AND SOLUTIONS. ROBERT E. KENWARD. Institute of Terrestrial ... in heavily managed landscapes (Kenward et al. 1981) and even on moorland (Redpath and ...
j. RaptorRes.33(1):73-75 ¸ 1999 The Raptor ResearchFoundation, Inc.
RAPTOR
PREDATION
PROBLEMS
AND
SOLUTIONS
ROBERT E. KENWARD
Instituteof Terrestrial Ecology, Furzebrook Research Station,Wareham,DorsetBH20 5AS U.K.
Large raptors have probably been seen as a nuisancesincethe dawn of stockfarming. Accusations are sometimesunjustified, in that most large raptors are opportunistic scavengers.For example, more than one careful analysishas shown that lambs at nests of eagles (Aquila) were almost all scavenged.Nevertheless,other studieshave documented predation by eagleson live lambs (Murphy
tend to be local or temporary. There is no excuse for a return to widespreadpersecutionof raptors, becausethere are nowmanyother waysof avoiding
Sinclair 1990). Evidence has now accumulated that
foods, in order to maximize benefits with minimal
predation problems. Exclusion can be effectivefor reducing predation on livestockduring a shortvulnerableperiod,
for example,by penning sheepduring lambing to protectagainsteagles(Murphy 1977). In Sweden, 1977), by PeregrineFalcons(Fatcoperegrinus) on Ring-necked Pheasants (Phasianuscolchicus)are trained pigeons near lofts and during races (Tre- sometimescaught and penned in midwinter, to enleaven1977), by hawks(Acdpiter)on poultry,and surethe survivalof breedingstockthrough the late by eagles (Haliaeetus)or Ospreys (Pandionhaliae- winter period when Northern Goshawk (Acdpiter tus) at fish farms (Draulans 1987). gentilis)predation on wild pheasantstends to be Those preservinggame have long seen raptors most intense. Penning protectsagainstnonraptor as competitorsfor a harvestableresourceor even predation, too, but tendsto be expensive.A variety as a threat to the survivalof game stocks.However, of other exclusiontechniquesare availablefor use early field studieseither showedraptorstakingfew at fish farms (Draulans 1987). game (Craighead and Craighead 1956, Brfill 1964) Landscapingis extremely important, for examor that raptors and other predators were taking ple, by improving cover. Agricultural intensificamainly the diseasedor sociallydisplacedindividu- tion tends to remove cover, thus presumablyinals (Errington 1946,Jenkinset al. 1963). Earlypop- creasing prey vulnerability and reducing or ulation models suggestedthat predatorswhich de- concentratingsourcesof winter food. This may inpressedprey populationswere themselvesliable to creaseprey activity,thus again increasingvulnerabecome extinct (Gause 1934). bility, and causegatheringswhich attract raptors, Nevertheless, more recent models have shown especiallyif gameis fed artificiallyto replacescarce that predatorscan depressnumbersof a particular natural foods. Cover can often be improved both prey and still persist, either because alternative at feed sitesand on approachesto them (Mikkelprey are available or because prey numbers in- sen 1984). Nearby perchesfor raptors might also creasethrough breeding before all the predators be removed. There is scope for much more redie (Hassell 1978, Kenward and Marcstr6m 1988, searchon how game depend on cover and natural gamebird populationscan be depressedby raptors locally near nests (Eng and Gullion 1962), temporarily during irruptions (Keith and Rusch1988), in heavily managed landscapes (Kenward et al. 1981) and even on moorland (Redpath and Thirgood 1997). In Europe, renewedconcernabout raptor predation on livestock,poultry, pigeonsand game (Kalchreuter 1981) also extends to rare te-
lossof farmed land. Breeding success of game can be doubled by leavingheadlandsunsprayed(Potts 1986); perhapssimilarminor modificationscan improve survival in winter. Serious predation on game may often reflect not only recoveryin raptor populations from persecution and pollution, but alsoincreasein preyvulnerabilitythroughchanges in land management. traonids and sea birds on nature reserves. Deterrence of birds from crops and airfields is now well-developed (Murton 1971, Blokpoel SOLVING PREDATION PROBLEMS 1976). Scaringtechniquesinclude the use of disAlthough there is now evidencethat raptor pre- tresscalls,moving figures to simulate humanswith dation can causeproblemsfor wardensof domestic guns and even kites which simulate raptors. Miranimals, game and other wildlife, the difficulties rors and shell crackershavebeen tried againstrap73
74
EXPANDEDABSTRACTS
tors, but without clear evidence of success.Similar-
ly, althoughit hasbeen suggestedthat territoriality might reducepredationpressureby deterringconspecifics,this did not preventgoshawks accumulating wheremanypheasants were released(Kenward 1977). However,following early work on chemical deterrencein raptors (Brett et al. 1976) and new evidencethat someprey have developedpowerful toxinsto deter predators(Dumbacheret al. 1992), there is scopefor more studyof whether spray-on aversivescan be used to make racing pigeons or releasedgame unpalatable. Distractionof predatorsby an abundanceof alternativeprey reducesmammal predationon tetraonid broods (Marcstrtm et al. 1988). However,
VOL. 33, No. 1
spread that there is no convenientreleasearea, relocation may be an inefficient use of resources. Removal
is the alternative
to relocation.
