or less permanent.
Nesting habitat is also changing rapidly incoastal areas subject to clear-cut logging;however, this is of less concern because nesttrees are usually spared, many sites are non-operable, and, as a last resort, some second-growth trees can be allowed to advance toold-growth status in the future.
Impacts on feeding habitat have probablyonly been significant in the Georgia Depres-sion, and even there the current rate of degra-dation would be rated as slow.
45
2.2.8 Habitat status and protection
It is probable that about 90% of BritishColumbia’s Bald Eagle nest sites are onCrown Lands. This affords the opportunityfor government to institute management andprotection programs that will control forestharvesting impacts on nesting populations. Itis estimated that less than l0% of nest sitesare currently inside protected areas like parksor Ecological Reserves. Nests in such re-serves are mostly along the coast. Many nesttrees in the Georgia Depression are on privateland.
The current level of nest tree protection is notadequate on either Crown or private land.Leaving only a single nest tree in clear-cutlands will not provide for long term popula-tion maintenance. The same is true for landscleared for settlement.
Most critical habitat, particularly on Crownlands, can probably be protected by meansother than land acquisition. Some landacquisition would be desirable in the GeorgiaDepression, but waterfront lands here arevery expensive. However, acquisition of stra-tegic parcels having old-growth trees may bejustified where multiple values are involved;i.e., parkland, greenbelt, and use by a varietyof wildlife species that need old growth.
3.1 North America
3.1.1 Breeding range
The present breeding range of the Bald Eagleextends from the southern Brooks Range inAlaska, east through most of the Yukon,northwestern and southern Mackenzie Dis-trict, across northern Saskatchewan andManitoba, central Ontario, central Quebec,Labrador and Newfoundland; south throughthe Commander and Aleutian Islands, andalong the coast to Baja and Sonora Mexico;and along the Gulf Coast of southeasternTexas to Florida. It is absent as a breedingbird through much of the Great Basin andmost of the prairie and plains region, andvery locally distributed in the interior of thelower 48 states (A.O.U. l983).
The former breeding range evidently in-cluded “every state except Hawaii” (Brownelland Oldham l983), although documentationfor this is poor. In the United States, the nest-ing distribution receded through the l9th and20th centuries, and now most active nests arerestricted to the Great Lakes states (Michi-gan, Minnesota, Wisconsin), Florida, the Pa-cific Northwest (Oregon, Washington), theChesapeake Bay area, and coastal New Eng-land (mostly Maine), with scattered nestselsewhere (Snow l973; Marshall andNickerson l976).
3.1.2 Winter distribution
Major wintering areas include the northwestPacific Coast from the Aleutians to PugetSound, and the central interior of the UnitedStates. Millsap (l986) reported that winterconcentrations occur on most major westernUnited States river systems. The majorityare associated with either the Mississippi or
3.0 DISTRIBUTION
The breeding range of the Bald Eagle is re-stricted to North America, although non-breeding birds have wandered to the Siberiancoast, Ireland, and Puerto Rico (A.O.U.l983).
46
Missouri rivers and tributaries; other impor-tant river systems are the Arkansas, Colum-bia-Snake, Colorado, Platte, Illinois,Klamath, Red, Skagit, Rio Grande-Pecos,Tennessee, and Sacramento. Concentrationareas in the east are associated with severaltributaries of Chesapeake Bay, the DelawareRiver in New York, and Quabbin Reservoir inMassachusetts.
The former winter distribution is not reliablyknown, but probably differed little from thecurrent winter range.
3.2 Canada
3.2.1 Breeding range
In Canada, Bald Eagles presently nest fromcoast to coast (Figure 4). In the south, theyare absent from most of southern and centralAlberta and Saskatchewan, and southwesternManitoba. To the north, they are found acrossall but the extreme northern edge of theYukon, to the Mackenzie delta, and thencesouth of a line running from just north ofGreat Bear and Great Slave lakes to the ex-treme northeast corner of Saskatchewan; eastto the Churchill area of Manitoba, and thensouth around Hudson Bay and James Bay,and northeastward across central Quebec andsouthern Labrador, including all of New-foundland and the Maritime provinces. Thenorthern limit of the range east of James Bayis poorly known (Godfrey l986). East of theRockies there are few significant populationsnesting south of the Canadian Shield; to thenorth the population appears to be confinedby a temperature or seasonality limit.
The largest known populations of breedingeagles are found along the coast of BritishColumbia and across the lake-studded BorealForest region of Saskatchewan, Manitoba,
and northwestern Ontario. Smaller and morescattered populations occur across the Yukon,interior British Columbia, southwest Mac-kenzie, Alberta, and from southern Ontarioeastward to the Maritimes (Brownell andOldham l983).
The former Canadian breeding range is be-lieved to have been quite similar to thepresent distribution, but was probably morecontinuous in areas that are now heavily set-tled and support few breeding pairs. This in-cludes southern Ontario and Quebec, andparts of the Maritime Provinces.
3.2.2 Winter distribution
With the exception of eagles that winteralong the entire coasts of British Columbiaand the Maritimes, most Canadian Bald Ea-gles winter in the United States. Small num-bers also winter in southern interior BritishColumbia (Figure 4), and scattered individu-als also occasionally winter across southernCanada, particularly where open water ispresent (Brownell and Oldham l983; Godfreyl986).
Power dams and thermal plants now allow afew eagles to winter beyond their formerrange; however, the number of birds involvedis small.
3.3 British Columbia
3.3.1 Breeding range
The breeding range of Bald Eagles in BritishColumbia essentially includes the wholeprovince (Campbell et al. l990); however,nesting abundance varies greatly from placeto place (Figure 5). Nesting abundance ishigh on the coast where 30 to 70 adults, andeight to 20 or more active nests, per l00 km
47
Fig
ure
4.
Th
e b
reed
ing
an
d w
inte
rin
g d
istr
ibu
tio
n o
f th
e B
ald
Eag
le in
Can
ada.
(A
dap
ted
fro
m B
row
nel
l an
d O
ldh
am 1
983)
.
48
Fig
ure
5.
Th
e d
istr
ibu
tio
n a
nd
rel
ativ
e ab
un
dan
ce o
f n
esti
ng
Bal
d E
agle
s in
Bri
tish
Co
lum
bia
.
49
of shoreline have been reported in various ar-eas (Table 10). These numbers are mostlybased on single aerial surveys and are there-fore conservative. Observations made atseabird nesting islands (Vermeer et al. l984;Rodway et al. l988), though not directlycomparable because most surveys were byboat, suggest that seabird islands have nest-ing densities higher than the coastal average.This is also suggested by data of Harris(l978) for islands on the east coast ofMoresby Island.
