Bald Eagles Consume Emperor Geese During Late&Hyphen;Winter in the Aleutian Archipelago

MARCH 2004 SHORT COMMUNICATIONS 81

LITERATURE CITED study of postmortem findings in Red-tailed Haw_ks.J RaptorRes. 30:7-14. DEEM, S.L., S.P. TER•I.I., AND DJ. FORRESTER.1998. A KE•N, D. 1981. The incidence of man-caused and nat- retrospectivestudy of morbidity and mortality of rap- ural mortalities to raptors. RaptorRes. 15:108-112. tors in Florida: 1988-1994. J. Zoo Wildl. Med. 29:160- SWEENEY,S.J., P.T. REDIG,AND H.B. TORDOFF.1997. Mor- 164. bidity, survival, and productivity of rehabilitated Per- DUKE, G.E., P.T. R•DIG, ANDW. JONES.1981. Recoveries egrine Falconsin the upper midwesternU.S.J. Raptor and resightingsof releasedrehabilitated raptors. Rap- Res. 31:347-352. t0r Res'. 15:97-107. ZAR,J.H. 1996. Biostatisticalanalyses. Prentice Hall, Up- FIX, A.S. raNDS.Z. B•tROWS. 1990. Raptors rehabilitated per Saddle River, NJ U.S.A. in Iowa during 1986 and 1987: a retrospectivestudy. J. Wildl. Dis. 26:18-21. Received 14 August 2002; accepted 20 August 2003 FR•NSON,J.C., N.J. THOMAS,M.R. SMITH,A.H. ROBBINS, Associate Editor: Marco Restani S. NEWMAN,AND P.C. MCCaTIN. 1996. A retrospective

j RaptorRes. 38(1):81-85 ¸ 2004 The Raptor ResearchFoundation, Inc.

BALD EAGLES CONSUME EMPEROR GEESE DURING LATE-WINTER IN THE ALEUTIAN ARCHIPELAGO

MAPm A. P•cc• • U.S. GeologicalSurvey, Western Ecological Research Centeg, I ShieldsAvenue, University of California, Davis, CA 95616 U.S.A.

ROBERT G. ANTHONY U.S. GeologicalSurvey, Oregon Cooperative Fish and WildlifeResearch Unit, OregonState University, Corvallis, OR 97331 U.S.A.

JEFFREYC. WILLIAMS U.S.Fish and WildlifeService, Alaska Maritime National WildlifeRefuge, Aleutian Islands Unit, 2355 KachemakBay Drive, Homg AK 99603 U.S.A.

KEYWORDS: Bald Eagle, Haliaeetus leucocephalus;Em- winter ecology of Emperor Geese is poorly understood perorGoose, Chen canagica;food habits'; Alaska; Aleutian Ar- due in part to the extremely remote nature of the Aleu- chipetago. tian Archipelago (Petersen et al. 1994). Bald Eagles (Haliaeetusleucociphalus) are ubiquitous, Emperor Geese (Chen canagica)are a speciesof con- year-round residentsthroughout the most of the Aleutian cern becausetheir population has declined rapidly since Archipelago (Murie 1959) and obtain most of their prey the mid-1960s and continues to remain below manage- from the nearshoremarine environment (Anthony et al ment objectives (Petersen et al. 1994). Emperor Geese 1999). We predict that Bald Eaglesshould prey on win- are restrictedprimarily to Alaskaand exhibit an east-west tering Emperor Geeseif availablebecause eagles depre- migration pattern, wherebymost birds begin breeding on date other speciesof geesein southern latitudes (Frenzel the Yukon-Kusko_kwimDelta by mid-May, stage on the and Anthony 1989, Watson et al. 1991, McWilliams et al Alaska Peninsula by late September,and migrate west- 1994). However, the existing information on Bald Eagle ward to winter in the Aleutian Archipelagofrom late No- predation of Emperor Geeseappears contradictory. Sher- vember to mid-April (Eisenhauerand Kir_kpatrick1977, rod et al. (1976) suggestedgeese may be too large for Petersenet al. 1994). Demographicand movementstud- Bald Eaglesto kill efficiently,and other studiesrarely re- •es have been conducted on breeding grounds and stag- ported Emperor Geese as Bald Eagle prey in the Aleu- mg areas (e.g., Schmutz et al. 1994, 1997); however,the tians (Murie 1940, White et al. 1971, Shetrod et al. 1976) Conversely,Eisenhauer and Kirkpatrick (1977) stated that Bald Eaglesare perhaps the dominant avian preda- • Email address:[email protected] tor of wintering Emperor Geese, and cite the observa- 82 SHOUT COMMUN]C^T•ONS VOL. 38, No. 1

