j. Field Ornithol., 65(1):8-16

PREDATIONF•RICA H.

OFBIRDSATFEEDERSDUNN • AND DIANEINWINTER

L. TESSAGLIA

CornellLaboratoryof Ornzthology
159 SapsuckerWoodsRoadIthaca, New York 74850 USA

Abstract.--A continentwidesurveyof homeswith bird feedersproduced567 reportsdocumenting1138 incidentsof predation.Of the 25 speciesof predatorsrecorded,three (SharpshinnedHawk, Accipiterstriatus;domesticcat;Cooper'sHawk, A cooperil)were responsiblefor 80% of the incidentsin which the predatorwas known. Ten of the 62 speciesof prey
identifiedaccountedfor 92% of all victims.The birds most vulnerableto predationwere
thosethat commonlyoccurat feedersthroughoutthe continent(i.e., the most widespreadspecies),but additionally, flocking specieswere more vulnerable to avian predatorsthanmore solitaryones.Prey sizewas correlatedto sizeof avian predators,but catsconcentrated
on smallbirds.Hawks wereattractedto feederswith particularlyhighlevelsof bird activity,
but catswere not. The bird-feedingenvironmentdoesnot appearto exposebirdsto a higher
risk of predationthan is encounteredin the absenceof feeders.
DEPREDACI•)NDE AVES EN COMEDEROS DURANTE EL INVIERNO

Sinopsis.--Sehizo una encuesta,a nivel continental,en residenciasen dondese les proveede coinederosa aves,que produjo567 informesen loscualessedocumentan1138 incidentes
de depredaci6n.De las 25 especies
de depredadoresinformadostresde fstos,a saberAccipiterstriatus,A. cooperziy el gato domfstico,fueron responsablesdel 80% de los incidentesen
donde el depredadorfue identificado.Diez de las 62 especiesque sirvieron como presas,
formaron el 92% de todaslas vlctimas.Las avesmils vulnerablesa la depredaci6nfueron
aquellasque mils comfinmenteutilizan coinederosartificialesa nivel continental(ej. lasespeciesmils ampliamentedistribuidas).No obstantelas avesque se alimentan en grupos
resultaronmils vulnerablesque las que lo hacende forma solitaria.E1 tamafiode la presa
se correlacion6al tamafiodel depredador,aunque los gatosconcentraronsusesfuerzosenaves pequefias.Los halconesfueron atraidosa coinederos,con altos nivelesde actividad
aviar,mientrasque ocurri6lo opuestoconlosgatos.Losambientesendondehay coinederos
artificialesno parecenexponeralas avesa un riesgomayorde depredaci6n,queen lugaresen donde fistos no se encuentran.

The backyard bird feeder is often a sceneof predation, and feeder
ownerssometimesworry that they are drawing birds away from a safer
natural environmentto onewhere densebird concentrations
and relatively
open habitat may increasethe risk of predation.
A surveyof mortality at feeders,conductedduring the winter of 19891990, shedslight on the links betweenpredationand bird feeding,as wellas providinginformationon predators'choiceof prey species.Data wereprovidedby participantsin ProjectFeederWatch,a continentwidesurveyof winter

birds at feeders.
METHODS

Participantsin ProjectFeederWatchwere providedwith specialforms
on which they couldrecordany bird or mammal deathsoccurringin their
Currentaddress:
CanadianWildlifeService,NationalWildlifeResearchCentre,Hull, Quebec
K I A OH3, Canada.

Vol.6•,No.1

Predatzon
at BzrdFeeders

FIGURI•1.

[9ProjectFeederWatchRegionsmentionedin text.

yards. For predation deaths, information was requestedon speciesof
predator and of prey taken, date and time of the incident, and behaviorof predatoror prey.
FeederWatchparticipantsalsowatchedtheir feedersfor 1 or 2 d during
eachof 10 2-wk periodsfrom 11 Nov. 1989 through 6 Apr. 1990 ("countperiods";seeDunn 1992 for details). For each bird speciesobservedat
their feeders,FeederWatchersrecordedthe peak number of individuals
seenduring eachcountperiod. Numbers of birds, and informationon thecharacteristicsof the bird-feeding site (e.g., habitat, number of feeders,
type of food offered) were recordedon computer-readableforms.
For analysispurposes,the continentwas divided into eight Regions(Fig. 1). FeederWatchparticipantswere distributedthroughoutthe populatedregionsof the continent,but the majority (70%) were in the Northeast. For each species,the "mean number per feeder" (annual averagepeak number of individualsper feedersite) was calculatedas a geometricmean to normalize distributionsskewedby a few feederswith exceptional
activity.Continentalmeansare averagevaluesfrom smallerunits(usuallystates).