In the Interior, nesting densities along themost productive rivers may be similar to thecoast (Table 10), but such habitats are not ofwidespread occurrence. Many high-gradientand high-elevation rivers support no nestingeagles, and nesting is not known to occurabove 1370 m elevation. Medium-sized lakesappear to have relatively low nesting densi-ties, and this is probably also true for largelakes and reservoirs. Complexes of smalllakes and wetlands, such as occur in theCariboo region, also appear to support many
Table 10. Linear frequency of adult Bald Eagles and eagle nests along shorelines in BritishColumbia.1
Location and source Shoreline Adults/ Active nests Total nests/length (km) l00 km /l00 km l00 km
Marine shorelinesNorth of Cape Caution 1360 39 9 15 (Hodges et al. l984)
South of Cape Caution 1250 37 8 - (Hodges et al. l984)
Gulf Islands 796 63 12 15 (Vermeer et al. l989)
Barkley Sound 573 29 9 - (Vermeer and Morgan l989)
Quatsino Sound Area (TFL6) 209 - 17 36 (Lueke-Joyce, unpubl)
Queen Charlotte Islands 391 70 19-29 36 (Harris l978)
Freshwater habitatsLower Fraser/Harrison rivers l00 - 12 - (Farr l988)
Nechako R. above Stuart R. 176 - 9 - (Blood and Anweiler unpubl.)
Columbia R. (Athalmer-Donald) 162 - 9 - (Blood and Anweiler unpubl.)
Peace R. above Moberly R. 81 - 4 - (Blood and Anweiler unpubl.)
Cheslatta/Murray Lakes(Blood and Anweiler unpubl.) ll5 - 4 -
Nanika/Kidprice/Stepp Lakes 85 - 2 - (Blood and Anweiler unpubl.
1 All surveys were by aircraft, except Harris 1978, which was by boat.
50
breeding eagles (Blood and Anweiler l990b);however, nests per kilometre of shorelinecannot be reliably determined for such areas.
3.3.2 Winter distribution
It is probable that over 90% of Bald Eagleswintering in British Columbia do so alongthe coast. This includes both the marine envi-ronment and river valleys west of the CoastRange. The Gulf of Georgia may have thehighest winter concentration (Farr andDunbar l988). Wintering in the Interior is al-most entirely along the bottoms of major val-leys in the southern third of the province(Figure 6).
4.0 POPULATION SIZE ANDTRENDS
4.1 North America
4.1.1 Population size
Over the past 50 years, various individualsand agencies have attempted estimates of theNorth American Bald Eagle population(Lumley l939; Sprunt and Ligas l964; Braunet al. l975; Lincer et al. l979; Evans l982;Gerrard l983; Millsap l986). These were usu-ally based on estimates of the number ofbreeding pairs in a state or region, or esti-mates of numbers wintering in the lower 48states. The large numbers in British Colum-bia and elsewhere in Canada were often notincluded. Braun et al. (l975) estimated theNorth American population in the mid-70s at35 000-60 000, but gave no information ondistribution or how they arrived at thatnumber.
Breeding population estimates are availablefor only portions of the species range and donot provide a basis for estimation of the total
population. Winter counts, when eagles areconcentrated in more observable southernand coastal locations, presently provide thebest estimates of total population size.Gerrard (l983) analysed Christmas BirdCount data for the entire continent for theyears l955 through l980. He arrived at anestimate of approximately 70 500 BaldEagles as of l980, with l9 000 in Alaska, 30000 in Canada (28 500 of these in British Co-lumbia), and 21 500 in the lower 48 states inmid-winter. More recent estimates based onmid-winter eagle counts; i.e., 14 000-22 000in the lower 48 states (Millsap l986) and 20000 to 30 000 in British Columbia (Farr andDunbar l988), tend to support Gerrard’s re-sults.
Based on a ratio of one-third immature andtwo-thirds adult eagles, the population of 70000 should contain about 47 000 adults. Al-though this could translate to 23 500 breed-ing pairs, the actual number of active nestsites would be somewhat less because manyadults do not breed, especially where thenesting habitat is saturated (Hansen andHodges l985).
4.1.2 Population trends
The long term trend in Bald Eaglepopulations is hard to document because his-torical information is sparse. However, it iswidely accepted that there has been a declinein numbers across most of the continentsince the advent of European settlement,particularly in the eastern and mid-western United States (Snow l973; Griffinet al. l982). Review of available historicalinformation by Lincer et al. (l979) tends tosupport this contention. Beebe (l974) be-lieved that populations along the BritishColumbia and Alaska coasts were littlechanged from prehistoric times, although the
51
Fig
ure
6.
Th
e d
istr
ibu
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n a
nd
rel
ativ
e ab
un
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ce o
f w
inte
rin
g B
ald
Eag
les
in B
riti
sh C
olu
mb
ia.
52
large numbers killed in Alaska over the firsthalf of this century under the bounty systemundoubtedly had some impact (Alcorn l975).
In the l950s, a rather abrupt and drastic de-cline in Bald Eagle populations and produc-tivity was observed in many populations inthe eastern part of the continent, which wascorrelated to the widespread use at that timeof the pesticide DDT. (Snow l973; Brownelland Oldham l983). Populations across muchof the northern and western parts of thecontinent appeared largely to escape thisproblem. However, populations in Californiaexperienced a similar decline due to majorDDT producers in Los Angeles dischargingtoxic waste into the ocean (R. Davies, pers.comm.). In the late l960s, Sprunt (l969) ex-amined productivity data for variouspopulations across the continent and con-cluded that populations in Alaska and BritishColumbia appeared to be stable, while thoseeast of Lake Erie, along the Atlantic and Gulfcoasts, and over much of Florida, were de-clining due to low reproductive rates. Fyfe(l977) stated that Canadian populations ap-peared to be stable in the mid-l970s.
Based on his analyses of Christmas BirdCount data, Gerrard (l983) estimated thatBald Eagles along the east coast and parts ofFlorida in l980 were at about one-half to one-third their l955 level. He found that in thecentral and interior western states, winteringeagles had increased by a factor of two orthree over the same period. Trends for thewest coast and Alaska were less clear. Healso noted that where populations had de-creased, the trough of the decline had oc-curred about l970, and that an upward trendwas evident since. Swenson et al. (l986) re-ported an exponential increase in theYellowstone nesting population from l97l tol982. Swenson (l983) analysed a wide range
of data, and concluded that populations nest-ing across the boreal forest regions west ofOntario had increased steadily since thel930s. Hansen and Hodges (l985) estimatedthat Bald Eagle densities in southeast Alaskawere double those of l941.
Grier also indicated that Bald Eaglepopulations appear to be increasing through-out much of their range in the east, followingthe reduction in productivity observed in thel960s, and ‘70s (Grier l982). Populationshave also increased in the lower peninsula ofMichigan, northwestern Ontario and atChesapeake Bay in recent years (Brownelland Oldham l983).
4.2 British Columbia
4.2.1 Population size
Breeding population — The number ofadult Bald Eagles in British Columbia wasrecently estimated at l5 000, with about4000 along the north coast, 5000 along thesouth coast, and another 6000 scatteredthroughout the Interior (Davies l985). Esti-mates for the coast were derived from aerialsurveys of a number of stratified randomplots (Hodges et al. l984); that for the Interiorwas extrapolated from meagre survey datafor major river systems. The coast populationestimates, being based on a single aerialsurvey, are probably quite conservative.Based on the estimate of l5 000 adults, 7500breeding pairs could occur in the province.However, a variable percentage of the adultpopulation is made up of non-breedingadults, therefore the number of active nestsmay be well below 7500. Hodges et al. (l984)estimated that 56% of adult eagles on theBritish Columbia coast were not breeding,which leaves a potential 3960 breedingadults, or l980 pairs. The percentage of non-
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breeding adults in Interior populations isprobably lower than that in the rich coastalenvironment, perhaps closer to the l9% non-breeding adults in Saskatchewan populations(Gerrard and Bortolotti l988). This wouldleave approximately 2400 breeding pairs inthe Interior, and a total of about 4500 breed-ing pairs in the province. W.T. Munro (inBrownell and Oldham 1983) estimated theprovincial population as 6000 to 7000 breed-ing pairs.