ALASKA

•Akun

AleutianArchipelago • /•' • UnalaskaAkutan

Kiska / ,• lia Amchitka Tanaga Adak

0 500 kilometers

L J

F•gure 1. Map of the Aleutian Archipelagoindicating islandswhere Bald Eagle nest surveysoccurred, April-May 2000-01.

tions of Williamson et al. (1975) of frequent eagle pre- counted prey remains from occupied neststhat appeared dadon of Emperor Geese on Amchitka Island in the to be from the current year's nesting attempt, which ex- western Aleutian Archipelago. Furthermore, Gill and cluded remains that appeared obviouslyweathered and I/ancheloe (1993) observedBald Eaglesdepredating Em- deeply soiled.We identified most unknown prey remmns by comparison with museum specimenshoused at the peror Geese on the Alaska Peninsula.Because almost the Alaska Maritime National Wildlife Refuge, Adak, AK. entire population of Emperor Geesewinters in the Aleu- We calculatedthe percent of Bald Eagle nestscontinn- tian Archipelago, a need for information on sourcesof ing prey remains, and then the percent of those nests winter mortality exists (Gill and Kincheloe 1993). Em- containing Emperor Geese remains by island and year peror Geese have relativelylow overwinter survivalcom- We estimated Bald Eagle diets by dividing the minimum pared to other goose species,which may play a pivotal number of prey items for each prey taxa by the total role in their demography(Schmutz et al. 1994, 1997). number of prey items acrossall islandsand years. Herein, we describeBald Eagle diets and the occurrence of Emperor Geeseremains in Bald Eaglenest sitesduring RESULTS late winter-early spring. We visited 94 Bald Eagle nests during the course of ME'I HODS our study. Sixty percent (N = 18) of these nests contained prey during 2000, and 89% (N = 57) during 2001. We surveyed nesting eagles on Unalaska, Akutan, Akun, and Adak islandsfrom 15 April-3 May 2000, and No Bald Eagle nestswith prey remains contained any Amlia, Adak, Tanaga, Amchitka, and Kiska from 20 identifiable Emperor Geese remains during 2000. How- April-28 April 2001 (Fig. 1). We surveyedca. 1150 km of ever,39% (N = 22) of nestswith prey remainscontained shoreline from inflatable skiffs with at least two observers identifiable remains of Emperor Geeseduring 2001. Em- wsuallysearching fbr nestingeagles. Our surveyscoincid- peror Geese were most frequent (eight of 15 nests) on ed roughly with the onsetof Bald Eagle egg laying (Shet- Kiska, which was the •nost western island sampled in our rod et al. 1976) and the end of the Emperor Gooseover- study.Emperor Geese occurred in five of 13 nestswith winteringperiod (Eisenhauerand Kirkpatrick1977). We searched a maximum of 16 climbable nests per island. prey remains on Tanaga, four of 13 nestson Amchitka, We searched for prey remains in and around nests and three of 12 nests on Adak, and two of four nests on Am- recorded the minimum number of individual prey items lia. (Mollhagen et al. 1972, Anthony et al. 1999). We only We collected 191 prey items comprising 19 identifiable MARCH 2004 SHORT COMMUNICATIONS 83

20%

16%

•0%

PrayTaxa '

Figure 2. Percent of individual prey items from 191 total prey items found in Bald Eagle nestsin the Aleutian Archipelago,April-May 2000-01.a a Scientificnames of prey taxa not mentioned in text: Northern Fulmar (Fulmarusglacialis), Rock Ptarmigan (Lagopus mutus), cormorant (Phalacrocoraxspp.), murre (Uria spp.), auklet: (Aethiaspp.), Black-leggedKittiwake (Rissatridac- tyla), Atka mackerel (Pleur0grammusmonopteryg4us), long-nosed lancet fish (Alepisaurusferox), Ancient Murrelet (Synth- hboramphusantiquus), puffin (Fraterculaspp.), Common Raven (Corvuscorax), Snow Bunting (Plectrophenaxnivah•), shorebird(Scolopacidae). Other waterfowlinclude Mallard (Anasplatyrynchos), Northern Pintail (A. acuta),Harlequin Duck (Histrionicushistrionicus), Red-breasted Merganser (Mergusserrator), and unknown waterfowl.

