58 CAITHNESS, WILI.IAMS AND BtH.!.; BIRDS AND AIRCRAFT

BIRDS AND AIRCRAFT: A PROBLEM ON SOME

NEW ZEALAND AIRFIELDS

T. A. CAITHNESS, M. J. WILLIAMS and R. M. BULL

New Zealand Wildlife Service, Department of Internal A flairs, Wellington

] NTRODUCTION

Since technology enables man to assert at leastsome control over most features of his environmentit is surprising that in the planning of engineeringprojects the only features considered seriously arephysical ones. Biological complications are oftenignored until they become a problem and in thisthe aviation industry is no exception.Recent advances in aircraft design and corres-

ponding increases in air-speed have, along withincreases in the population of some birds, particu-larly gulls, emphasised a problem, always apparentbut not previously considered important; that ofthe risk of collision belween birds and aircraftExamples such as the Boston Bay tragedy in

October 1960 when, as the result of a collisionwith a flock of starlings, a turbo-prop Electracrashed with loss of 62 lives (Aircraft AccidentReport 1962). have helped to convince aviationauthorities and airline pilots of the need for urgentresearch into the bird hazard on airfields.New Zealand airlines have a record almost free

of serious incidents involving birds. althoughapproximately 0.03 % of all commercial aircraftmovements in 1965-66 recorded either strikes ornear misses. As would be expected, those airfieldswilh the greatest number of movements had themost incidents; but when computed on Ihe basis ofincidents per aircraft movement we find that someairfields had up to 1.0% of movements affected,Of the totaL 48% occurred at take-off, 36% atlanding and 16% at other phases of flight near theairfield (calculated from data supplied by theDepartment of Civil Aviation).Although advanced aircraft design has increased

the severity of the bird problem, the siting ofairfields is also an important contributing factor.Because airfields occupy large areas, marginal landsuch as swamps and sand-dunes is often chosenas sites and frequently parts of estuaries arereclaimed. Within New Zealand many airfieldshave been built in such areas.Because of increasing bird strikes and the result-

ing increased maintenance costs, scientific investi-gations into birds as a hazard to aircraft beganoverse.as about] 957. Since that time, in New

Zealand, an additional international airport hasbeen built and several secondary airfields havebeen reconstructed,

ANALYSIS OF THE PROB!.EM

The new international airport at Auckland(Fig. I) was built on a site where apparentlylittle thought was given to the presence of largeDopulations of birds. Indeed, there are few areasin the country which support a larger summerpopulation of wading birds than Manakau Har-bour. Hawkes Bay airport, Napier (Fig. 2), wasrecently reconstructed on a site immediatelyad iacent a large breeding colony of black-backedgu1ls (Larus dominicanus). a rubbish 'dump, awildlife refuge, a lagoon and the sea. Invercargillairport (Fig. 3) is built on a reclaimed swamp atthe head of an extensive estuary. Its environs arepoorly drained and these, with the estuary andnearby rubbish dump. serve as a rich feedingground for waders, waterfowl and gulls. As far asbirds arc concerned, these airfields could hardlyhave been built in more attractive areas. As wellas providing sites for airfields. marginal land nearcities is used for activities which would be offensivewilhin the urban precincts, e,g.. rubbish dumps,sewage farms and outfalls, abattoirs and pig farms.All Ihese attract birds. Of the twelve problemairfields in New Zealand, each had, at the start ofIhis investigation in 1964, one or more of theabove activities nearby.Determination of factors influencing the presence

of birds requires a separate ecological study ofeach airfield. Although each has its own particularproblems, there are some possessed in common;(i) Extensive ungrazed grass areas offer an idealhabitat for a large and varied insect population,To insectivorous species such as starlings (Sturml.\'vulgaris). banded dotterels (Charadrius hicinctus)and in some areas, South Island pied oystercatchers(Haematopus ostralegus finschi) and magpies(Gymnorhina sp.), such rich feeding grounds area great attraction, Other than during thebreeding season some, or all, of the abovespecies-and others - have been recorded feedingthroughout the day in large numbers.

CAITHNFSS. WII.I.IAMS AND BULl.; Bums AND AIRCRAFT 59

(ii) Grass has so far been regarded as virtuallyessential on airfields for it binds the surface andtraps dust. Some airfields have grass runways ascross-wind alternatives to the main runway.