Immature eagles present during the breedingseason make up about 27% to 33% of thepopulation (Davies l985; Gerrard andBortolotti l988), which would account for anadditional 6000 eagles, bringing the totalBritish Columbia population during thebreeding period to about 21 000 birds (Table11).
Winter population — The total number ofBald Eagles wintering in the province islikely somewhat larger than the summeringpopulation, due to the year’s production ofyoung, and some immigration from Alaska(Hodges et al. l987; Campbell et al. l990).
However, some eagles from the interior ofBritish Columbia also move south to the U.S.in winter. Based on an analysis ofChristmas Bird Count data, Gerrard (l983)estimated the mid-winter population inBritish Columbia in l980 was about 30 000,with 24 000 of these found in the southwestquarter of the province. Based on mid-wintersurveys in recent years, Farr and Dunbar(l988) estimated the wintering populationat 20 000 to 30 000 eagles, of which slightlymore than one-third were immatures.
4.2.2 Population trends
As for North America in general, historicaltrends in British Columbia are difficult todocument. In the extreme southwest cornerand southern interior valleys, settlement andforest clearing may have caused somereduction in the breeding population sincethe pre-settlement era. Beebe (l974) believedthat populations along the largely unsettledcoast had changed little if any since prehis-toric times. Recent surveys and re-surveys ofpopulations along the south coast area haveindicated stable or increasing populations of
Table 11. Estimates of the abundance of adult and immature Bald Eagles in British Columbiaduring the nesting season.
Breeding status Coastal1 Interior2 Total
Adults - Breeding 3960 4800 8760 - Non-breeding 5040 l200 6240 - Total 9000 6000 15 000Immature 3400 2570 5970Total eagles 12 400 8570 20 970
1 Adult data from Hodges et al. (1984).2 Total adult estimate from Davies (1985). Non-breeders estimated to make up 20% of the adult population. Immatures esti-
mated to comprise 30% of total eagle population. “Interior” population includes non-marine habitats west of the summit ofthe Coast Range.
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breeding eagles since the l960s (Hancockl964; Trenholme and Campbell l975; Retfalvil977; Vermeer et al. l989; Vermeer andMorgan l989). In the Gulf Islands, spring sur-veys by Trenholme and Campbell in l974found no change from the numbers found byHancock in l963 and l964. Vermeer et al.(l989) surveyed this area again in l987, andfound an increase of 30%. Vermeer andMorgan (l989) surveyed the Barkley Soundarea in l988, and found numbers had notchanged significantly since Retfalvi surveyedthe area in l97l-l973.
Recent surveys in Washington (l980-l985)have also found populations there to be in-creasing (McAllister et al. l986). Hansen andHodges (l985) found that eagle densitiesalong the southeast coast of Alaska had ap-proximately doubled since l941, possibly as aresult of the elimination of the bounty systemin the l950s which was responsible for thedeath of many eagles. The high numbers ofnon-breeding adults observed along thecoasts of British Columbia and southeastAlaska may be an indication that the avail-able breeding habitat is saturated with territo-rial breeding pairs (Hodges et al. l984;Hansen and Hodges l985).
Pacific Northwest eagles seem largely tohave escaped the heavy pesticide contamina-tion that was believed to be responsible fordeclines in populations and productivity ofBald Eagles in eastern North America. How-ever, continued clearcut logging of old-growth forests and pollution of coastal watersby dioxins, furans, and other chemicals mayhave negative impacts on Bald Eagles in fu-ture, and this should be monitored. Increasingrecreational use of Interior lakes and riversmay also have negative impacts on nestingBald Eagles.
5.0 LEGAL PROTECTION
5.1 United States
In l940, the United States Bald Eagle Protec-tion Act was passed and it became illegal toharm Bald Eagles and their nests and eggs.This Act did not apply in Alaska until state-hood was granted in l959. In l953, the territo-rial Bald Eagle bounty law in Alaska wasrepealed, thereafter allowing eagles to bekilled only when causing damage.
The United States Endangered Species Act ofl966 extended protection to include habitat.Under this Act, only the Southern Bald Eaglewas listed as Endangered, but Bald Eaglenest sites on National Wildlife Refuges wereclosed to the public during the nesting sea-son, an order was issued prohibiting timbercutting within l/2 mile of trees containingBald Eagle nests, and provisions were madeto protect future nesting habitat. This Act wasamended and broadened under the Endan-gered Species Conservation Act of l969. Inl978, due to the difficulties in distinguishingbetween Northern and Southern Bald Eagles,the entire species was listed as Endangered inthe lower 48 states (except in Washington,Oregon, Minnesota, Wisconsin, and Michi-gan, where it was listed as Threatened); theAlaskan population was excluded. In additionto these Federal laws, the Bald Eagle has alsobeen extended various degrees of protectionunder State law in all states but Hawaii(Snow l973; Brownell and Oldham l983).
While British Columbia Bald Eaglepopulations appear to be large and eitherstable or increasing at present, future trendsare difficult to anticipate.
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5.2 Canada
Contrary to published reports (Lincer et al.1979), the Bald Eagle is offered no directprotection in Canada under Federal law, otherthan the prohibition of import or export ofeagles and eagle parts under the Conventionon International Trade in EndangeredSpecies of Wild Fauna and Flora (CITES)convention, administered under the Exportand Import Permits Act. Raptors, includingthe Bald Eagle, are not included in theMigratory Birds Convention Act of l9l6(C.W.S. 1978). Under the British-NorthAmerican Act (B.N.A.), each province hasjurisdiction over the wildlife within its bor-ders, and various laws have been enacted inall provinces offering some protection to theBald Eagle. Two provinces, Ontario and NewBrunswick, have passed Endangered Specieslegislation, and the Bald Eagle is listed asEndangered in both provinces (Brownell andOldham l983).
5.3 British Columbia
In British Columbia, Bald Eagles are pro-tected by the Wildlife Act, under which it is il-legal to harm or molest Bald Eagles, theirnests and eggs. Recent amendments now pro-tect the nests, whether or not they are occu-pied. Other Acts, both Provincial andFederal, indirectly offer some protection toBald Eagle habitat; including the provincialPesticides Control Act, which controls the useof pesticides; the Waste Management Act,which regulates water quality and dischargeof pollutants; and the Park Act and Ecologi-cal Reserves Act, which protect some nestinghabitat.
Munro (l982) stated that no legislation existsto protect roost trees, or potential nesting androosting habitat on lands outside of
designated reserves, although trees havingnests in them now have protection under theWildlife Act.
Protection of areas around actual and poten-tial nest trees on Crown lands managed fortimber harvest is a major need. Although theBritish Columbia ministries of Forests andEnvironment, Lands and Parks have policiesto designate and protect from cutting “wild-life trees”, and some forest companies nowcarry out eagle nest surveys and refrain fromcutting known nest trees, a more comprehen-sive province-wide program of nesting habitatprotection is needed.