Sample sizesvary throughoutthe paper becausecaseswere excluded
that lackedinformation relevantto a given analysis.

10]

E. H. DunnandD. L. Tessaglia

J.Field
Ornithol.
Winter1994

Bird identification skills of FeederWatch participants as a group arevery good(judgingfrom resultsof our species-editingprocedures),andwe considerour resultsfor the frequentlyobservedpredatorand preyspeciesto be highly reliable.
RESULTSOf the 5500 Project FeederWatch participants who submittedobservationsfor the winter of 1989-1990, 567 (10%) also reported incidentsof predation.At sitesthat reportedpredation,there was an averageof
2.0 predationdeathsper site during the 4-mo period DecemberthroughMarch. At homes reporting mortality from any cause, there was anaverageof 1.0 predation death per site.
Most participants (67%) reported a single predation event, and 94%
of casesinvolvedfour or fewer incidentsduring the winter. The remaining
6% of participants accountedfor 29% of all predation events,with anaverageof just over 10 incidentseach.
Sharp-shinnedHawk (Accipiterstriatus)was the top-rankedpredator,responsiblefor 35% of all predation deathsin which the predator wasidentified.The domesticcat ranked second,causing29%. Cooper'sHawk(A. cooperil)and Sharp-shinnedHawk togetherwere implicated in 51%of cases,including those in which the observer could not distinguishbetweenthe two species.The three next-mostfrequentpredators(Redtailed Hawk, Buteojamaicensis;American Kestrel, Falcosparverius;andMerlin, F. colurnbarius)
were implicatedin only 12% of cases.Altogether,
these six most-commonpredators accounted for 90% of all predation
deathsin which the predator was identified.
The remaining 10% of kills were made by 19 other predators,each ofwhich was implicatedin lessthan 2% of all incidents:four hawks (Northern Harrier, Circuscyaneus;Northern Goshawk,Accipitergentilis;RedshoulderedHawk, Buteolineatus;Broad-wingedHawk, B. platypterus),
two owls (Great Horned Owl, Bubovirginianus;Northern Pygmy Owl,Glaucidiumgnoma); Northern Shrike (Lanius excubitor);six other birds(Greater Roadrunner,Geococcyx
californianus;
Scrub Jay, Aphelocoma
coerulescens;Black-billed Magpie, Pica pica; American Crow, Corvus
brachyrhynhos;
European Starling, Sturnusvulgaris;Common Grackle,Quiscalusquiscula);four mammals (dog, Canisfamiliaris--mainly one
individual that ate House Sparrows;fox, Vulpessp.; woodrat, Neotoma
sp.;shorttailweasel,Mustelaerminea),and two snakes(rattlesnake,Crotalussp.; and probable garter snake, Tharnnophissp.).
Sites with reports of cat predation suffered a winter averageof 2.3
birds killed, whereasthosereporting hawk predation averaged1.9 birds
killed. The differencewas not significant.(Mann-Whitney U-test, n =125, 392; P -- 0.776). Few sites(3.8%) reportedpredationboth by catsand hawks.

Neither cat nor raptor predation was reported from all FeederWatch
Regionsin the sameproportionas the number of participantsliving thereVol.65,No.
1Predatmn
at BtrdFeeders[1 1(cats: X2 = 62.9, n = 306, P < 0.001; hawks: X2 = 28.5, n = 619, P <0.001).
Incidentsof cat predation were distributedevenlyover the four wintermonthsDecemberthrough March (X2 -- 4.2, n = 129, P = 0.243). Deaths
causedby Cooper'sand Sharp-shinnedHawks peakedearly in the winter,however,with 40% of casesin December, 19% in January, 26% in February and 15% in March (X2 = 42.5, n = 286, P < 0.001).

