FACTORS INFLUENCING BIRD POPULATIONS

IN SOUTHWESTERN RIPARIAN FORESTS

Robert C. Szaro

Wildlife Biologist USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Tempe, Arizona 85281

ABSTRACT

Riparian forests comprise only a minor portion of the avail­able habitat in the arid Southwest, but support extremely high bird populations. Most birds show a remarkable dependency on water related habitat for breeding areas, wintering areas, and migratory corridors. Bird communities in riparian forests are affected by vegetation type, structure, density, temporal fluctuations, adjacent habitat, recreational use, grazing, and location.

KEYWORDS: riparian forest, bird populations, vegetation type.

Riparian bird populations in the Southwest are affected by a multitude of complex and interacting factors. Riparian habitats range from low desert to high alpine meadows (Pase and Layser 1977). Bird densities, species numbers, and diversity vary with changes in vegetation type, structure, density, temporal fluctuations, adjacent habitat, recreational use,· grazing and location (Aitchison 1977, Anderson and Ohmart 1977a and b, Carothers et al. 1974, Stevens et al. 1977).

Riparian habitats are comparatively rare (e.g., less than 1/2 percent of the land area in Arizona), but the breeding avifauna of the Southwest lowlands shows a remark­able dependency on these water related habitats (Johnson et al. 1977). Of 166 breed­ing species examined from southern Arizona, southern New Mexico, and west Texas, 77 percent were in some manner dependent on these areas and 51 percent are completely dependent on this habitat (Johnson et al. 1977). Carothers and Johnson (1975) found that over 50 percent of the species breeding in homogeneous Fremont cottonwood stands along the Verde River, Arizona, are exclusively dependent on this habitat for repro­duction. Their studies showed no other habitat in North America as important to non­colonial nesting birds.

Riparian areas are important not only to breeding bird populations but to winter residents and migrants as well. Riparian habitats act as concentrators of birds

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This file was created by scanning the printed publication.Errors identified by the software have been corrected;

however, some errors may remain.

(Goldberg et al.l/, Stevens et al. 1977). The value of a given riparian habitat varies from species to species and seasonally for the same species (Anderson and Ohmart 1976).

This paper examines many of the factors influencing riparian bird populations in the Southwest and offers some management recommendations. The discussion follows Lowe's (1964) definition of a riparian association as "in or adjacent to drainageways and/or their floodplains and which is further characterized by species and/or life forms different from that of the immediately surrounding non-riparian climax." This includes vegetation along both perennial and ephemeral stream courses. The area under consideration ranges from western Texas through New Mexico and Arizona to southern California, and includes the southern portions of Nevada, Utah, and Colorado.

VEGETATION

Southwestern riparian habitats include a diverse mixture of trees and shrubs (Hubbard 1977). Communities at the lower elevations consist primarily of mesquite (Prosopis juliflora) and saltcedar (Tamarix chinensis) changing through a continuum of vegetative associations to high elevation woodlands of alder (Alnus spp.) and willow (Salix spp.) (Pase and Layser 1977). Perhaps because of the relatively small amount of riparian habitat in the Southwest and its extreme complexity,little information is available on the range of vegetative types found in this region.

Although there is no site-based classification system for riparian vegetation, Brown et al. (1979) have developed a digitized nomenclature for southwestern wetland biotic communities. This system indicates the potential array of riparian associa­tions in the region (Table 1). Their listing of communities is tentative, and will be modified as more data become available. Yet with only the beginnings of a classi­fication it becomes clear that managing riparian habitats for nongame bird populations will ultimately depend on bird community information from each association.

1/ -Goldberg, Nancy H., N. Joseph Sharber, Laurence E. Stevens and Steven W. Carothers. 1979. Distribution and abundance of nongame birds in riparian vegetation in Arizona. Museum of Northern Arizona, Flagstaff, Arizona and Rocky Mt. For. and Range Exp. Stn., Tempe, Ariz. Unpublished manuscript.

TABLE 1.--Tentative classification of riparian forest and scrub associations in the Southwest (modified from Brown et al. 1979).

Nearctic Wetland Vegetation Forest Formation

Cold Temperate Swamp and Riparian Forests Plains and Great Basin Riparian Deciduous Forest

Cottonwood-Willow Series 1. Populus sargenti Association 2. Populus sargenti-Salix amygdaloides Association 3. Populus wislizenii Association 4. Populus spp.-Salix spp. Association 5. Salix exigua Association

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TABLE 1. (cont' d.)

Rocky Mountain Riparian Deciduous Forest Cottonwood-Willow Series

6. Populus angustifolia-Salix spp. Association 7. Populus angustifolia Association

Mixed Broadleaf Series 8. Acer negundo-Populus angustifolia-mixed

deciduous Association 9. ~ulus angustifolia-mixed deciduous

Association 10. Acer negundo Association 11. Acer glabrum Association 12. Acer grandidentatum Association

Warm Temperate Swamp and Riparian Forests Interior Southwestern Riparian Deciduous Forest and Woodland

Cottonwood-Willow Series 13. Populus fremontii-Salix spp. Association 14. Populus fremontii Association 15. ~opulus fremontii-mixed deciduous Association 16. Populus wislizenii Association 17. Populus acuminata Association