6.0 LIMITING FACTORS
6.1 Causes of RegionalPopulation Declines
Historically, three major factors are consid-ered to have caused significant regionaldeclines in Bald Eagle populations in NorthAmerica: shooting mortality, pesticide con-tamination, and habitat loss. The Alaskaneagle bounty severely reduced eaglepopulations there in the first half of thecentury, but populations have since recovered.Indiscriminate shooting may have also af-fected populations in other areas (Beebel974). Pesticide contamination in easternNorth America, primarily from DDT and itsmetabolites, caused drastic declines from theGreat Lakes to Florida between l950 and thel970s. A similar occurrence took place inCalifornia. Forest spraying with DDT alsoaffected some western populations (Swensonet al. l986). This problem, in which popula-tion declines resulted from reproductive fail-ure, has been extensively documented (Spruntet al. l973; Brownell and Oldham l983) andwill not be discussed in detail here. Sincewidespread use of DDT was banned in
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Canada and the United States in the l960s,Bald Eagle populations in many areas havebegun to increase (Grier l982). Permanentloss of habitat, particularly nesting habitat,has undoubtedly reduced some eaglepopulations from Southern Ontario toFlorida, and in the midwest states. This hasbeen a gradual process over a period of 200years, and is not well documented. In con-trast to direct shooting and pesticide contami-nation, there is little chance that populationlosses caused by permanent habitat alienationcan be regained.
6.2 Direct Mortality
6.2.1 Natural mortality
In pre-settlement times, Bald Eagles un-doubtedly died of a variety of natural causes,including parasitism and disease, intra-specific aggression, starvation, predation onnestlings, destruction of nests by storms, andvarious accidents. These factors still occurtoday, plus a variety of hazards attributable tohumans. Nestlings have been reported to diefrom sibling competition, from nest destruc-tion caused by storms, and from falling out ofnests. Black Bear predation may also occur(McKelvey and Smith l979), but is undoubt-edly rare. Natural mortality of nestlings is notconsidered to be a significant limiting factor.
Natural mortality factors in wild juvenile andadult eagles are poorly known. Starvation andaccidents are undoubtedly important for im-mature eagles, while disease and degenera-tive processes, sometimes coupled withmalnutrition, are probably important for thelong-lived adults.
Although most eagles submitted to rehabilita-tion centres or pathology laboratories suffer
from human-caused conditions, a few casesinvolve natural agents. Live Bald Eaglestreated by Redig (et al. l983) included casesof developmental anomalies, cataracts, respi-ratory disease, septic polyarthritis, porcupinequill damage, and fighting injuries. Majornatural morbidity and mortality factors inBritish Columbia appear to include: fallingfrom the nest, colliding with various objectswhen learning to fly, intraspecific aggression,disease (including cardiac disease, asper-gillosis and avian pox), and starvation (K.Langelier, unpublished data).
6.2.2 Human-caused mortality
The relative importance of various human-re-lated mortality factors appears to vary fromplace to place. Until at least l980, shootingwas the major known cause of mortality inthe United States, although losses to thiscause have been steadily declining in recentyears. Accidental trapping is still a significantcause of death, particularly where Muskrattrapping is common. Collisions with cars,trains, overhead wires, and antennae appearto be taking an increasing toll in settled areas.A related problem, electrocution by powerlines, is also of fairly widespread occurrence.Eagles have also died after becoming tangledin protective netting at fish-rearing facilities,in fishing gear, and in barbed wire.Poisonings of various kinds are also preva-lent, and result mainly from ingestion ofpoison bait set out for predator or pest con-trol. Plumage fouling by oil and sewagehave also been reported (Schmeling andLocke l982; Redig et al. l983; Fraser l985).
In British Columbia, the order of importanceof anthropogenic mortality causes is approxi-mately as follows: collisions with variousvehicles and objects, poisoning, electrocu-
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tion, shooting, trapping, and other accidentssuch as becoming tangled in nets, or plumagefouling (K. Langelier, unpubl. data). Leadpoisoning caused by ingestion of shot whenfeeding on waterfowl is the most frequentform of toxicosis in southwestern BritishColumbia (Langelier et al. l99l). Sub-clinicallead toxicosis, by affecting sensory percep-tion and coordination, may also predisposeeagles to many other kinds of mortality.Improper disposal of livestock carcasseseuthanized with barbiturates has resulted insome mortality. Carbofurans have beenidentified as a potential toxicity problem.
Some mortality factors, such as lead poison-ing, may decrease in the future as lead shot isphased out; others, such as vehicle collisionsand electrocution, may increase.
There is no doubt that human civilization hasintroduced many hazards with which eagles(and other wildlife) must contend, and newones will probably arise in the future. How-ever, the proportion of any eagle populationsuffering such losses on an annual basis, andthe over-all role of human-caused mortalityas a limiting factor, are not known. Atpresent, populations in most areas appear tobe maintaining their numbers in the face ofthis mortality.
6.3 Reproductive Failure
As noted earlier, reproductive failure causedby bioaccumulation of persistent chemicals,particularly organocholorine compounds, hasthe potential to cause population declines.This does not appear to be a major threatat present; however, continued monitoringis needed to assess the potential of indus-trial pollutants, such as dioxins and furans,for causing reproductive failure. These and
other related chemicals are known to occurin foods eaten by eagles on the BritishColumbia coast.
6.4 Disturbance
There is considerable debate about whetherhuman activities in the vicinity of nesting orforaging sites will adversely affect BaldEagles (see review by Fraser l985). There islittle doubt that serious disturbance, such asclimbing to nests during incubation, willcause eagles to desert their nests; however,this level of disturbance is rare. The usualkinds of disturbance do not cause direct mor-tality, and assessment of their effects is verydifficult.
Effects of disturbance on nesting eagles varygreatly with previous conditioning of thebirds. Some eagles have adapted to nesting inareas with much human activity; however,there is probably a limit to this. Eagles mayno longer nest in many urban areas becausesuitable trees are lacking, food resources nolonger occur, or disturbance levels are toohigh. Disturbance levels probably do limit thedistribution and abundance of nestingeagles in some built-up areas. Fraser (l985)reported that nests in Minnesota and Mary-land are further from human activity centresthan from random points.
Human activity frequently causes eagles tovacate feeding sites, both during the nestingand winter seasons. This is of particularconcern in winter, when the birds are in anegative state of energy balance. Frequentdisturbance of wintering eagles couldtheoretically reduce survivorship and havepopulation consequences (Stalmaster l983);however, real effects have not yet been docu-mented. Fraser (l985) concluded that
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“... human activities that chronically exceedthe limits of eagle tolerance may be consid-ered a form of habitat destruction. This is aparticularly insidious impact because there isno overt indication of the impact obvious tountrained or casual observers.”
Human disturbance may adversely affect afew eagles in localized situations in BritishColumbia, but is not presently thought to be asignificant limiting factor. However, distur-bance levels are expected to increase in thefuture and the situation should be monitored.
6.5 Limiting Factors
6.5.1 Food resources
The availability of food, together with theterritorial nature of nesting Bald Eagles, isthought to be the major factor presently limit-ing population increase. Nesting densities arehighest where food is abundant (e.g., coastalseabird islands), and low where it is not (e.g.,interior lakes). Increased food resources inareas having limited food would presumablyresult in higher nesting densities, thereforefood may be considered a limiting factor.Food availability in winter is probably alsoimportant, especially for immature eagles.