and three unidentifiable prey taxa, indicating that Bald suchas alcidsand procellariformesavailable during sum- Eaglesconsumed a varietyof prey during our study.How- mer (White et al. 1977, G. Byrd and J. Williamsunpubl ever, the distributionof identifiable prey items in eagle data). Mammalian prey also are relatively scarcebecause d•ets was skewedtowards Glaucous-winged Gulls (Larus introduced hares (Lepusspp.) occur only in the eastern glaucescens)and Emperor Geese,which composed21% Aleutians, and sea otters (Enhydralutris) have experi- and 12% of all prey items, respectively(Fig. 2). All other enced a 75-88% decline throughoutthe Aleutians (Do- identifiable avian and mammalian prey composed<5% roff et al. 2003). Thus, Emperor Geese may be an im- of all prey items. Fish occurred infrequentlywith the ex- portant alternative winter food source for Bald Eagles, ception of Pacific cod (Gadus macrocephalus).Fish and regardlessof how they are acquired (i.e., predation or mammalian prey were usuallyidentifiable to species,but scavenging).Emperor Geeseare availableto Bald Eagles 21% of all prey items consistedof unidentifiable avian becausethey inhabit protected nearshore reefs and la- prey. goons where eagles forage (Petersen et al. 1994). The harshAleutian winter and lack of agriculturalfoods avad- DISCUSSION able to most other speciesof wintering geesein southern Emperor Geeseremains occurred in Bald Eagle nests latitudes may weaken Emperor Geese (Schmutz et al and were the second most frequent prey item in Bald 1994), thereby further increasing their vulnerability to Eagle diets. Bald Eagleslikely consumedmost of these predation or eventual scavengingby Bald Eagles.How- geeseat the end of their overwinteringperiod. Our ob- ever,we cannot determine the absolutefrequency of Em- servations provide empirical evidence that Bald Eagles peror Geesein Bald Eagle diets from our data because consume Emperor Geese more extensivelythan previ- birds and large bony fish are often over-representedin ouslyreported, and help resolveconflicting accounts of samplesof prey remains collectedfrom eaglenests (Todd Bald Eagle predation on Emperor Geesein the literature. et al. 1982, Mersmann et al. 1992), and a high proportion However, the absolutemagnitude of eagle predation is of unknown birds occurred in our sample. unknown becausewe cannot partition depredated from Emperor Geese remains did not occur in Bald Eagle scavengedEmperor Geese. nestssearched during 2000. Temporal variation in Bald Bald Eagle diet breadths are likely constrained Eagle nesting chronologylikely explainsyear-year differ- throughout winter and early spring becauseof the ab- ences.Eagle nesting was delayed apparently in the east- senceof anadromousfish and severalspecies of seabirds ern Aleutians during 2000 because only 26% of eagle 84 SHORT COMMUNICATIONS VOL. 38, NO. 1 pmrsnested by late April-earlyMay (R. Anthonyunpubl. their logistical support and expertise throughout the data). Spring migration of Emperor Geeseusually peaks study,and to M. Single and J. Ackley of Natural History by mid-April(Eisenhauer and Kirkpatrick1977), soEm- New Zealand LTD, and the crew of the R.S.V. Evohe for providing ship supportduring 2000. We also thank the peror Geeselikely migratedbefore eaglesbegan to nest. Ounalashka Corporation for permission to accesstheir Conversely,83% of eagle pairs surveyedin the central lands on Unalaska. A.K. Miles, G.V. Byrd, D. Buehler, B. and western Aleutians during 2001 nested by late April, Gill, R. Jackman,M. Petersen,K. Phillips, and two anon- thus increasingthe probabilitythat depredated or scav- ymousreviewers provided constructive reviews on earlier enged Emperor Geesewould be brought back to eagle drafts of the manuscript. nest sites and detected