The grasses typically encouraged are brown-top(Agrostis tenuis) and Chewings fescue (Festucarubravar.commutata). Couch (Agrop.vron repens)and Pua prutensis are also common. Severalother grasses are used depending on local condi-tions: for drier areas, Bermuda grass (Cynodondactylon), dryland brown-top (Agrostis sp.) andNotodanthonia semiannularis; in damp areas J>oatrivialis and creeping bent (Agrostis sto!onifera),All these are frec-seeding and thus allract sced-

~

eating birds. important amongst which are spar-rows (Passer domesticus). greenfinches (Chlorischloris) and goldfinches (Cardue!is curdue!is bri-tannica) .

Most birds which feed consistently on airfieldsare highly social and it is their flocking habits thatpresent the greatest danger.

(iii) Nearby feeding areas also creale a problem.Airports such as Auckland. Nelson and Taurangaare near or extend on to large shallow harboursystems and the mud-flats exposed at low tidesprovide feeding grounds for waders. The habits ofthese birds at low water do not pose a hazardbut at high water their flight paths to and fromroosts frequently intersect those of aircraft.

(iv) Waterfowl are another group found in asso-ciation with swamp, lake or lagoon; but as theflights of waterfowl are mainly confined to dawnand dusk, their activities. like those of waders. areto some extent predictable.

General aspects of the problem posed by birdson airfields in New Zealand can best be illustratedby reference, in some detail, to the situations atAuckland. Napier and Invercargill.

Auckland

Auckland International Airport. Mangere (Fig.I), has a finger-like reclamation projecting on tothe mudflats of Manakau Harbour. It is flankedto the south and west by these and to the east bythe large tidal Pukaki Creek. The mudflals sup-port one of the largest concentrations of wadersfound in New Zealand. The activity of the wadersis largely governed by the tides, and at high waterfeeding areas are inundated and the birds forcedto seek a roosting site. For this, in the absence ofany deterrent action, the airfield reclamationapparently proves ideal (Saul 1967).

FIGURE I. Auckland International Airport andenvirons. (a) Tidal mud flats. (b) Permanent

water. (c) Wader movement.

Nearby lies Wiroa Island - already used as aroost by waders during small to medium high tides.In an effort to remove the birds from the airfield,roosting facilities at Wiroa Island were improved.This improvement consisted of building a reclama-tion some five acres in extent above the height ofthe highest tides. Fresh water pools. a salt-waterlagoon and windrows were formed. As grass grewto cover favoured bare areas on the airfield. thebirds chose to use the Wiroa roost instead. How-ever, because the major feeding grounds near theairport lie to the north, and Wiroa roost is to thesOClth, bird flight across the airport reclamationremains as a lesser hazard. This flight is predict-able within broad limits according to the times andheights of high water; the bigger the tide. thegreater the number of birds which fly to Wiroa ?s

MANUKAU

HARBOUR

60 CAITHNESS, WILLIAMS AND BULL: BIRDS AND AIRCRAFT

progressively more of the roosts close to the feed-ing grounds are swamped. Wader flight becomesan acute problem when numbers build up in latesummer prior to migration.. Movements of communally-roosting species toand from their roosts at dusk and dawn offeranother hazard: red-billed gull (Larus novaehol-landiae scopulinus) and black.backed gull flightpaths along Pukaki Creek take them directly acrossthose of aircraft.Feeding on this airfield is not the problem it is

at some others. This is mainly because the birdsare constantly harassed and the grass maintainedat a height of four to six inches. (Overseas reportssuggest that long vegetation inhibits the activitiesof the more social spxies such as starlings andthis seems to be so at Mangere). However, whatmay discourage one species may indirectly encour-age another. Longer grass is apparently goodhabitat for mice (Mus musculus) and, althoughthese rodents are not a direct danger to aircraft.harrier hawks (Circus approxim~ns gouldi) andwhite faced herons (Notophoyx novaehollandiae)that may hunt them over the airfield probably are.