Predatorattackswere spacedequally amongthree 3-h time blocksfrom
0800 to 1700 hours (hawks: x 2 = 5.3, n = 209, P = 0.071; cats:X2 = 4.9,
n = 37, P = 0.085). Sharp-shinnedand Cooper'sHawk activity (combined)tendedto peak in the middletime block,mainly dueto a noticeablerise in incidentsbetween 1200 and 1300 hours. Cat predation dropped
by half in the latest time block, but sample sizes were too small todemonstratesignificance.
Ten speciesof prey accountedfor 92% of all victims (Table 1). An
additional 52 prey specieswere identified, including four mammals, but
none constitutedas much as 2% of all prey items. Every one of the preyspecieshas been recordedtaking food from feedersat least occasionallyby ProjectFeederWatch.Most (85%) visitedat least 15% of the feeders
within a FeederWatch Region during the winter of 1989-1990.
Prey choiceof the five most commonavian predatorsdependedpartly
on size (Fig. 2). Predator weight (average of male and female mass;
Dunning 1984) was positivelycorrelatedwith mean weight of identified
prey (r = 0.983, n = 5, P < 0.01). Cats, although heavy themselves,
concentratedon lighter prey.
Another factor in prey choicewas speciesdistributionand abundanceat feeders.Among regular feedervisitors(thoserecordedat 15% or moreof feedersacrossthe continent), the number of each specieskilled (including zeros) was directly related to how widespreadthat specieswas(in termsof percentageof feedersvisited:r = 0.72; n = 28; P < 0.001).
In addition,the speciescommonlytaken by avian predators(Table 1)
hadhigherpeakcounts(i.e., greatertendencyto flock)than lesscommonly
taken speciescountedby FeederWatchers(5.4 vs. 2.8 birds per peakcount,n = 22 species,t-test,P < 0.031). This was not true for cats.Peak
countsof each speciesand the percent of feedersthey visited were notcorrelatedwith each other (r = 0.33; n = 28; P < 0.331).
The sum of the annual averagepeak countsfor the ten most common
prey specieswas higher at sites that reported hawk predation than atsitesthat did not report any predation (59.7 vs. 38.7, n = 178, 3722;
t-test P < 0.001). There was no suchdifferencebetweensiteswith andwithout cat predation (43.6 vs. 38.8, n = 53, 3720; t-test P < 0.183).
(Samplesizesdo not total 5500 becausemany participantshad incomplete
records for the winter).

Sites that reported deathsby avian predatorswere more likely thanthose without avian predators to have these characteristics:deciduous
woodlotswithin 0.8 km of the feedingstation(42% of homeswith deaths
vs. 32% of other homes), a large feeding area (75% vs. 65%), many12]

E. H. DunnandD. L. Tessaglia

J.FieldOrnithol.
Winter 1994

Vol.65,No1Predation
at B•rdFeeders[136.05.5

5,0-4,5 '4.0-$.5-$.0-

2.0-

1.5

AMKE

SS A

MERLC HARTHACAT

(•5)

(•40)

(•85)

(440)

(•25)

(4500)

MAINPREDATORS(GM)FIGURE2. Box plotsof weight of prey taken at feeders(weightsfrom Dunning 1984).
Symbols:+ = mean,horizontalline = median,wide bar includes75% of observations,and vertical line showsentire range. Codesfor predators:AMKE = American Kestrel,
SSHA = Sharp-shinnedHawk, MERL = Merlin, COHA = Cooper'sHawk, RHTA
= Red-tailedHawk.

plantingsin the yard (86% vs. 81%), year-roundfeeding(68% vs. 58%),
more than six feeders(76% vs. 54%), and more than five typesof food(categorizingwater, sugar water, suet and each seedtype as a separate
food; 68% vs. 56%; x2 tests;rz = 345, 4863; all P's < 0.05).
Sites reporting cat predation were more likely than siteswithout cat
predationto offer food on the ground (47% of homeswith deathsvs. 37%
of other homes)and to have less-specializedbird feedingpractices.For
example, they were lesslikely to serveniger, suet or peanuts,and more

likely to offer suet/seedmixes. They were also, not surprisingly,more
prone to having frequent visitsby cats(91% vs. 66%), and perhapsas aconsequence,
were lesslikely to have squirrelsat their feeders(62% vs.
73ø70).