in our searches. Reported nesting densitiesof eaglesin the Aleutians LITERATURE CITED range from one pair per 7-20 km of coastline(G.Byrd ANTHONY,R.G., A.K. MILES,J.A. ESTES,AND F.B. ISMCS. andJ. Williams unpubl. data), and we observedover 350 1999. Productivity,diets, and environmentalcontam- breeding pairs during our surveys(R. Anthony unpubl. inants in nesting Bald Eagles from the Aleutian Ar- data). Assumingthat (1) eagledensities are similardur- chipelago.Environ. Toxicol. Chem. 18:2054-2062. ing winter which is reasonablegiven that adultsin the DOROFF,A.M., J.E. ESTES,M.T. TINKER,D.M. BURN,and Aleutiansare likely non-migratory(Murie 1959, White et T.J. EVANS.2003. Sea otter population declinesin the al. 1971), although sub-adultmovements are largely un- Aleutian Archipelago.J. Mammal. 84:55-64. known; (2) our resultsare representativeof consumption EISENHAUER,D.I., ANDC.M. KIm{PATRICIC1977. Ecology of Emperor Geeseby Bald Eaglesduring the entire over- of the Emperor Goose in Alaska. Wildl. MonogzNo wintering period for Emperor Geese;and (3) at least 57. some proportion of geese are depredated rather than FRENZEL,R.W. ANDR.G. ANTHONY.1989. Relationshipof scavenged,Bald Eaglesmay contribute more to Emperor Goose mortality than previouslythought. diets and environmental contaminants in wintering Bald Eagles.J. Wildl.Manage. 53:792-802. RESUMEN.--Lascausas de mortalidad del ganso empera- Gn,L,R.E.,JR. AND K.E. KINCHELOE.1993. Are Bald Eagles dor migratorio (Chencanagica)una especie de manejo es- important predatorsof Emperor Geese?J. RaptorRes 27:34-36. pecial en Alaska,se conocenpobremente. Evaluamos la relativafrecuencia del consumopot parte del aguilacalva MCW•LLIAMS,S.R., J.P DUNN, AND D.C. RAVELING.1994 (Haliaeetusleucocephalus) de gansosemperadores a lo lar- Predator-preyinteractions between eaglesand cack- go de las islasdel archipidago Aleutiano, identificando ling Canada and Ross'sGeese during winter in Cali- restosde presasde 94 nidos de ftguilascalvas durante fornia. Wilson Bull. 106:272-288. Abril-Mayo, 2000-01. Encontramospartes no identifica- MERSMANN,TJ., D.A. BUEHLER,J.D. FRASER,AND J.K. SEE- bles de gansosemperador en el nido de aguilascalvas OAR.1992. Assessingbias in studiesof Bald Eaglefood con restos de presas (N = 18) durante 2000. Inversa- habits.J. Wildl.Manage. 56:73-78. mente, 39% de los nidoscon restosde presas(N = 57) MOLLHAGEN,T.R., F.J. WILEY,AND R.L. PACK;am.1972. contertiangansos emperador durante 2001. E1ganso em- Prey remainsin Golden Eagle nests:Texas and New perador constituy612% de todoslos item presaindivi- Mexico.J. Wildl.Manage. 36:784-792. duales encontrados en los nidos de ftguila calva durante MURIE,OJ. 1940. Food habits of the northern Bald Eagle 2000-01. Aunque nuestrosm6todos no pueden distin- in the Aleutian Islands, Alaska. Condor42:198-202. guir depredaci6nde alimentaci6npor carrofiay los res- ß 1959. Fauna of the Aleutian Islands and Alaska tos de presafueron evaluadosal final del periodo de so- peninsula.N. Am. Fauna 61:1-364ß bre invernaci6n del Ganso emperador, las ftguilascalvas PETERSEN,M.R., J.A. SCHMUTZ,AND R.F. ROCICWELL.1994 pueden ser una fuente significativade mortalidad para Emperor Goose (Chencanagica). No. 97. LnA. Poole el gansoemperador durante el invierno en las islasAleu- and F. Gill [EDS.], The birds of North America. Acad- tianas.Ademf•s, el gansoemperador puede ser un com- emy of Natural Sciences,Philadelphia, PA and Amer- ponente importantede la dieta para lasaguilas calvas que ican Ornithologists'Union, Washington,DC U.S.A. pasanel invierno en los mismosterritorios donde se re- SGItMUTZ,J.A., S.E. CekNTOR,AND M.R. PETERSEN.1994 produjeron. Seasonal and annual survival of Emperor Geese.J [Traducci6n de C6sar Marquez] Wildl. Manage.58:525-535.