Mixed Broadleaf Series 18. Platanus wrightii-Fraxinus velutina-Populus

fremondi-mixed deciduous Association 19. Platanus wrightii-Quercu.s spp.-Juniperus

spp. Association 20. Plantanus wrightii Association 21. Fraxinus velutina Association 22. Alnus oblongifolia Association 23. Juglans major Association

Californian Riparian Deciduous Forest and Woodland Cottonwood-Willow Series

24. Populus fremon~Salix spp. Association 25. Salix spp.-Populus fremontii Association 26. Platanus racemosa-mixed deciduous Association 27. Platanus racemosa-Quercus agrifolia Association 28. Alnus rhombifolia Association

Tropical-Subtropical Swamp, Riparian and Oasis Forests Sonoran Riparian and Oasis Forests

Palm Series 29. Washingtonia filifera Association 30. Washingtonia filifera-Populus fremonti Association

Mesquite Series 31. Prosopis juliflora Association 32. Prosopis juliflora-mixed short tree Association 33. Prosopis pubescens Association

Cottonwood-Willow Series 34. Populus fremon~-Salix gooddingi Association 35. Populus fremontii A::Eociation 36. Salix gooddingi Association 37. Salix bonplandiana Association 38. Salix spp.-mixed deciduous Association

Swampscrub Formation Arctic-Boreal Swampscrubs

Rocky Mountain Alpine and Subalpine Swamp and Riparian Scrub Willow Series

39. Salix bebbiana Association 40. Salix spp.-Alnus spp. Association 41. Salix spp. Association

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j. 1_,.

l

TABLE 1. Alder Series (cont'd.) 42. Alnus tenuifolia Association

43. Alnus tenuifolia-Salix spp. Association Cold Temperate Swamp and Riparian Scrubs

Plains and Great Basin Swamp and Riparian Scrub Willow Series

44. Salix spp.-mixed scrub Assocation Saltcedar Disclimax Series

45. Tamarix chinensis Association Rocky Mountain Riparian Scrub

Willow-Dogwood Series 46. Salix spp.-mixed deciduous Association

Willow Series 47. Salix spp. Association

Warm Temperate Swamp and Riparian Scrubs Interior Southwestern Swamp and Riparian Scrub

Mixed Narrowleaf Series 48. Cephalanthus Occidentalis-Baccharis glutinosa­

mixed scrub Association Saltcedar Disclimax Series

49. Tamarix chinensis-mixed deciduous Association Californian Deciduous Swamp and Riparian Scrub

Mixed Narrowleaf Series SO. Salix lasiolepis Association 51. Salix spp. Association

Tropical-Subtropical Swamp and Riparian Scrub Sonoran Deciduous Swamp and Riparian Scrub

Mixed Scrub Series 52. Prosopis pubescerurProsopis juliflora torreyana­

Pluchea sericea Association Saltcedar Disclimax Series

53. Tamarix chinensis Association 54. Tamarix chinensis-mixed scrub Association

Bird community structure is known only from a fraction of these associations and in many of them where data are available, the information is from only a single location and year ~able 2). Breeding bird densities in riparian communities are dependent on vegetation type and generally are much higher in it than in the surround­ing habitat (Anderson and Ohmart 1977a, Goldberg et al. 1979). Reported densities range from a high of 1059 pairs/40 ha in a cottonwood area in central Arizona (Carothers and Johnson 1975) to a low of 11 pairs/40 ha in a mesquite area in Nevada (Austin 1970) and a saltcedar area in California (Weinstein and Berry 1978).

Even within the same vegetative association, breeding bird densities, diversity and species richness differ from location to location. For example, density in five Fremont cottonwood plots varied from 425 to 847 pairs/40 ha, species richness from 20 to 28, and diversity from 2.68 to 3.15 (Table 2). Similar differences are found in willow, mesquite, and saltcedar habitats.

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TABLE 2.--Breeding bird community parameters: species richness (SR), bird species diversity (BSD) and density (DEN) of selected riparian forests in the Southwest.

Association SR BSD DEN2

Plains cottonwood (1)1

25 Plains cottonwood (1) 20 Cottonwood-willow-pine (6) 33 Cottonwood-willow (13) 27 Fremont cottonwood (14) 26 Fremont cottonwood (14) 22 Fremont cottonwood (14) 20 Fremont cottonwood (14) 22 Fremont cottonwood (14) 28 Cottonwood-ash (15) 13 Cottonwood-ash-willow (15) 19 Mixed deciduous (18) 17 Mixed deciduous (18) 19 Mixed deciduous (18) 22 Mixed deciduous (18) 21 Sycamore-live oak-juniper (19) 36 Ash-walnut-willow (21) 20 Ash-mesquite-hackberry (21) 19 Alder-ash-sycamore (22) 10 Walnut-mesquite-sycamore (23) 24 Cottonwood-willow (24) 32 Cottonwood-willow (24) 21 Cottonwood-willow-mesquite(24) 37 Willow-cottonwood (25) 20 Willow-cottonwood (25) 20 Sycamore-coast live oak (27) 21 Sycamore-coast live oak (27) 32 Sycamore-coast live oak (27) 22 Palm oasis (29) 5 Mesquite (31) 31 Mesquite (31) 13 Mesquite (31) 12 Mesquite (31) 19 Mesquite (31) 14 Mesquite-willow (32) 21 Mesquite-saltcedar (32) 10 Bebb's willow (39) 7 Willow (41) 4 Saltcedar-saltbush (49) 5 Saltcedar-marsh (49) 23 Arroyo willow (50) 13 Willow-mesquite (51) 8 Saltcedar (54) 28