14]

E. H. DunnandD. L. Tessaglia

J.Field
Ornithol.
Winter1994

DISCUSSION

Avian predatorswere attractedto feederswith high levelsof activity.
Hawks took individuals more frequently than expectedfrom flocking
speciesthat alsofeedreadily on the ground,behavioraltraits that perhaps
make prey especiallyconspicuousfrom the air. Sitesthat reportedavian
predatorshad more of these flocking speciesat their feedersthan did
other sites, probably as a result of habitat characteristicsthat enhance
feeder visitation (i.e., year-round, more-specializedand larger feeding
programs, and well-treed habitat in the vicinity).
By contrast,cat predation was not associatedwith any habitat characteristicsthat would particularly enhancebird activity. Siteswith predationcausedby catshad relativelyunspecializedfeedingprograms,few
plantingsnearby, and more groundfeedingwhen comparedto siteswithout cat predation. Unlike hawks, catswere not more activeat siteswhere
the common prey specieswere most numerous. As territorial predators,
the cats appear to concentrateon whatever is locally available, whereas
the avian predators move to the most active sites.
Raptor predationwas reportedmore often than expectedin the Southwestand West CoastRegions,where Sharp-shinnedand Cooper'sHawks
are especiallycommonin winter (Root 1988). Predationrateswere lower
in the Northeastthan expectedon the basisof numbersof projectparticipants there. Overall there was a decline in hawk predation after

December,and thisprobablyreflectscompletibnof migrationaway fromthe feeder-rich north. Cat predation was also high in the Southwest,
perhapsdue to mild weather allowing catsmore time outdoorsin winter.
We found a mid-day peak in accipiterattacks,but this may havebeen
an artifact. Many feederownerswatch their yards more closelyover thelunch hour. Other studiessuggestthat, at leaston migration, Sharp-shins
hunt mainly in early and late hours of the day (Palmer 1988).
The averagenumber of predation deathsper site (from siteswhereparticipantsreportedwitnessingany type of mortality) was 1.0 birds per
winter. This figure is obviouslyvery imprecise.If the severalthousand
activeFeederWatchparticipantswho failed to report any deathsactually
did not seeany predation, the true rate of predation at feedersis much
lower than 1.0 bird per site per winter. On the other hand, the chancesof a feeder owner missinga predation event are quite high. Attacks arebrief and rarely causenoise that would attract house occupants.Cat
predation is often detectedonly if the cat presentsprey to its owners.
Moreover, somepeoplewho witnessedpredationmay not have submitted
mortality reports.We have no basisfor judging the relative importanceof thesebiases.It is clear, however,that homeswithout any bird feeders
at all will suffer a far lower rate of predationthan reportedhere.
Nonetheless,we doubt that bird feedingcauseshigher predationmortality than would be found in more natural settings.Only 2% of sites
reportingavian predationrecordedmore than 10 deaths(maximum fromonesitewas 37), whereas67% reportedonly onedeath.A Cooper'sHawk,

Vol65,No1

Predat•on
at BzrdFeeders

however,probably needsto eat at least 120 small birds over the courseof a winter (1-3 prey items per day in the size range of birds taken atfeeders;Palmer 1988). Although somefeedersare certainly a regularsourceof food for resident hawks, most are evidently raided only inpassing.

Avian predationcan sometimes
havea significantimpacton smallbird
populations.One studyestimatedthat 10% of finchespassingthrougha
migratorystopoversite were killed by predatorsin autumn (Lindstrom1989), and up to 30% of juvenile tits (Parus spp.) were killed in thenestingseasonby Sparrowhawks(Accipiternisus;Perrins and Birkhead1980). Our figures suggestthat avian predation at feedersduring thewinter has a lower impact. The averageFeederWatchcount for the 10
mostpreyed-uponspeciescombinedwas 59.7 birds for siteswith avianpredators,and the averagelossto thosepredatorswas 1.9 birds. Even if
our predationrate of 1.0 bird per winter is a severeunderestimate,avian
predatorsmust be killing the majority of their prey elsewhere.
As hawksmustkill to survive,bird mortality from raptor attacksshould
not increaseoverallbecausebird feedingis becomingmorecommon,unlesseasyaccessto food on migrationor in winter causesraptor populations
to increase.Evidencefrom the Breeding Bird Survey, however, showsthat neitherSharp-shinnednor Cooper'sHawk populationshavechanged
significantlyduringthe period1966-1989 (S. Droege,pers.comm.).
Cat predationcan also have a significanteffect on bird populations,and the toll appearsto be highest in residential areas (Churcher andLawton 1987, Coman and Brunner 1972, Hubbs 1951, McMurray andSperry 1941). Cats take whateverprey is mostavailable,and the lawns
and lack of understoryin suburbiahave low small mammal populations
and relativelyvulnerablebirds. Churcher and Lawton (1987) estimatedthat a significantproportionof annual mortality in House Sparrows(Passerdomesticus)
in an English village was causedby well-cared-for
house cats. There was no overall decline in the local House Sparrow
populationover the 1-yr period of the study,however.The highestproportionof birdsin the diet occurredin mid-winter, whenthe total numberof prey caughtwas at a minimum. Another peak of bird prey camein
May and June, when fledglingswere available (Churcher and Lawton
1987; see also Hubbs 1951).
Individual catsin Churcher and Lawton's (1987) studyvaried widelyin their huntingpropensities,andkill ratesdeclinedascatsaged(Churcherand Lawton 1987). Our study,too, showedthat a relativelysmall proportion of housecatscausedfrequent deathsat feeders(only 4% mademore than 10 kills per winter).
Cats with stronghunting propensitiesmay kill just as many birds inthe absenceof feedersas when they are present.It is very probable,
however,that bird feeding tempts other catsto mount attacks,too. The
impactof this "extra" mortality on bird populationsis difficultto assess.
Certainly the prey speciesmost frequentlyinvolvedare commonandwidespread.Studiesin rural areasindicatethat birds are taken much less16]