, R.E ROCKWELL,AND M.R. PETERSEN.1997. Relative ACKNOWI,EDGMENTS effects of survivaland reproduction on the popula- This studywas funded by the U.S. Navy 'CLEAN' pro- tion dynamicsof Emperor Geese.J. Wildl.Manage. 61 gram. M. Murphy provided support from the Navy. We 191-201. thank E. Forsmart, G. Keister, M. Law, E.C. Meslow, and SliERROD,S.K., C.M. WroTE, AND F.S.L. WILLP•MSON.1976. M Rutishauserfor their assistancewith eagle surveysand precariousnest climbs.We extend gratitude to the staff Biologyof the Bald Eagle on AmchitkaIsland, Alaska of the AlaskaMaritime National Wildlife Refugeand crew Living Bird 15:143-182. of the U.S. Fish and Wildlife Service's M/V Ti•lax for TODD, C.S., L.S. YOUNO,R.B. OWENJR., AND FJ. GRAM- MARCH 2004 SHORT COMMUNICATIONS 85

LICH. 1982. Food habits of Bald Eagles in Maine. J. faunal Investigations.Pages 227-260 in M.L. Merritt Wildl. Manage.46:636-645. and R.G. Fuller [EDs.], The environment of Amchitka WATSON,J.W., M.G. GARVmTr,AND R.G. ANTHONY.1991. Island, Alaska. National Technical Information Ser- Foraging ecologyof Bald Eaglesin the Columbia Riv- vice, Springfield, VA U.S.A. er estuary.J. Wildl. Manage.55:492-499. WILLIAMSON, ES.L., C.M. WHITE, AND W.B. EMISON. 1975. WHITE, C.M., W.B. EMISON, AND F.S.L. WILLIAMSON. 1971. The birds of AmchitkaIsland. Department of Zoology, Dynamicsof raptor populationson Amchitka Island, Brigham Young University,Provo, UT U.S.A. Alaska. BioScience21:623-627. --, ES.L. WILLIAMSON,AND W.B. EMmON. 1977. Avi- Received20 February 2003; accepted26 October 2003

j. RaptorRes. 38(1):85-88 ¸ 2004 The Raptor Research Foundation, Inc.

SURVIVAL AND BEHAVIOR OF A ONE-FOOTED MADAGASCAR FISH-EAGLE IN THE WILD

RUTH E. TINGAY 1 AND MICHELE L. CLARK• Schoolof Geography,University of Nottingham,Nottingham, NG7 2RD U.K.

RICHARD T. WATSON AND RUSSELL THORSTROM ThePeregrine Fund, 5668 FlyingHawk Lane, Boise,ID 83709 U.S.A.

LOUKMAN KALAVAH ThePeregrine Fund, P.O. Box 4113, Antananarivo101 Madagascar

KEYWORDS: MadagascarFish-Eagle, Haliaeetus vocifero- STUDY ARFA AND METHODS •des; amputation;dominance hierarchy; longevity. The Peregrine Fund initiated the MadagascarFish-Ea- gle ConservationProgram on Madagascar'swestern sea- board in 1991, to studythe species'ecology and breeding The ability of a one-footedraptor to survivelong-term behavior (Watsonet al. 1993). Through 2001, over 100 •n the wild hasbeen consideredquestionable (Cooper et MadagascarFish-Eagles were trapped and banded with a al. 1980, Durham 1981). While there are accounts of the uniquely numbered embossedaluminum band and a se- survivalof one-leggedraptors in captivity(Cooper 1985) ries of colored plastic or colored aluminum bands for and of those admitted from the wild to a raptor clinic individual identification. The majority of fish-eagleswere (Durham 1981), we could only locate two published ac- trapped at lakes in the Manambolomaty River floodplain countsdetailing the known survivalof one-footedraptors (19ø00'S,44ø30'E) in the Antsalovaregion of western Madagascar,ca. 300 km west of the capital, Antananarivo in the wild. Blodget et al. (1990) document the 2-yr sur- The habitat is dominated by tropical, deciduous,dry for- vival in the wild of a one-footed immature Bald Eagle est containing severallakes (with areas of 3.1-4.9 km2) (Haliaeetusleucocephalus) and Eggenhuizen (1995) docu- that support 11 fish-eagle territories (Rabarisoa et al. ments the 1-mo survivalin the wild of a one-leggedadult 1997). Eurasian Kestrel (Falcotinnunculus), killed ultimately by On 8 November 1996, a one-footed adult male Mada- •mpact with a vehicle. Avian anatomical constraints gascarFish-Eagle was trapped in a territory on Lake Be- (McKeever 1979, Cooper 1985) and species-specificfor- fotaka known as "Befotaka2." The eagle'sright foot was missing, severed at the distal tip of the tarsometatarsus, aging strategies(Cooper et al. 1980) suggestthat one- which had healed over to form a flat-basedstump mea- footed raptors have a diminishedcapacity for long-term suring30 mm X 27 min. There were no signsof infection survivalin the wild. Here, we report the 7-yr survival,in and we evaluatedthe eagle as being in otherwisegood the wild, of a one-footed adult male MadagascarFish- condition. An aluminum band (0118) was fitted to the Eagle (Haliaeetusvociferoides) and document his behavior left leg and the eagle was released.A one-footedadult and social statuswithin a polyandrousbreeding trio. male fish-eaglewith an aluminum band on its left leg was residentin the Befotaka2 territory throughout 1997 and 1998 and was assumed to be the same bird (Kalavah 1997, 1998). 1E-mail address: [email protected] During the 1999-2001 breedingseasons (May-Septemh