2.30 748 2.08 137 3.02 348 2.67 354 2.98 847 2.53 512 2.68 425 2.71 612 3.15 684 2.46 639 2.42 510 2.78 193 2.61 332 2.85 312 2.87 359 3.29 609 2.16 352 2.70 310 2.17 326 2.90 503 3.55 456 2.92 394 3.15 197 2.76 197 2.38 740 2.77 348 3.09 607 2.84 258 1. 33 97 2.74 190 2.35 11 2.33 49 2.60 244 2. 04 151 2.33 186 1.47 167 1. 89 286 1.47 826 1. 33 11 2.32 43 2.21 597 1. 62 520 2.16 243

;Numbers in parentheses refer to Table 1 Pairs per 40 hectares

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State

co co NM TX AZ AZ AZ AZ AZ AZ AZ AZ AZ AZ AZ AZ AZ AZ AZ AZ CA CA CA CA CA CA CA CA CA AZ NV NV AZ CA CA CA AZ AZ CA CA CA CA TX

Source

Justice et al. 1979 Hanka 1979 McCallum 1979 Engel-Wilson & Ohmart 1978 Carothers et al. 1974 Carothers et al. 1974 Carothers et al. 1974 Carothers et al. 1974 Stamp 1978 Goldberg et al. 1979 Goldberg et al. 1979 Carothers et al. 1974 Carothers et al. 1974 Carothers et al. 1974 Goldberg et al. 1979 Barker 1979 Goldberg et al. 1979 Goldberg et al. 1979 Goldberg et al. 1979 Goldberg et al. 1979 Manolis 1973 Gaines 1973 Goldwasser 1978 Ingles 1950 Woodman 1978 Gundy & Flanagan 1978 Loveless & Loveless 1978 McKinnie 1974 Koopman 1979 Anderson & Ohmart 1977a Austin 1970 Austin 1970 Stamp 1978 Evens 1979a Evens 1979b Jehl 1978 Goldberg et al. 1979 Goldberg et al. 1979 Weinstein & Berry 1978 Cardiff et al. 1978 Atwood 1978 McKernan 1978 Engel-Wilson & Ohmart 1978

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VEGETATION STRUCTURE AND DENSITY

Bird community differences within vegetative associations partially reflect differences in vegetation structure and density. Carothers and Johnson (1975) found a direct correlation between breeding bird density and tree density in cotton­wood areas of central Arizona (Table 3).

TABLE 3.--Average breeding bird densities found on manipulated vs. unmanipulated homogenoous Fremont cottonwood study plots (Carothers and Johnson 1975).

Study plot Trees/Hectare Bird Density (Prs/40 ha)

Control 113 1059

Area 2 63 758

Area 3 25 484

They suggest that population densities decline even more rapidly when tree density falls below 25 trees/hectare. Vegetation structure, that is the proportion of foliage present in horizontal strata above the ground, indicates resource distri­bution in the habitat and thereby affects bird populations (Szaro and Balda 1979). Al0ng the lower Colorado River, foliage density in height intervals of 0.15-0.6 m, 0.6- 1.5 m, 1.5- 3.0 m, 3.0- 4.6andgreater than 4.6 m was used in computing a matrix of overlap values. From these values a dendrogram was constructed showing study sites with greatest affinities between foliage density and structure. This analysis indicated six distinct structural types in cottonwood-willow, mesquite, and saltcedar communities along the Colorado (Anderson et al. 1977a). In the six structural types of saltcedar communities, bird density, diversity, and species richness varied from 131 to 503 birds/40 ha, 1.85 to 2.53, and 18 to 25 species. respectively (Table 4) (Anderson et al. 1977b).

TABLE 4.--Densities, diversities and species richness in six saltcedar structural types, lower Colorado River Valley, May through July (Anderson et al. 1977b).

Structural type 1 Species Richness Diversity Density (Birds/40 ha)

I 25 2.50 290 II 20 2.04 503

III 19 1.85 316 IV 18 1.93 241 v 20 2.44 131

VI 24 2.53 226

1structural types differentiated by foliage distribution with foliage volume shifting

from a predominance at greater than 9.0 m in type I to a predominance at less than 3.0 min type VI (See Anderson et al. 1977a for a complete description).

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YEARLY AND SEASONAL FLUCTUATIONS

Bird community organization is known to fluctuate yearly (Szaro and Balda 1979), and seasonally (Fretwell 1972) in a wide variety of habitat types including riparian types (Anderson and Ohmart 1977a). Community organization during the spring breeding season may reflect resource-based interspecific competition, while wintering assem­blages of birds are probably regulated by harsh and variable climate (Rotenberry et al. 1979). Species diversity, richness, and diversities in riparian plant communities typically show summer maxima and winter minima (Tables 5 and 6)(Anderson and Ohmart 1977a, Rotenberry et al. 1979). Community structure also fluctuates from year to year, probably reflecting climatic events during the nonbreeding season (Fretwell 1972). For example, in a plains cottonwood community over a 7-year period, breeding bird density ranged from 544 to 748 pairs/40 ha, species richness from 23 to.29 species, and diversity from 2.30 to 2.86 (Table 7). Similar fluctuations have been observed in cottonwood-willow, mesquite, and saltcedar along the lower Colorado River (Table 5) (Anderson and Ohmart 1976).