It must
be considered, because conservation can suffer if
seriouspredation problems are ignored. Respect may be lost for conservationlaws, and birds be killed anyway,unselectively.Unfortunately, techniques preferable for selectivemanagement(i.e., live-trappingbefore shooting,and certainlyno poisoning) are the reverseof thosewhich best evade detectionif usedillegally:trapsare evidencefor all to see,whereasshootingis hard to detect and poisoningcan be done with great discretion.Raptors are now poisonedquite frequentlyin Britain (Cadbury 1990). Although strict protection can be an important tool for preserving threatened raptor populations,if treated as an ideology,it can also promote damaging conflicts. In the long term, habitat lossis probablythe biggestthreat to both raptors and game, so game conserversand raptor enthusiastsshouldbe alliesin habitatpreservation.
promoting alternative prey may also be counterproductive.For example, an abundanceof rabbits (Oryctolagus cuniculus) encouragedgoshawks to accumulate and prey heavilyon wild pheasants,possibly becausethese were a preferred prey (Kenward 1986). More studyis needed. Conservation does not benefit if conflicts divert atPreemption can be used by hunters to compete tention and resources,while agriculture and other with raptors by harvestinggame before raptor predation becomes most intense. For example, if developmentscausedevastatingland-usechanges. Nevertheless,removal of raptors should probathere is a predationpeak after vegetationdie-back bly be licensed only (1) when there is no other reducescoverin winter, shootingearlier is likely to economically acceptable technique and nothing harvest more game. worksexceptcompensationor relocation,but they Compensation can be used to offset lossesat waste resourcesbecausethe speciesis already at farms or fish hatcheries, but schemes are hard to "carrying capacity." (2) When a sustainableyield operateefficientlywithout excessive claims.An inhasbeen estimatedfor the raptor populationsuch direct form of compensation,by paying a reward as the casewhere radiotaggingshowedthat a gosfor local nestswhich fledge young, may be more hawk population in Swedenwas alreadyyielding effective, and can also be used where farm or forest 15% of itsjuveniles,which were being shot (legalactivities unwittingly destroy nests. Rewards en- ly) at farms. Nevertheless,first-year survival was courage local interest in birds and can help status much better than in ringing estimates,and the surveys.With imagination, tourism could alsocom- population was stable with many nonbreeding pensatefor frequent predation at smallsites,such adults (Kenward and Karlborn 1991). Moreover, as fish farms.
Relocationcan reduce local predation from goshawks,if they are releasedmore than 30 km from capture sites (Marcstrtm and Kenward 1981). Springnetsseton kills seemto be the ideal capture technique, becausethey are selectiveof the hawks taking poultry or game, and can only be applied effectivelywhen there really is a problem, whereas cage traps baited with pigeons catch other hawks too (Kenward et al. 1983). However, relocating trapped hawks is most practical for uncommon species,especiallyif they can be releasedin areas where populationshave been depressed.If a species is common, and predation problemsso wide-
there was no breeding at all by first-year hawks, although this occurs commonly where goshawks are below carrying capacityor adult mortality is increased. Data from such areas predicted that Swedishhawkscould havemaintaineda stablepopulation by compensatoryreduction in breeding ageif the killing increasedto 35% ofjuveniles,and could have yielded about 50% of juvenilesif shooting compensated for starvation, the other main cause of death. (3) When a removal method has
been designed to militate againstany adverseeffect. Ideally,it shouldinvolvelive-trapping,so that nontarget speciescan be releasedunharmed and target speciesneed not be killed. It should alsobe
1VIARCH1999
EXPANDED ABSTRACTS
selectiveof individuals creating the problem, and become unproductive when there is little predation. Spring nets set on kills are ideal. (4) When alternativesto killing removed birds have been adequatelyassessed. Small numbersof live birds may be useful for research, aviculture or educational
75
tor-preysystems.Princeton Univ. Press,Princeton, NJ U.S.A.
JENKINS,D., A. WATSONAND G.R. MILLER.1963. Population studieson Red Grouse Lagopuslagopusscoticus (Lath.) in northeast Scotland.J. Anim. Ecol.32:317376.