E. H. DunnandD. L. Tessaglia

J.Field
Ornithol.
Winter 1994

frequentlyby cats(Coman and Brunner 1972, Hubbs 1951, McMurrayand Sperry 1941). Predation rates from predominantly suburban sites(this study, Churcher and Lawton 1987), should not be extrapolatedto
all environments.

Someevidencesuggeststhat feedersmay actuallyproviderelativelysafe
havensfrom predation. There are more individual birds on hand to bealert and soundalarms (Popp 1988, Siegfriedand Underhill 1975, Waite1987). Moreover, food supplementsmay reduceforagingtime and, concurrently,the periodsof maximum exposureto predators(Janssonet al.
1981).
ACKNOWLEDGMENTS

We would like to thank the thousandsof peopleacrossNorth America who participatedin Project FeederWatch. This study would not have been possiblewithout their dedicateddata-collection
efforts.Thanks alsoto ColleenLynch for her essentialadministrativesupport
to the Project.ProjectFeederWatchis coordinatedby the Cornell Laboratoryof Ornithology(Ithaca,New York, USA) and by the Long Point Bird Observatory(Port Rowan,Ontario,Canada).
LITERATURE

CITED

CHURCHER,P. B., ANDj. H. LAWTON. 1987. Predation by domesticcatsin an English
village. J. Zool. 212:439-455.
COMAN,B. J., ANDH. BRUNNER. 1972. Food habitsof the fetal housecat in Victoria. J.
Wildl. Manage. 36:848-853.
DUNN, E. H. 1992. Bird mortality from striking residentialwindowsin winter. J. FieldOrnithol.

64:302-309.

DUNNING,J. B., JR. 1984. Body weightsof 686 speciesof North American birds. West.
Bird Banding Assoc.Mongr. 1:1-38.
HUBBS,E.L. 1951. Food habitsof fetal housecatsin the SacramentoValley. Calif. FishGame

37:177-189.

JANSSON,C., J. EKMAN,ANDA. VONBROMSSEN.
1981. Winter mortalityand foodsupply
in tits Parus spp. Oikos 37:313-322.
LINDSTROM,A. 1989. Finch flocksizeand risk of hawk predationat a migratorystopoversite. Auk106:225-232.

MCMURR^Y, F. B., ^ND C. C. SPERRY. 1941. Food of feral house cats in Oklahoma--aprogressreport. J. Mammal. 22:185-190.

PALMER,R. S., ED. 1988. Handbook of North American birds. Vol. 4: diurnal raptors(Part I). Yale Univ. Press,New Haven, Connecticut.433 pp.
PERRINS,
C. M., ANDT. R. BIRKHEAD.1980. The effectof Sparrowhawkson tit populations.

Po??,J.W.

Ardea

68:133-142.

1988. Scanningbehaviorof finchesin mixed-species
groups.Condor90:510-512.

ROOT,T. 1988. Atlas of wintering North Americanbirds.Universityof ChicagoPress,Chicago,Illinois. 312 pp.
SIEGFRIED,W. R., ANDL. G. UNDERHILL. 1975. Flockingas an anti-predatorstrategy
in doves. Anita.

Behav.

23:504-508.

W^ITE, T.A. 1987. Vigilance in the White-breastedNuthatch: effectsof dominanceandsociality.Auk 104:429-434.

Received1 Dec. 1992; accepted18 Feb. 1993.