Habitat requirements shift seasonally with changes in community organization because winter requirements of birds are different from breeding requirements (Anderson and Ohmart 1977a). Correlations between population parameters and vegetation structure varied seasonally in the lower Colorado, with habitat breadth being narrowest in winter and broadest in summer. Most species showed some consistency in habitat preference between seasons but only a minority of species showed close associations (Anderson and Ohmart 1977a). Models that predict a high degree of habitat consistency over an entire year must be used with care because many species may not fit the pattern (Anderson and Ohmart 1977a).

Bird community composition changes from season to season as winter and summer residents come and go. Anderson and Ohmart (1976) indicate that ruby-crowned king­lets (Regulus calendula), white-crowned sparrows (Zonotrichia leucophrys), and yellow-rumped warblers (Dendroica coronata) are prevalent members of winter bird assemblages in cottonwood-willow areas along the lower Colorado. However the same species are absent during the breeding season (Table 8). Conversely, ash-throated flycatchers (Myiarchus cinerascens), verdins (Auriparus flaviceps) and brown-headed cowbirds (Molothrus ater) are important summer breeders but of minor importance or entirely absent during the winter. Permanent resident species such as mourning doves (Zenaida macroura), Abert's towhees (Pipilo aberti), and Gambel's quail (Lophortyx gambelii), are major components in all seasons but greatly increase in density during the spring, summer, and late summer periods. Other permanent resi­dents such as the black-tailed gnatcatcher (Polioptila melanuta) maintain relatively stable populations throughout the year.

Additional variation during the spring and fall is due to the value of riparian areas as migratory corridors (Rappole and Warner 1976, Stevens et al. 1977, Wauer 1977). Species preferences for riparian areas are shown by differing migrant den­sities and species diversities in various habitats (Stevens et al. 1977).

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TABLE 5.--Seasonal and yearly flux in density and species richness in four vegetation types along the lower Colorado River Valley (Anderson and Ohmart 1976).

Year

1975 1976

1975 1976

1975 1976

1975 1976

Bird density per 40 hectares by season (species richness)

Winter 1 Spring Summer Late Summer Fall

119(13) 149(34)

195 (19) 258(23)

28 (11) 24 (12)

58(13) 40 (15)

Cottonwood-Willow

128(29) 194(37)

260(20) 341(31)

Honey-Mesquite

176(28) 192(28)

239(19) 354(20)

Saltcedar

105(17) 49(12)

126(19) 237(16)

Saltcedar-Honey Mesquite

68 (19) 115(21)

137(19) 292(19)

273(20) 296(35)

164(20) 208(25)

85(12) 188(22)

213(19) 181(19)

157 (16) 166(31)

261(24) 163(25)

76 (14) 106(21)

137(22) 176(21)

1Winter =December, January, February; Spring = March and April; Summer =May,

June, and July; Late Summer =August and September; Fall = October and November

TABLE 6.--Seasonal changes in bird community structure in a mesquite bosque (Gavin and Sowls 1975).

Density Species Additional Bird Bird Species Month and Year (Birds/40 ha) Richness Species Recorded Diversity

January 1972 104.4 4 11 1.24 February 112.2 4 19 1.18 March 290.8 11 17 2.11 April 539.4 12 19 1. 78 May 412.5 11 20 1. 90 June 370.8 10 20 1. 91 July 241.6 13 17 1.63 August 146.8 8 19 1. 78 September 98.0 5 27 1.43 October 77.6 4 17 1.19 November 48.4 4 14 1.20 December 20.2 2 14 0.68 January 1973 45.0 4 15 1.08 February 85.4 4 19 1.13 March 116.0 3 16 1.05 April 360.5 9 29 1.57

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TABLE 7.--Yearly fluctuations in breeding bird density, species richnes~ and diversity in a Plains Cottonwood community, Jefferson County, Colorado.

Year

1978 1977 1976 1975 1974 1973 1972 1971

X

Density (Prs/40 ha)

748 544 581 579 633 571 604 683

618

Species Richness

25 29 25 23 24 25 25 24

25

Bird Species Diversity

2.30 2.70 2.55 2.78 2.86 2.71 2:72 2.86

2.69

1compiled from Botorff et al. 1973, 1974; Hurley et al. 1971, 1975, 1977; Justice et al. 1978, 1979; Kingery and Botorff 1972.

TABLE 8.--Seasonal flux in bird densities (Birds/40 ha) for 10 species in cottonwood­willow habitats along the lower Colorado River (Anderson and Ohmart 1976).

Season Species Winter Spring Summer Late Summer Autumn

Ruby-crowned kinglet 12.0 3.5 0 0 18.5 White-crowned sparrow 12.0 1.0 0 4.0 13.5 Mourning dove 18.5 25.0 86.5 48.5 27.0 Abert's towhee 5.5 11.5 25.5 24.0 14.0 Verdin 3.0 8.5 11.5 12.5 12.0 Ash-throated flycatcher 0.5 8.0 12.0 8.0 1.0 Yellow-rumped warbler 32.5 19.0 1.0 0.5 31.0 Brown-headed cowbird 0 11.0 22.5 2.0 0 Black-tailed gnatcatcher 6.0 4.5 4.0 3.5 3.0 Gambel's quail 1.5 9.0 24.0 20.5 4.0

ADJACENT HABITATS

Areas adjacent to riparian habitats play a major role in determining the compo­sition of riparian bird communities (Stevens et al. 1977). In their study, riparian plots in central Arizona contained up to 10.6 times the number of migrants per hectare as adjacent nonriparian plots. Adjacent habitats that were of low value to birds promoted a higher concentration of migrants in riparian habitats.