At present, there is no indication that BaldEagle food supplies in British Columbia aredecreasing, although factors such as intro-duction of predators to seabird islands, orover-fishing of rockfish or herring stocks,have the potential to adversely affect eaglepopulations. Human activities have actuallyresulted in many new sources of food foreagles, probably allowing some areas at someseasons to support larger populations thanwould otherwise be possible (see Section 2).
6.5.2 Nesting sites
Bald Eagles are generally precluded fromnesting where suitable nest trees are notpresent. The breeding range has shrunk insome parts of the United States where largeareas have been cleared for farming or otherpurposes. Loss of nesting trees to date hasprobably had a minor impact on the nestingseason carrying capacity of British Columbiafor Bald Eagles, although local reductions areexpected to have occurred in urbanized areasand on some clear-cut lands, and furtherdeclines of this nature are expected. Gradualloss of nesting habitat is expected to be themost significant factor affecting Bald Eagleabundance in British Columbia in the future.
7.0 SPECIAL SIGNIFICANCE OFTHE SPECIES
7.1 Status
The Bald Eagle is included on the 1993 BlueList of wildlife species prepared by the B.C.Ministry of the Environment, Lands andParks as part of its Provincial WildlifeStrategy, indicating that it is a sensitive orvulnerable species, or one for which there isinadequate information for evaluation.
In l970, the Bald Eagle was included on a listof Endangered Wildlife in Canada (Godfreyl970). It is currently listed as Endangered intwo Canadian provinces, Ontario and NewBrunswick. The Bald Eagle is currently listedas "Species Examined and Not Designated InAny Risk Category" by the Committee onthe Status of Endangered Wildlife in Canada(COSEWIC).
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In the United States, the Bald Eagle is cur-rently officially listed as Endangered in 43states, and as Threatened in five. It is notlisted as Endangered or Threatened inAlaska. The Southern Bald Eagle is listed asEndangered in the IUCN Red Data Book; theNorthern Bald Eagle is not listed by IUCN.The Bald Eagle is the only member of the ge-nus in North America, and is restricted toNorth America. Two related forms, theMadagascar Sea Eagle (Haliaeetusvociferoides) and the White-tailed Eagle(H. albicilla), are listed in the IUCN RedData Book, the former as Endangered and thelatter as Threatened.
7.2 Public Interest
“Wherever eagles occur common they areamong the best known of birds. They appearfrequently in the language and legends of an-cient peoples, and have often been chosen asnational emblems, since for size, powerfulflight, and fierce nature they have been cel-ebrated since earliest historic times.”(Oberholser l906).
On 20 June l792, the Bald Eagle was offi-cially adopted as the emblem of the UnitedStates of America, and since that time hasplayed a large part in the symbolism and cul-ture of that nation, as it did among the nativepeoples of the continent since time immemo-rial.
Bald Eagles are one of the best known birds,and attract many viewers and non-consump-tive recreational users to areas where theymay be seen. In recent years, several areas inthe United States have been set aside for BaldEagle use; towers, blinds, and camouflagedtrails have been built to accommodate view-ing without disturbing the birds (Spencer
l976). Bald Eagles have a great potential astourist attractions wherever they occur in anynumbers.
7.3 Economic Value
Bald Eagles have little economic value perse, although there is an illicit trade in feathersand parts for the manufacture of artifacts,which can be quite extensive. An estimated200-300 eagles were killed for feathers andother body parts over a three-year period end-ing in l983 at a roost in South Dakota(Gerrard and Bortolotti l988).
The negative economic value attributed to ea-gles in the past, through the supposed de-struction of livestock, gamebirds, and fish,has largely been discounted, although they dotake waterfowl in many areas. Depredationsof livestock are almost non-existent, althoughthere are a few documented cases.
Bald Eagles are an important component ofnature tours in many areas, and this value isgrowing steadily. British Columbia is wellsituated for viewing of nesting and winteringeagles by American visitors.
7.4 Species Security
With a total population approximating 70,000individuals and most regional populationsnow either stable or increasing, the Bald Ea-gle appears to be relatively secure as a spe-cies. Although designated as Threatened orEndangered over much of its geographicrange (all of the lower 48 states and two Ca-nadian provinces), the bulk of the populationoccurs in Alaska, British Columbia, and theboreal forest of western Canada, locationswhere habitat and populations seem to bequite secure. Current trends do not suggest
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any worsening of the present continentalstatus in the near future, although the long-term outlook is less optimistic. Increasinghuman populations, land development, andpollution are bound to have a gradual long-term impact on available habitat.
8.0 PROTECTION ANDMANAGEMENT
In the United States, where the Bald Eagleis considered to be Threatened or Endan-gered in all states except Alaska, and wherethe species enjoys a high profile as the na-tional emblem, management and protectionmatters have received considerable attention.These include intensive activities such ascaptive breeding, reintroductions to formernesting habitat, construction of artificial nestsites, artificial feeding of free-ranging birdswith non-contaminated food, and nest-watchprograms to prevent disturbance. None ofthose programs appear to rate immediateattention in British Columbia, although acertain amount of nest surveillance in settledareas could be worthwhile.
In the Pacific Northwest states, includingAlaska, much attention has been given toprotection of nesting and roosting habitatfrom logging impacts, and protection of bothnesting birds and winter concentrations fromhuman disturbance. Many findings there aredirectly applicable to British Columbia.
8.1 Inventory Needs
Although regional population densities andthe total number of eagles nesting and winter-ing in British Columbia are relatively wellknown, the exact location of most nesttrees and roosting sites has not been re-corded. One cannot manage and protect the
resource without this information. Locationsof most nests in southeast Alaska (Hodgesand Robards l98l), Washington (McAllister etal. l986), and Oregon (Isaacs et al. l983) arenow known, but similar data for British Co-lumbia are lacking. Location of all nests inBritish Columbia would be a mammoth un-dertaking, but could be phased over a periodof years, with earliest attention given to highpriority locations, such as coastal old growthdestined for logging. Several logging compa-nies are presently carrying out such invento-ries, and all should be required to do so,and to submit maps showing nest locations.This should also apply to Interior operators,who are logging lands adjacent to rivers andlakes. Provincial coordination of such a pro-gram is needed. Inventory is also needed onprivate lands, primarily in the Georgia Straitregion and southern Interior valleys. Identifi-cation and mapping of important winterroosts is also needed.
8.2 Protection Needs
8.2.1 Habitat protection
A formal provincial policy, preferably backedby regulation, is needed for protection of nestsites on Crown lands, particularly on thoselands designated for timber production. Thisshould specify that all nest trees be preserved,that a certain number of trees around them beretained for long-term replacement, and thatlogging adjacent to nest trees be done outsidethe nesting season. The number of trees orsize of patch to be left at any site requiresmore study, and may vary according to therelative availability of adjacent old growthleft uncut for other reasons. Many loggingoperators now attempt to protect known nesttrees, but some inconspicuous ones have in-advertently been cut. In some cases, only the
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nest tree has been left standing in a sea ofslash. Without replacement trees, future log-ging on an 80-year rotation will result in theloss of many nesting territories. Protection ofkey perching and roosting sites used in win-ter, as described for the Fraser Valley (Farrl988; Teske l989), probably needs to be ex-panded to other areas. Voluntary restraint bylogging companies may be sufficient to meetthis objective.