KALCHREUTER, H. 1981. The goshawk(Accipitergentilis) in Western Europe. Pages 18-28 in R.E. Kenward and I.M. Lindsay [EDS.], Understanding the goshawk.International Associationfor Falconry and Conservation of Birds of Prey, Oxford, U.K.
purposes. Supplying such birds to falconers, againstpayment of a suitable fee, might benefit conservation more than obliging falconers to pay for birds from domestic breeding schemes.Even KEITH, L.B. AND D.H. RUSCH. 1988. Predation's role •n when birds are killed, samplescan be used for pesthe cyclicfluctuationsof Ruffed Grouse.Proc. XIX ticide analysesor other forms of environmental International Ornithological Congress. monitoring. Solvingpredation problemsby remov- KENW•m),R.E. 1977. Predation on released pheasants ing raptors is very much a last resort. It requires (Phasianuscolchicus) by goshawks(Accipiter gentilis)in central Sweden. Swed. Game Res. 10:79-112. raptor enthusiaststo acknowledgethat healthyrap, V. MARCSTROMAND M. KARLBOM. 1981. Goshawk tor populations,like game birds, are a renewable winter ecology in Swedishpheasant habitats.J. Wildl. resource.By the same token, thosewith problems Manage.45:397-408. should remember that raptor predation can be beneficial too, as when nest boxes are used to in-
crease the local density of Barn Owls (Tyto alba) thereby reducing damage by rats in Malaysianoil palm plantations (J.E. Duckett, unpubl. data). LITERATURE
CITED
--.
1986. Problemsof goshawkpredation on pigeons and some other game. Proc. XVIII International OrnithologicalCongress. , M. KARLBOM ANDV. MARCSTROM. 1983. The price of success in goshawktrapping.RaptorRes.17:84-91.
--AND
V. MARCSTR(•M. 1988. How
differential
com-
petencecould sustainsuppressive predation on birds Proc. XIX International Ornithological Congress. BLOKPOEL,H. 1976. Bird hazards to aircraft. Clarke Irwin, --AND M. KA•BOM. 1991. The goshawk (Acdp•ter Ottawa, Ontario Canada. gentilis)as predator and renewable resource. Gilner BRETT,L.P.,w.g. HANKINS ANDJ. GARCIA. 1976. Prey-lithFauneSauvage 8:367-378. ium aversions: III Buteo hawks. Behav. Biol. 17:87-98. BRf3LL,H. 1964. Das Leben Dentschef Greifvbgel. Fi- MJkRCSTRtM,V. AND R.E. KENWARD.1981. Movements of wintering goshawksin Sweden.Swed.GameRes.12:1scher,Stuttgart,Germany. 35. CADBURY, J. 1990. Death by design: the persecutionof --, R.E. KENWARD ANDE. ENGREN.1988. The impact birds of prey and owlsin the UK 1979-1989.Royal of predation on boreal tetraonidsduring vole cycles: Societyfor the Protection of Birds and Nature Conan experimentalstudy.J. Anim.Ecol.57:859-872. servancyCouncil, London, U.K. MIKKELSEN, J.D. 1984. Effekt af duehoge,og andre rovfuCRAIGHEAD, J.J. ANDEC. CRAIGHEAD. 1956, Hawks, owls gle, ved fasanudsaetningsteder. Kalo ViltbiologiskStaand wildlife.Wildlife ManagementInstitute,Washingtion, Kalo, Sweden. ton, DC U.S.A.
DRAUkANS, D. 1987. The effectivenessof attemptsto reduce predation by fish-eating birds: a review. Biol. Cons. 41:219-232.
DUMBACHER, J.P, B.M. BEEHLER,T.F. SPANDE AND H.M. G•FO. 1992. The poisonous pitohui, homobatrachotoxin in the genusPitohui:chemicaldefensein birds. Sdence 258:799-801.
ENG, R.L. AND G.W. GULLION.1962. The predation of goshawks upon Ruffed Grouseon the CloquetForest Research Center, Minnesota. WilsonBull. 74:227-242. ERRINGTON, P.L. 1946. Predation and vertebrate populations. Quart.Rev.Biol.21:144-177,221-245. GAUSE,G.F. 1934. The struggle for existence. Hafner, New York, NY U.S.A.
HASSELL, M.P. 1978. The dynamicsof arthropod preda-
MURPHY, J.R. 1977. Eaglesand livestock-•somemanagement considerations.Pages307-314 in R.D. Chancellor [ED.], Proceedingsof the World Conference on Birds of Prey. International Council for Bird Preservation, Cambridge, U.K. MURTON, R.K. 1971. Man and birds. Collins, London, U.K.
POTTS,G.R. 1986. The partridge.Collins,London, U.K. SINCLMR,A.R.E. 1990. The regulation of animal populations in J.M. Cherrett [ED.], Concepts in ecology Blackwell, Oxford, U.K.
REDPATH, S.M. ANDS.J.THIRGOOD.1997. Birds of prey and Red Grouse,The StationaryOffice, London, U.K. TP,ELEAVEN, R.B. 1977. Peregrine:the privatelife of the Peregrine Falcon. Headland Publications,Cornwall, U.K.