Breeding bird communities in riparian habitats are typically more diverse and with higher densities than their adjacent nonriparian areas (Table 9). However, there is considerable use of adjacent habitats by riparian birds (Goldberg et al. 1979). Pleasants (unpublished manuscript, as cited in Goldberg et al. 1979) studying foraging behavior in northern orioles breeding in sycamore and cottonwood habitats

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bounded by sage and chaparral type vegetation, found that the orioles spent 19 to 84% of their time foraging in adjacent habitats. Of the number of breeding bird species reported from the four riparian sites in Table 9, 16 out of 19 (84%), 9 out of 22(41%), 13 out of 24 (54%), and 11 out of 21 (52%) were censused regularly in the adjacent habitats.

The relative productivity of areas adjacent to riparian habitats may account for part of the difference between the bird communities on mixed deciduous and cottonwood areas (Carothers et al. 1974, Goldberg et al. 1979). Birds breeding in the cotton­wood areas spend a greater proportion of their time foraging outside the nesting habitat than did breeding birds in mixed deciduous types. The cottonwood areas studied were adjacent to agricultural or second growth fields;and pastures that are highly productive in terms of insect biomass but not in breeding birds. Mixed decid­uous woodlands are bounded by mesquite bosques, pinyon-juniper-oak, chaparral and desert scrub-grassland. Insect biomass is lower in these areas than in cultivated fields; each area is inhabited by its own complement of nesting species (Carothers et al. 1974). Thus breeding bird density is higher in the cottonwood sites probably because of(l) an increased food supply and 0) lack of intra- and interspecific competition in the adjacent agricultural areas.

Agricultural use of riparian areas and adjacent habitats is commonplace in the Southwest. Agriculture and the clearing of the riparian strip reduced the total number of birds per hectare per year near Knights Landing, California from 1566 to 106. In contrast there were 2262 birds/hectare-year in combination riparian and agriculture areas (Hehnke and Stone 1978). Agricultural encroachment typically increases seasonal densities of riparian species in the agricultural riparian edge; however 22 riparian species were lost with agricultural encroachment of riparian habitats along the lower Colorado River (Table 10) (Conine et al. 1978).

TABLE 9.--Breeding bird community parameters of four riparian woodlands and their adjacent areas in Arizona (Goldberg et al. 1979)

Habitat1 Standing Bird Location Species

D . 3 4 Crop 5 Species Type Richness ens1ty Visitors Biomass Diversity

Ash Creek 21 19(84)2

310 25 21,022 2.70 Ash Creek (E) 8 52 25 1,666 1.89 Ash Creek (W) 5 24 27 2,243 1.56 Rucker Canyon 19 22 (41) 328 17 16,320 2.95 Rucker Canyon Adj. 4 34 19 1,089 1.33 Turkey Creek 23 24(54) 503 21 39,646 2.90 Turkey Creek (E) 7 99 19 3,529 1. 75 Turkey Creek (W) 6 57 15 3,166 1.58 Wet Beaver Creek 18 21(52) 359 14 29,370 2.87 Wet Beaver Adj. 5 80 16 2,338 1.56

1 2see Table 1. Numbers in parenthesis are ~he percentage of bird species censused regularly in

the a~jacent habitats.

4Pairs per 40 hectares.

5Number of irregular summer species. Grams per 40 hectares.

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TABLE 10.--Riparian species lost with agricultural encroachment (Conine et al. 1978).

Yellow-billed Cuckoo ·(coccyzus americanus) Black-chinned Hummingbird (Archilochus alexandri) Anna Hummingbird (Calypte anna) Yellow-bellied Sapsucker (Sphyrapicus varius) Brown Creeper (Certhia familiaris) Hermit Thrush (Catharus guttatus) Western Bluebird (Sialia mexicana) Blue-gray Gnatcatcher (Polioptila caerulea) Cedar Waxwing (Bombycilla cedrorum) Phainopepla (Phainopepla nitens) Bell Vireo (Vireo bellii) Lucy Warbler~mivora luciae) Yellow-breasted Chat (Icteria virens) Indigo Bunting (Passerina cyanea) Evening Grosbeak (Hesperiphona vespertina) Pine Siskin (Carduelis pinus) Lawrence Goldfinch (Car~s lawrence!) Green-tailed Towhee (Pipilo chlorurus) Rufous-sided Towhee (Pipilo erythropthalmus) Black-throated Sparrow (Amphispiza bilineata)

RECREATIONAL USE

Riparian zones are important to wildlife because they(!) have increased floral diversity and structure,(2) contrast dramatically with the surrounding upland vege­tation, and (3) have a large amount of edge (Thomas et al. 1979). People are also attracted to these areas by the hydrological and vegetational characteristics, and by the high densities and diversities of wildlife.

Recreational use negatively affects riparian bird populations directly through disturbance and indirectly by trampling, gathering of firewood, soil compaction, etc. (Aitchison 1977, Thomas et al. 1979). Steve Loe (personal communication) of the Coronado National Forest, Arizona expressed deep concern for the impact of birders using tape recorders to attract coppery-tailed trogons at the south fork of Cave Creek. This activity was banned in hopes of increasing trogon p~oductivity. Breed­ing bird density and diversity decreased relative to a control site after the opening of a campground in Oak Creek Canyon, Arizona (Table 11)(Aitchison 1977).