Protection of nest sites on private land is amore complex matter. On southeast Vancou-ver Island, most nest trees appear to be cut asa result of ignorance; therefore a public infor-mation program aimed at voluntary preserva-tion by land owners/managers is consideredto be the most urgent need (Blood l989b).Other mechanisms to preserve known nesttrees - easements, restrictive covenants, land-owner agreements, and administrative trans-fer of Crown parcels - may be appropriatewhere voluntary preservation is not promis-ing. Land purchase is too expensive to offeras a general approach, but should be consid-ered where sites have value as parkland.
Protection of key forage resources and habi-tats from degradation and pollution is alsoneeded. This is generally accommodated byexisting environmental legislation; however,more monitoring and enforcement is neededin some areas.
8.2.2 Eagle protection
Based on known causes of injury and deathrecorded for eagles in southwestern BritishColumbia, K. Langelier (pers. comm.) hasrecommended the following management/protection measures, in approximate order ofpriority:
l. Eliminate the use of lead shot forsport hunting.
2. Control or eliminate the use ofcarbofuran pesticides.
3. Move road-killed animals away fromroadsides to reduce eagle collisionmortality.
4. Investigate design of power lines andmodify this (e.g., greater spacing be-tween conductors) in areas whereelectrocution is a persistent problem.
5. Reduce or eliminate the use of leg-hold traps and snares by trappers.
6. Investigate predator control nets andcontrol methods at fish farms andmake appropriate modifications.
7. Intensify enforcement in areas whereshooting is a problem.
8. Publicize the need for careful dis-posal of the carcasses of livestockthat have been euthanized with bar-biturates.
Rehabilitation centres can play an importantrole in reducing eagle mortality, and suchefforts should be supported.
Protection from disturbance will probablybecome increasingly important in British Co-lumbia, particularly where large numbers ofeagles concentrate along salmon-spawningrivers in winter. Stalmaster (l983) recom-mended restricting land activities within 250m of eagles perched in shoreline trees, andsuggested that the distance could be short-ened to 75 to l00 m if dense shielding vegeta-tion was present. Knight and Knight (l984)found that restriction zones of 350 m wouldbe required in order to protect 99% of eaglesperched in shoreline trees from disturbanceby passing canoes along the Skagit andNooksack rivers. Where eagles are resting onriver bars, a zone of 450 m is needed to
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achieve the same level of protection. Restric-tion of boating activity during early morningand late afternoon feeding peaks has alsobeen recommended. These guidelines may beapplicable to British Columbia rivers if rec-reational boating becomes a problem in areaswhere wintering eagles are concentrated.
8.3 Research Needs
The following are perceived as the mostimportant research needs applicable to BaldEagle management and conservation in B.C.:
l. Assessment of forest practices in relationto nesting abundance
The major need is to determine how muchold growth is needed, either as scatteredindividual trees or as patches, and what itsspatial arrangement should be in order to re-tain nesting eagle populations that are as highas prior to logging. Evaluation of nestingactivity before, during, and after logging isneeded on a fairly large study area. The rela-tive importance for eagle nesting of oldgrowth left for other purposes, such as streamprotection, fire-breaks, or because it is notoperable or of poor commercial quality,should also be determined. Possibilities forsatisfying the needs of other old-growthnesters like Marbled Murrelets at the sametime as preserving eagle nest sites requirestudy.
2. Assessment of mortality rates
Information is needed on mortality rates inBritish Columbia and on the proportion ofthat mortality attributable to natural versushuman causes. Present programs in whichdead or injured eagles are submitted topathologists will continue to provide some
information of this kind; however, a compre-hensive long-term banding program isneeded. Biases resulting from the submissionof more eagles from settled areas wherehuman-related mortality is highest need to beevaluated.
3. Contaminants in eagles and their foods
Continued monitoring of prey items, and ofsick or dead eagles turned in to pathologylabs, is needed to determine whether knownproblems like lead poisoning are decreasing,or if any new contaminants are evident.
4. Movements
The degree to which the British ColumbiaBald Eagle population is shared with otherjurisdictions should be evaluated. The abovebanding program would shed light on this;however, marking with coloured vinyl tags isalso recommended, together with notificationof wildlife agencies in adjacent jurisdictionsof the program and the colour combinationsused. This would also aid in assessment ofthe movement of eagles between variousfood sources within the province.
5. Tolerance of human civilization
Monitoring of nesting populations in areaswhere human settlement and related landuses are expanding is needed to determinetolerance levels, and whether any decrease innesting abundance is due to loss of nest trees,loss of food resources and foraging sites, orsimply to increased levels of human activity.Eagles nesting in populated areas need to bestudied more thoroughly to determine howthey adapt to, and cope with, the trappings ofcivilization. Such studies would aid in pre-dicting impacts, such as cottage development
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around lakes, where only relatively low treeslike aspens are available for nesting.
6. Non-breeding by adults eagles
There is evidence that, in saturatedpopulations, over 50% of adult eagles maynot nest. Knowledge of the proportion that isnot breeding provides an index of the degreeto which the habitat in any area is saturated.The presence of few or no non-breeders mayindicate that a population is either decliningor has not reached carrying capacity. Sampleaerial surveys repeated every few years couldprovide this information.
9.0 EVALUATION
Concern for the world status of the BaldEagle (entirely confined to North America)has arisen because of gradual long-term habi-tat loss or alteration, shooting mortality priorto the l950s, and pesticide-induced declinesfrom the l950s to the l970s. The species hasrecovered from shooting losses, and appearsto be recovering from pesticide impacts.Habitat loss in the southern part of the spe-cies’ breeding range has probably reduced thecontinental population below that present l00or 200 years ago; however, historical censusdata are not available to confirm this. Atpresent, the bulk of the continental popula-tion occurs in Alaska, British Columbia, andacross the boreal forest of Canada. Thesepopulations are mostly stable, and the habitatis relatively secure, therefore the species as awhole does not appear to warrant Rare,Threatened, or Endangered status. Threat-ened or Endangered status has been assignedin jurisdictions where population size issmall, and/or has recently decreased due topesticide or other impacts. This includes On-tario, New Brunswick, and all of the lower 48states.
The Bald Eagle population in British Colum-bia is large (20,000-30,000), and apparentlystable or increasing in most regions. Designa-tion of the provincial population as Rare,Threatened, or Endangered does not appearwarranted. The species is currently on theMOELP Wildlife Program’s Blue List, whichincludes taxa that are considered vulnerableor sensitive. Species may also be on this listbecause of an inadequate understanding oftheir status.
The Bald Eagle is sensitive to extensive lossof nest trees, but will continue to nest whereonly scattered veteran trees remain. It is rela-tively tolerant of non-threatening human ac-tivity, will nest in suburban environments,and has adapted to many food sources madeavailable by humans. Although eagles requiretrees for nesting, they forage largely inaquatic habitats, and these are mostly secure.They appear to be less threatened than manyother species that require old-growth forestfor both nesting and foraging. On a provin-cial basis, the Bald Eagle does not appear todeserve Blue List status. In view of the highprofile of this species and its potential impor-tance for nature-based tourism, inclusion onthe provincial Yellow List appears to be desir-able.