NapierHawkes Bay Airport, Napier (Fig. 2), has a

problem different from Mangere in that the con-cern here is mainly with the flight pattern ofbreeding black-backed gulls and the evening flightsof starlings and waterfowl, mainly mallard ducks(A nas p. platyrhynchos) and black swans (Cygnusatratus).The airfield is constructed on the Ahuriri Plain

which, prior to a six-foot uplift by the 1931 Napierearthquake, was a shallow tidal lagoon about fourmiles long and two miles wide. A narrow lagoonnow flanks the Ahuriri Plain to the south and west,and to the east lies Hawke Bay. An extensivesystem of open drains dissects the entire area anda small lagoon which forms part of the WestshoreWildlife Refuge adjoins the south-eastern boundaryof the airfield.Commonly found in the open water is a multi-

tude of waders and waterfowl. Swans and ducksare particularly numerous during the game seasonin May and persist in the area until pairing takesplace in July. It is their characteristic eveningflights from the refuge to other feeding areas nearthe airfield that causes concern.Starlings are present throughout the year but

their numbers are noticeably greater outside theairfield. This is because the airfield pasture is poorand hence supports only a moderate insect fauna;whereas the surrounding farmland with its richturf offers a uniformly rich fauna for food.

FIGURE2. Napier Airport and environs.

Four hundred yards north was a large breedingcolony of approximately 2,500 black-backed gulls.All aircraft, regardless of wind direction, had topass low over the area occupied by the colonyand although strikes occurred occasionally, withas many as II birds killed at one time, no seriousdamage to aircraft was sustained. Beyond thebreeding seaSon - which usually extends fromJuly (when preliminary nesting behaviour begins)until late February (when the last chicks arefledged) - a large number of these gulls remainedin the area feeding on the Napier City Councilrubbish dump a little further north; this attrac-tion has now been removed.

As at Mangere, flights to and from roosting sitescause concern and here starlings and black-backedgulls are involved - the former roosting in treesdirectly south and the latter on the edge of thelagoon to the south-west.

This airfield was modified in 1963-64 to allowuse by jet-prop aircraft and it could well be thathad full consideration been given at that time tothe bird problem, an alternative site might havebeen sought.

CAITHNESS. WILJ.IAMS AND BIILL; BIRDS AND AIRCRAFT

FIGURE 3. Invercargi/J Airport and environs. (a)

Open drain. (b) Residential and industrial area.(c) Tidal mudflat. (d) Open water.

lnvercargill

Invercargill Airport (Fig. 3) is situated on partof a reclaimed lake and swamp at the head of theNew River estuary. Here. in contrast to Mangereand Napier. the problem is primarily one of birdsfeeding on the airfield. Drainage is so poor thatgrass overlies a layer of moss three inches thickand the surroundings include many pockets ofopen water and large drains.Throughout the entire area and on adjacent

farmland is a very high population of Wi.<ean"(Porina) and it is the larval form of this moth thatforms the major food item of the insectivorousbirds which abound. Farming and the grazing ofstock appear to discourage birds from feeding onthe farmland; but the airfield is comparativelyundisturbed and therefore constantly supports

large numbers of feeding South Island pied oyster-catchers, red-billed and black-billed gulls (Laru.1bulleri) and starlings.

Tidal influence on bird numbers is noticeable.abundance is greatest at high tide. At spring tidesnumbers reach a peak which indicates that theairfield and adjacent paddocks are used also forroosting at these times. An increase in waders andgulls is particularly noticeable in stormy southerlywealher, to which most other roosing sites in theestuary are ex posed.

The problem with waterfowl at Invercargill issimilar to that at Napier with many birds livingin the nearby open water.

Black-backed, red-billed and black-billed gulls~

constantly "trade" between the Invercargill cityrubbish dump, barely three-quarters of a milesouth-east of the airfield and two freezing works,four and a half and eight miles north respectively.This constant movemenl intersects aircraft flightpaths.

Twilight flights of the three species of gull totheir roosts also cause concern.

REMEDIES

The solutions which an ecologist offers to thebird hazard problem must be - (a) short-term tocorrect the immediate situation and (b) long-termto prevent repetition and to offer some form ofprediction.

Besides this he must try to make his recom-mendations economically acceptable. He mustalso try to infringe as lillIe as possible on presentpatterns of airport management, for, naturally.airport authorities are reluctant to alter existingpractices. Nevertheless, this will sometimes benecessary. In this respect the problem is partlya human one, as man, the most adaptable of allcreatures, often expects birds alone to change theirways.

Among short-term solutions used in this coun-try, quite the most dramatic was the poisoning ofthe gull colony in Napier in November 1965(Caithness, in press) - a measure that will becontinued in forthcoming seasons to remove suc-ceeding age classes as they return to their ancestralbreeding ground. We must stress, however, that inmost instances killing of birds on a scale greatenough to solve the problem will not be possible.The Napier poisoning was practical only becauseof the well-defined breeding colony and it is almost

61

62 CAITHNESS, WILI.IAMS AND BULl.; BIRDS AND AIRCRAFT

certain that once the colony is completelydestroyed, the bird problems there will be solvedas far as black-backed gulls are concerned.