TABLE 11.--Effects of a campground before and after opening on the breeding birds of a ponderosa pine-mixed deciduous riparian habitat (Aitchison 1977).

Bird Species Diversity

Year

1973 1974 1975

Campground Before After

2.19 2.62 2.19

413

1.15 2.42 2.34

Control Before After

2.08 2.08 1.83

2.34 2.43 2.71

I .

TABLE 11 (cont'd.)

Density 1973 297 178 326 366 (Prs/40 ha) 1974 297 223 158 297

1975 178 257 178 445

Species Richness 1973 12 8 9 12 1974 16 13 8 12 1975 10 12 7 17

OVERGRAZING

Overgrazing is almost universally thought to have a severe negative impact on riparian vegetation (Brown et al. 1977, Ames 1977). The effects of overgrazing on riparian habitats are twofold. First, overgrazing in the adjacent watersheds in­creases the likelihood of torrential flooding; and second, overgrazing eliminates the understory herbaceous layer and stand reproduction (Brown et al. 1977, Davis 1977). On segments of Sonoita Creek, Arizona, where cattle have grazed for at least 50 years, the combination of decreased establishment and normal mortality of the mature trees would eventually either severely reduce in number or eliminate cottonwoods from this forest (Glinski 1977). Bird densities, diversities and species numbers will undoubtedly be negatively affected by these long term changes in habitat structure. Songbird/raptor use and diversity increased 350% within an enclosure along Big Creek, Utah as c0mpared to outside grazed areas after four years (Duff 1979). Stevens et al.(1977) found that adjacent, nonriparian habitats which were not heavily grazed supported a higher migrant passerine density and migrant passerine species diversity than those areas which were more heavily grazed. To date, no grazing plan short of complete removal of livestock by fencing has had any significant effect on riparian habitat (Ames 1977, Davis 1977, Dahlem 1979).

HABITAT ISLANDS

Riparian habitat types usually are linear, lying along water courses and blend­ing into one another along an elevational gradient. However, clearing of many ripar­ian areas has left islands of riparian habitat. There are also riparian islands around localized water sources such as springs and wells. The stze of bird popula­tions within a given riparian island depends on both the size of the island and its distance from areas of similar habitat (Johnson et al. 1977). For example, in homogeneous Fremont cottonwood stands along the Verde River, Arizona, breeding bird densities ranged from 425 to 847 pairs/40 ha and include 20 to 26 species (Table 2) (Carothers 1974); while a similar but isolated riparian habitat (1.6h~at Indian Gardens, Grand Canyon National Park, supported only 10 breeding species with a total density of 198 pairs/40 ha (Stevens et al 1977).

CONCLUSIONS AND RECOMMENDATIONS

Within the southwestern United States there is an impressive variety of riparian vegetative associations. Within each association there is a unique avian community influenced by type of vegetation, structure, density, temporal fluctuations, adjacent habitats, recreational use, grazing, location and other factors. In such a multi­dimensional system it is difficult to develop any generalized management guidelines. Compounding the problem is the fact that our current level of knowledge of bird communities is only at the inventory level for many vegetative associations.

414

Factors that should be considered when implementing any riparian management plan include: (1) base plans on bird populationsoccurring in all seasons, not merely on breeding bird populations; (2) manage riparian and adjacent areas as a unit; (3) elim­inate or greatly decrease grazing; (4) grazing and timber management practices on adjacent watersheds should be conducted in such a ways as to avoid torrential flooding (Brown et al. 1977); (5) provide for controlled recreational use.

Additional specific information is needed to develop management guidelines for the bird communities of each vegetative association, in order to reasonably predict the impact of varying degrees of habitat manipulation and use on the riparian birds of the southwest. Riparian habitats should be managed as the most sensitive and productive North American habitat because of their high value to avian populations.

LITERATURE CITED

Aitchison, Stewart W. 1977. Some effects of a campground on breeding birds in Arizona. In Importance,

preservation and management of riparian habitat: A symposium. R. Roy Johnson and Dale A. Jones, tech. coord. p. 175-182. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Anderson, Bertin W., Ronald W. Engel-Wilson, Douglas Wells, and Robert D. Ohmart. 1977a. Ecological study of southwestern riparian habitat: Techniques and data

applicability. In Importance, preservation and management of riparian habitat: A symposium. R.JRoy Johnson and Dale A. Jones, tech. coord. p. 146-155. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Anderson, Bertin W., Alton Higgins, and Robert D. Ohmart. 1977b. Avian use of Saltcedar communities in the Lower Colorado River valley.

In Importance, preservation and management of riparian habitat: A symposium. ~Roy Johnson and Dale A. Jones, tech. coord. p. 128-136. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Anderson, Bertin W., and Robert D. Ohmart. 1977a. A vegetation management study for the enhancement of wildlife along the

lower Colorado River. U.S. Bureau of Reclamation Lower Colorado River Region. Boulder City, Nevada.

Anderson, Bertin W., and Robert D. Ohmart. 1977b. Vegetation structure and bird use in the lower Colorado River valley.