If Red, Blue, and Yellow List criteria wereapplied on a regional basis, then the Bald Ea-gle might warrant Blue List status in theGeorgia Depression Ecoprovince. Its longterm prospects here would seem to approxi-mate those of adjacent Washington State,where it has been designated as Threatened.
In the absence of management action, agradual decline in nesting populations couldbe expected in localized areas subject to ex-tensive clear-cutting or land settlement. How-ever, programs aimed at identification and
64
preservation of existing nest trees, plus addi-tional replacement trees, could arrest such de-clines. More effort is needed to achieve thisobjective.
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, S.G. Sealy, M. Lemon, and M.Rodway. l984. Predation and potentialenvironmental perturbances on AncientMurrelets nesting in British Columbia.Pages 757-770 in ICBP Tech. Publ.No. 2.
, K.R. Summers, and D.S. Bingham.l976. Birds observed at Triangle Island,British Columbia, l974 and l975. TheMurrelet 57(2):35-42.
Waste, S.M. l982. Winter ecology of the baldeagles of the Chilkat Valley, Alaska. InD.M. and P.F. Schempf, eds. 1982. Pro-ceedings of a symposium and workshopon raptor management and biology inAlaska and western Canada. U.S. Fishand Wildl. Serv., Anchorage, Alas.
Wright, B.S. l953. The relation of bald eaglesto breeding ducks in New Brunswick. J.Wildl. Manage. 17(1):55-62.
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11.0 ACKNOWLEDGEMENTS
The lead agency in the production of this re-port was the British Columbia Ministry ofEnvironment, Lands and Parks, WildlifeBranch. The report was authored by D.A.Blood and G.G. Anweiler, under the directionof W.T. Munro. This project was coordinatedby Myke Chutter, Bird Specialist
The following individuals provided unpub-lished information or advice: Jack Barrett,Denise Brownlie, Wayne Campbell, BillDumont, David Dunbar, Gary Kaiser, TrevorKinley, Ken Langelier, Alan McLeod, MikeMcNall, Rosamund Pojar, Allen Poynter,Anne Rahme, Jim Shaver, Chris Siddle andPeter Van Kerkoerle.
Maggie Paquet was responsible for theEnglish edit, and Gail Harcombe producedthe final figures, design, layout, and final editof the document.
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75
Appendix 1. Reproductive terminology1
Breeding area - An area containing one or more nests within the range of one mated pair ofeagles.
Occupied nest - A nest at which a mated pair of adult eagles is present, has repaired the nest,and/or has laid eggs as evidenced by an adult in incubating or broodingposture, observed eggs, or young.
Active nest - An occupied nest in which eggs are laid, as determined by observing anadult eagle in brooding or incubating posture, or observing eggs or young.
Successful nest - A nest in which at least one nestling is raised to fledging or near-fledgingage.
Brood size - The number of young at fledging or near-fledging age per successful nest.
Productivity - The number of young at fledging age per occupied or active nest, asindicated.
Alternate nest - An unoccupied nest within the breeding area of a pair of eagles.
1 Based on Postupalsky 1974 and Swenson et al. 1986.
76
Appendix 2. The number of Bald Eagles counted on Christmas Bird Counts in BritishColumbia, December 1973 through December 1988.1
Location Total Counts % Counts No. Bald Eagles SeenDone Eagles Seen Range x/count
COASTAL
Marine Shorelines
Bamfield 3 100 25 - 68 46 Bella Bella 1 100 - 19 Campbell River 12 100 9 - 160 54 Comox 16 100 20 - 191 100 Deep Bay 14 100 67 - 424 252 Duncan 16 100 11 - 249 70 Hecate Strait 1 100 - 9 Kitimat 11 100 2 - 56 19 Ladner 16 100 3 - 96 34 Massett 6 100 9 - 52 32 Nanaimo 16 100 32 - 241 77 Pender Island 16 100 11 - 117 48 Port Alberni 1 100 - 19 Port Clements 5 100 1 - 20 9 Prince Rupert 9 100 8 - 60 35 Rose Spit 3 100 8 - 13 10 Sayward 12 100 3 - 25 12 Skidegate Inlet 7 100 37 - 65 8 Sooke 6 100 11 - 50 28 Squamish 9 100 131 - 1,398 732 Sunshine Coast 9 100 14 - 71 30 Vancouver 16 100 7 - 88 31 Victoria 16 100 9 - 48 27 White Rock 14 100 1 - 32 10
Non-Marine
Chilliwack 13 100 5 - 134 37 Pitt Meadows 15 100 7 - 77 24 Terrace 16 100 1 - 58 18
77
Appendix 2. (Continued).1
Location Total Counts % Counts No. Bald Eagles SeenDone Eagles Seen Range x/count
INTERIOR
Okanagan/Shushwap
Kamloops 5 60 0 - 7 3 Kelowna 4 100 2 - 12 6 Oliver/Osoyoos 10 100 1 - 9 4 Penticton 13 100 1 - 15 5 Salmon Arm 1 100 - 6 Shushwap Lake Park 16 94 0 - 27 9 Vaseux Lake 15 93 0 - 7 4 Vernon 14 100 3 - 13 7
Kootenay/Columbia
Cranbrook 5 60 0 - 2 1 Creston 2 100 2 2 Fauquier 5 100 1 - 3 2 Lake Windermere 6 100 2 - 7 5 Nakusp 10 60 0 - 1 1 Nelson 1 100 - 2 Revelstoke 8 63 0 - 3 1 Yoho National Park 5 20 0 - ? <1
Central and Northern
Fort St. James 2 100 3 3 Fort St. John 4 0 - 0 Mackenzie 1 0 - 0 North Pine 6 0 - 0 Quesnel 4 75 0 - 1 <1 Smithers 12 92 0 - 10 4 Wells Gray Park 2 0 - 0
1 Source: American Birds
Wildlife Working Reports should not be cited because of the preliminary nature of the data they contain. Working Reports 1 - 10 are out ofprint.
WR-11 Effect of wolf control on black-tailed deer in the Nimpkish Valley on Vancouver Island. Progress report -1983 August 31 to 1984August 31. K. Atkinson and D. Janz. March 1985. 22pp.
WR-12 1983 southeastern Skeena regional moose abundance and composition survey. B. van Drimmelen. June 1985. 47pp.
WR-13 Kechika Enhancement Project of northeastern B.C.: wolf/ungulate management. 1984-85 annual report. J.P. Elliott. September1985. 28pp.
WR-14 Muskwa Wolf Management Project of northeastern B.C. 1984-85 annual report. J.P. Elliott. September 1985. 44pp.
WR-15 Caribou habitat use on the Level Mountain and Horseranch ranges, British Columbia. M.A. Fenger, D.S. Eastman, C.J. Clement,and R.E. Page. 1986. 41pp + 4 maps. (Also printed as Surveys and Resource Mapping Branch Working Report WR-8).
WR-16 Working plan - coastal grizzly research project. W.R. Archibald and A.N. Hamilton. October 1985. 27pp. (Also printed as WHR-21).