Black-backed gulls roosting on grass adjacent torunways have proved troublesome and to discour-age them favourable results have been achievedby placing "crucified" carcases (those with wingsoutstretched) on these areas. As a refinement.polystyrene models have proved equally effectiveand have the advantage of being more durable.Pyrotechnics such as carbide bird scarers, Verycartridges and shot-gun blanks all have a use butare best used in conjunction with some otherstimulus. such as distress calls. By themselves,these particular remedies have little long-termeffect as habituation to them soon occurs. Fur-thermore, response appears dependent upon theintensity of the bird's drive to remain in the area,i.e., with gulls the drive to breed and often to feedin a particular area is strong whereas there isa lesser drive to loaf or roost in anyone place(Seubert 1965). On Ihe other hand, with speciessuch as starlings, roosting is more specific to anarea than the other drives.

Long-term solutions are invariably costly forthcy basically involve some form of major modi-fication of the environment. For example. toeliminate waterfowl their habitat must be removed.This in most instances calls for extensive drainageor filling or both.

The problem of discouraging social feeders onairfields is a difficult one but long grass approxi-mately nine inches high is a fairly efficient deter-rent. There are, however, several drawbacks toestablishing such a sward - the present grass mix-ture used on airfields in New Zealand is made upof free-seeding species difficult to maintain at asuitable height all year round. Furthermore, duringsummer the dry leaves might present a fire hazard,particularly where pure jets are operating. A longsward might also have an adverse effect on drain-age and thus reduce the bearing characteristics ofoff-runway areas (Cooke-Smith 1963) and mightalso reduce the braking efficiency of aircraft; butthe main criticism by aviation authorities is thatrunway lighting would be obscured. By raisinglights an extra few inches, by providing betterdrainage in the first place and by exchanging thepresent grass mixture for a non-seeding species.these difficulties could be resolved.

To remove the insectivorous birds effectivelytheir source of food must be removed. Control ofsoil insects is not enough - complete elimination

should be the goal. This requires the applicationof insecticides at rates of up to ten times those usedin agriculture, thus creating a problem of toxicresidues in run-off water, especially in inadequatelydrained areas close to cities or concentrations ofwildlife. Detailed study of drainage patterns isnecessary before the use of insecticides can bepermitted; and insecticides should be sought thatare not readily leached from the soil. Investiga-tions along these lines are at present under wayat Wellington Airport where the dye fluorescein isbeing used to get some idea of the level of con-tamination to be expected from drainage into thesea.

The provision of artificial roosts such as con-structed at Mangere is another possibility in thoselocalities where the airport is at present serving asa roost. Careful siting will be important, for birdsShODldnot be drawn across aircraft flight paths.

The natural environment often resists man'sefforts to expand his habitat and the air is noexception. Though the ecologist can offer solu-tions to some aspects of the problem, the unfor-tunate siting of several New Zealand airfields inrelation to large and varied bird populations willmake it most difficult to obtain a satisfactorylevel of control. In the planning of airfieldsconsiderations of bird ecology must, in future, playan important part.

ACK NOWl.EIJGM ENTS

The writers wish to thank Dr G. R. Williams and MrE. K. Saul, Wildlife Service, Wellington, for helpfulcriticism of this paper.

REfERENCES

AIRCRAFT ACCIDENT REPORT. Civil Aeronautics Board.U.S.A. SA-358. 31 July 1962.

CAITHNESS, T. A., 1967. Poisoning of gulls with aJpha-chloralose near a New Zealand airfield (in press).

COOKE-SMITH.R. A. W.. 1963. Method of clearing birdsfrom United Kingdom civil aerodromes. In Leprobleme des oiseaux sllr les aerodromes: 131-35.lnst. Nat. Recherche Agronom. Paris.

SAUL. E. K.. 1967. Birds and aircraft: a problem atAuckland's new international airport. J. Roy. Aero~Ill/ilt. Soc. 71: 366-376.

SEUBERT.J. L., ]965. Biological studies of the problem ofbird hawrd to aircraft. Dept. Interior, Div. Wild I.Res., Washington, D.C. June 1965,22 pp. 3 figs.