In Importance, preservation and management of riparian habitat: A symposium. ~Roy Johnson and Dale A. Jones, tech. coord. p. 23-34. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Anderson, Bertin W., and Robert D. Ohmart. 1976. Wildlife use and densities report of birds and mammals in the lower

Colorado River valley. U.S. Bureau of Reclamation Lower Colorado River Region. Boulder City, Nevada. 278 pp.

Ames, Charles R. 1977. Wildlife conflicts in riparian management:

preservation and management of riparian habitat: and Dale A. Jones, tech. coord. p. 49-51. USDA RM-43. Rocky Mt. For. and Range Exp. Stn., Fort

Atwood, Jonathan.

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1978. Willow woodland-freshwater marsh. Amer. Birds 32(1):95.

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Austin, George T. 1970. Breeding birds of desert riparian habitat in Southern Nevada.

Condor 72(4):431-436. Barker, Harriette W.

1979. Riparian woodland-live oak-juniper. Amer. Birds 33(1):84-85. Bottorff, Richard, Nancy Hurley, Jo Trainor, and Hugh Kingery.

1973. Floodplain cottonwood forest. Amer. Birds 27(6):996-997. Bottorff, Richard L., Nancy Hurley, Urling Kingery, Douglas Stotz, Jo Trainor, and Hugh Kingery.

1974. Floodplain cottonwood forest. Amer. Birds 28(6):1036-1037. Brown, David E., Charles H. Lowe, and Janet F. Hausler.

1977. Southwestern riparian communities: Their biotic importance and management in Arizona. In Importance, preservation and management of riparian habitat~ A symposium. JR. Roy Johnson and Dale A. Jones, tech. coord. p. 201-211. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Brown, David E., Charles H. Lowe, and Charles P. Pase. 1979. A digitized classification system for the biotic communities of North

America, with community (series) and association examples for the southwest. J. Ariz.-Nev. Acad. Sci. 14(Suppl. 1):1-16.

Cardiff, Eugene, Steven Cardiff, and K. H. Berry. 1978. Tamarisk-desert riparian. Amer. Birds 32(1):105-106.

Carothers, Steven W., and R. Roy Johnson. 1975. Water management practices and their effects on nongame birds in range

habitats. In Proceedings of the symposium on management of forest and range habitats for-nongame birds. Dixie R. Smith, tech. coord. p. 210-222. USDA For. Serv. Gen. Tech. Rep. W0-1, Washington, D.C.

Carothers, Steven W., R. Roy Johnson, and Stewart W. Aitchison. 1974. Population structure and social organization of southwestern riparian

birds. Amer. Zool. 14(1):97-108. Conine, Kathleen H., Bertin W. Anderson, Robert D. Ohmart, and Jeff F. Drake.

1978. Responses of riparian species to agricultural conversions. In Strategies for protection and management of floodplain wetlands and other riparian eco­systems. R. Roy Johnson and J. Frank McCormick, tech. coord. p. 248-262. USDA For. Serv. Gen. Tech. Rep. W0-12. Washington, D.C.

Dahlem, Eugene A. 1979. The Mahogany Creek watershed-with and without grazing. In Forum-Grazing

and riparian/stream ecosystems. Oliver B. Cope, ed. p. 31-34. Trout Unlimited, Denver, Colo.

Davis, Gary A. 1977. Management alternatives for the riparian habitat in the Southwest. In Impor­

tance, preservation and management of riparian habitat: A symposium. R. Roy Johnson and Dale A. Jones, tech coord. p. 59-67. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky .Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Duff, Donald A. 1979. Riparian habitat recovery on Big Creek, Rich County, Utah. In Forum-Grazing

and riparian/stream ecosystems. Oliver B. Cope, ed. p. 91-92. Trout Unlimited, Denver, Colo.

Engel-Wilson, Ronald W. and Robert D. Ohmart. 1978. Floral and attendant faunal changes on the lower Rio Grande between Fort

Quitman and Presidio, Texas. In Strategies for protection and management of floodplain wetlands and other riparian ecosystems. R. Roy Johnson and J. Frank McCormick, tech. coord. p. 139-148. USDA For. Serv. Gen. Tech. Rep. W0-12. Washington, D.C.

Evens, Jules. 1979a. Mesquite community. Amer. Birds 33(1):93-94.

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Evens, Jules. 1979b. Desert Riparian thicket. Amer. Birds 33(1):90-91.

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Gaines, David A. 1973. Floodplain riparian woodland •. Amer. Birds 27(6):995.

Gaines, David A. 1977. The valley riparian forest of California: their importance to bird popula­

tions. In Riparian forests in California their ecology and conservation. Anne Sands, ed. p. 57-86. Inst. Ecol. Publ. No. 15, Davis, CA.

Gavin, Thomas A., and Lyle K. Sowls. 1975. Avian fauna of a San Pedro valley mesquite forest.

J. Ariz. Acad. Sci. 10(1):33-41. Glinski, Richard L.

1977. Regeneration and distribution of sycamore and cottonwood trees along Sonoita Creek, Santa Cruz County, Arizona. In Importance, preservation and management of riparian habitat: ~ symposium. R. Roy Johnson and Dale A. Jones, tech. coord. p. 116-123. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Goldberg, Nancy H. 1979. Behavioral flexibility and foraging strategies in Cassin's and Western King­

bird's (Tyrannus vociferans and l· verticalis) breeding sympatrically in riparian habitats in central Arizona. Unpublished Ph.D. dissertation. University of Illinois, Urbana-Champaign.