WR-17 Progress report - year 3 - 1984, working plan - year 4 - 1985. Coastal grizzly research project. W.R. Archibald, A.N. Hamilton,and E. Lofroth. October 1985. 65pp. (Also printed as WHR-22).
WR-18 Morice biophysical study, 93L/SW. B. Fuhr, M. Fenger, L. Lacelle, R. Marsh, and M. Rafiq. March 1986. 63pp + 9 maps.
WR-19 Effect of wolf control on black-tailed deer in the Nimpkish Valley on Vancouver Island. Progress report - 1984 August 31 to 1985August 31. K. Atkinson and D.W. Janz. March 1986. 27pp.
WR-20 Kechika Enhancement Project of northeastern B.C.: wolf/ungulate management. 1985-86 annual report. J.P. Elliott. December1986. 17pp.
WR-21 Muskwa Wolf Management Project of northeastern B.C. 1985-86 annual report. J.P. Elliott. December 1986. 15pp.
WR-22 Progress report - year 4 - 1985, working plan - year 5 - 1986. Coastal grizzly research project. A.N. Hamilton, W.R. Archibald,and E. Lofroth. November 1986. 100pp. (Also printed as WHR-26).
WR-23 Critical habitat of caribou (Rangifer tarandus caribou) in the mountains of southern British Columbia. K. Simpson, K. Hebert, andG.P. Woods. February 1987. 13pp.
WR-24 Impacts of a hydro-electric reservoir on populations of caribou and grizzly bear in southern British Columbia. K. Simpson. February1987. 40pp.
WR-25 The effects of snowmobiling on winter range use by mountain caribou. K. Simpson. February 1987. 15pp.
WR-26 Quesnel Highlands wolf control project. D. Hebert. January 1987. 10pp.
WR-27 Muskwa Wolf Management Project of northeastern B.C. 1986-87 annual report. J.P. Elliott. April 1987. 20pp.
WR-28 Vancouver Island wolf control project. Year 1 progress report. D. Janz. July 1987. 11pp.
WR-29 Habitat survey of the Mackenzie Heritage Trail corridor. V. Hignett. June 1987. 21pp + 5 maps.
WR-30 A proposal to manage coyote and cougar populations of the Junction Wildlife Management Area. D. Hebert. September 1987.11pp.
WR-31 Wildlife habitat suitability of the Mackenzie Heritage Trail corridor. V. Hignett. May 1988. 16pp + 6 maps.
WR-32 Research priorities for furbearers in British Columbia. D. Blood. June 1988. 49pp.
WR-33 Electrically triggered drop net to capture wild sheep. J.W. Hirsch. January 1988. 18pp.
WR-34 A lynx management strategy for British Columbia. D.F. Hatler. July 1988. 121pp.
WR-35 Causes of bighorn sheep mortality and dieoffs - literature review. H.M. Schwantje. April 1988. 54pp.
WR-36 Explanatory legend for vegetation maps of the Kamloops Lake bio-physical study area. E.C. Lea. December 1988. 78pp.
Continued from inside back cover
WR-37 Bio-physical habitat units and interpretations for moose use of the upper Cariboo River Wildlife Management Area. E.C. Lea, T.Vold, J. Young, M. Beets, D. Blower, J. Youds, A. Roberts. December 1988. 24pp.
WR-38 Grizzly bear habitat of the Flathead River area: expanded legend. E.C. Lea, B.L. Fuhr, and L.E.H. Lacelle. December 1988. 24pp.
WR-39 Managing habitat through guidelines: How far can you go? M. Fenger and V. Stevens, eds. February 1989. 48pp.
WR-40 Wolf-prey dynamics. Proceedings of a symposium sponsored by B.C. Ministry of Environment, Wildlife Branch, Faculty of Forestry,University of British Columbia and the Northwest Wildlife Preservation Society. February 1989. 188pp.
WR-41 Caribou research and management in B.C.: proceedings of a workshop. R.Page, ed. November 1988. 275pp. (Also printed asWHR-27)
WR-42 Trapping in British Columbia - a survey. R. Reid. January 1989. 55pp.
WR-43 Biophysical habitat units of the Lower Halfway study area: expanded legend. E.C. Lea and L.E.H. Lacelle. December 1989. 33pp.
WR-44 Long range habitat planning: proceedings. M. Fenger and V. Stevens, eds. March 1990. 49pp.
WR-45 Biophysical habitat units of the Mosley Creek study area: expanded legend and interpretations. E.C. Lea and R.C. Kowall. March1990. 33pp.
WR-46 Habitat Management Section. Annual General Meeting. Yellowpoint Lodge - 1989 April 25-27. Wildlife and Recreational FisheriesBranches, Ministry of Environment. July 1990. 107pp.
WR-47 Working plan — Khutzeymateen Valley grizzly bear study. A.N. Hamilton and J.A. Nagy. September 1990. 35pp. (Also printed asWHR-28).
WR-48 Khutzeymateen Valley grizzly bear study. Annual progress report - year 1 (1989/90), annual working plan - year 2 (1990/91). J.A.Nagy and A.G. MacHutchon. January 1991. 44pp. (Also printed as WHR-29).
WR-49 Fort Nelson and area average winter maximum snowpack mapping. R. Chilton. July 1990. 12pp.
WR-50 Marten habitat suitability research project - working plan. E.C. Lofroth and V. Banci. January 1991. 31pp.
WR-51 Khutzeymateen Valley grizzly bear study. Annual progress report - year 2 (1990/91), annual working plan - year 3 (1991/92). A.G.MacHutchon and S. Himmer. March 1992. 36pp. (Also printed as WHR-30)
WR-52 Abundance, Distribution and Conservation of Birds in the Vicinity of Boundary Bay, B.C. R.W. Butler, ed. 1992. 132pp. (Alsoprintes as Technical Report Series No. 155, Pacific and Yukon Region, Can. Wildlife Service).
WR-53 Status of the Clouded Salamander in British Columbia. T.M. Davis and P.T. Gregory. March 1993. 19pp.
WR-54 Status of the Northern Pacific Rattlesnake in British Columbia. M.B. Charland, K.J. Nelson, P.T. Gregory. March 1993. 23 pp.
WR-55 Status of the Shrew-mole in British Columbia. L. Kremsater, L. Andrusiak, F.L. Bunnell. March 1993. 26 pp.
WR-56 Status of the Nuttall’s Cottontail in British Columbia. D.W. Carter, A. Harestad, F.L. Bunnell. March 1993. 33 pp.
WR-57 Status of the Sharp-tailed Snake in British Columbia. D.J. Spalding. March 1993. 15pp.
WR-58 Guidelines for Technical Publications of the Wildlife Program. E. Stanlake. March 1993. 57pp.
WR-59 Status of Keen's Long-eared Myotis in British Columbia. M. Firman, M. Getty, and R.M.B. Barclay. March 1993. 29pp.
WR-60 Biophysical Habitat Units for the Tatlayoko Lake Study Area: expanded legend and interpretations. E.C. Lea and R.C. Kowall.March 1993. 22pp.
WR-61 Status of the Pallid Bat in British Columbia. K. Chapman, K. Mc Guinness, R.M. Brigham. February 1994. 32pp.
WR-62 Status of the Bald Eagle in British Columbia. D.A. Blood and G. G. Anweiler. February 1994. 92pp