Goldwasser, Sharon. 1978. Desert riparian-freshwater marsh and ponds. Amer. Birds 32(1):113-114.

Gundy, Thomas R., and Patricia A. Flanagan. 1978. Sycamore-Coast Live Oak riparian woodland. Amer. Birds 32(1):84-85.

Hanka, Ladislav R. 1979. Floodplain cottonwood 'forest. Amer. Birds 33(1):82.

Hehnke, Merlin, and Charles P. Stone. 1978. Value of riparian vegetation to avian population along the Sacramento river

system. In Strategies for protection and management of flood plain wetlands and other riparian ecosystems. R. Roy Johnson and J. Frank McCormick, tech. coord. p. 228-235. USDA For. Serv. Gen. Tech. Rep. W0-12. Washington, D.C.

Hubbard, John P. 1977. Importance of riparian ecosystems: Biotic considerations. In Importance of

riparian habitat: A symposium. R. Roy Johnson and Dale A. Jones, tech. coord. p. 14-18. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Hurley, Nancy, Hugh Kingery, Jo Trainor, and Richard Bottorff •. 1971. Floodplain cottonwood forest. Amer. Birds 25(6):966-967.

Hurley, Nancy, Urling Kingery, and Hugh Kingery. 1977. Floodplain cottonwood forest. Amer. Birds 31(1):71.

Hurley, Nancy, Urling Kingery, Douglas Stotz, Jo Trainor, and Hugh Kingery. 1975. Floodplain cottonwood forest. Amer. Birds 29(6):1125.

Ingles, Lloyd G. 1950. Nesting birds of the willow-cottonwood community in California.

Auk 67(3):325-332. Jehl, Joseph R., Jr.

1978. Mesquite woodland. Amer. Birds 32(1):102. Johnson, R. Roy, Lois T. Haight, and James M. Simpson.

1977. Endangered species vs. endangered habitats: A concept. In Importance, pre­servation and management of riparian habitat: A symposium. R. Roy Johnson and Dale A. Jones, tech. coord. p. 68-79. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Justice, Frank, Jan Justice, Hugh Kingery, and Urling Kingery. 1979. Floodplain cottonwood forest. Amer. Birds 33(1):81-82.

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Justice, Frank, Jan Justice, Urling Kingery and Hugh Kingery. 1978. Floodplain cottonwood forest. Amer. Birds 32(1):83-84.

Kingery, Hugh, and Richard Bottorff. 1972. Floodplain cottonwood forest. Amer. Birds 26(6):980.

Koopman, Richard W. 1979. Desert oasis woodland II. Amer. Birds 33(1):90.

Loveless, Bob, and Ruth Loveless. 1978. Sycamore-Coast Live Oak riparian woodland. Amer. Birds 32(1):84.

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Manolis, T. 1973. Disturbed floodplain woodland. Amer. Birds 27(6):994-995.

McCallum, D. Archibald. 1979. Mixed-mesophytic canyon bottom. Amer. Birds 33(1):86-87.

McKernan, Robert L. 1978 •. Willow riparian. Amer. Birds 32(1):85.

McKinnie, Ian R., Jr. 1974. Sycamore-Coast Live Oak riparian woodland. Amer. Birds 28(6):1036.

Pase, Charles P., and Earle F. Layser. 1977. Classification of riparian habitat in the Southwest.

vation and management of riparian habitat: A symposium. and Dale A. Jones, tech. coord. p. 5-9. USDA For. Serv. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins,

Rappole, J. H., and D. W. Warner.

In Importance, preser­R. Roy Johnson Gen. Tech. Rep. Colo.

1976. Relationships between behavior, physiology and weather in avian transients at a migratory stopover site. Oecologia 26(2):193-212.

Rotenberry, J. T., R. E. Fitzner, and W. H. Rickard. 1979. Seasonal variation in avian community structure: differences in mechanisms

regulating diversity. Auk 96(3):499-505. Stamp, Nancy E.

1978. Breeding birds of riparian woodland in south-central Arizona. Condor 80(1):64-71.

Stevens, Lawrence E., Bryan R. Brown, James M. Simpson, and R. Roy Johnson. 1977. The importance of riparian habitat to migrating birds. In Importance, pre­

servation and management of riparian habitat: A symposium. R. Roy Johnson and Dale A. Jones, tech. coord. p. 156-164. USDA For. Serv. Gen. Tech Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Szaro, Robert C. and Russell P. Balda. 1979. Bird community dynamics in a ponderosa pine forest. Stud. in Avian

Biol. 3:1-66. Thomas, Jack Ward, Chris Maser, and Jon E. Rodiek.

1979. Riparian zones in managed rangelands - Their importance to wildlife. In Forum-Grazing and riparian/stream ecosystems. Oliver B. Cope, ed. p. 21-31. Trout Unlimited, Denver, Colo.

Waner, Roland H. 1977. Significance of Rio Grande riparian systems upon the avifauna. In

Importance, preservation and management of riparian habitat: A symposium. R. Roy Johnson and Dale A. Jones, tech. coord. p. 165-174. USDA For. Serv. Gen. Tech. Rep. RM-43. Rocky Mt. For. and Range Exp. Stn., Fort Collins, Colo.

Weinstein, Michael, and K. H. Berry. 1978. Tamarisk-saltbush. Amer. Birds 32(1):106.

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418