j. Raptor Res. 27(3):167-169 ¸ 1993 The Raptor ResearchFoundation, Inc.

DIET OF THE RED-BACKED BUZZARD (BUTEOPOLYOSOMA EXSUL) AND THE SHORT-EAREDOWL (As•roFLAMMEUS SUINOA) IN THE JUAN FERN3.NDEZ ARCHIPELAGO OFF CHILE

MARCELOA. FUENTES,• JAVIER A. SIMONETTI,•'3 M. SOLEDAD SEPOLVEDA 2 AND PATRICIA A. ACEVEDO • •Departamentode CienciasEcoldgicas, Facultad de Ciencias,Universidad de Chile, Casilla653, Santiago,Chile 2Departmentof InfectiousDiseases, University of Florida, Gainesville, Florida 32611 U.S.A.

The Juan FernandezIslands (Robinson Crusoe, Santa eared Owls (seven from Santa Clara Island and 13 from Clara and Alejandro Selkirk) off the Chilean coasthold a RobinsonCrusoe Island, as well as prey remains found unique biota featuring high levels of endemismin both scatteredaround a nest). Prey remainswere identifiedto plantsand terrestrialanimals (Castilia 1987, Stuessyet the finest possiblelevel of resolution. Identification of al. 1991). Four raptorsinhabit the islands:Peregrine Fal- mammalian specieswas attained by comparisonwith a con (Falcoperegrinus), American Kestrel or Cern•calode referencecollection in the Secci6nMamiferos, Museo Na- Juan Fernandez(F. sparverius),Red-backed Buzzard or cionalde Historia Natural, Santiago. Blindado(Buteo polyosoma), and Short-earedOwl or Nuco Thirty-six vertebrateprey items were identified from (Asioflammeus). Of these,two are endemicsubspecies: F. pellets of Red-backed Buzzards, as well as seven inver- sparveriusfernandensis and B. polyosomaexsul (Johnson tebrates(three coleopterans, three arachnids, and one decao 1965, Schlatter1987). These speciesare threatenedby pod).Given the proportionof biomasscontributed by ver- dlegalhunting and nestravaging by introducedmammals tebrates,we focusedour analysis on this prey category (CONAF 1976). In general,Chilean raptorsare decreas- (Table 1). The mostfrequent prey were rodents (47.3%), ing due to illegal hunting, habitat alteration,and prey particularly the introducedhouse mouse (Mus musculus), reduction(Jaksifi and Jim•nez 1986). Even the Short- whereasbirds, largely petrels,accounted for 39.8% of the eared Owl is categorizedas inadequatelyknown (Glade vertebrateprey. Interestingly,it has been suggestedthat 1987). In fact,the biologyis poorlyif at all known(Schlat- attacksby Red-backedBuzzards may haveforced petrels ter 1987) for the raptors of Juan Fernandez Islands and to useburrows to reducepredation risks (Johnson 1965). for all oceanic Chilean birds. While this behaviormay decreasetheir vulnerabilityto The dietsof Juan Fernandez'Red-backed Buzzard and buzzards, it is ineffective toward introduced terrestrial Short-earedOwl are casesin point. Althoughthere are predatorssuch as coatis (Nasua nasua) and cats(Felis catus, somedata availableon their respectivediets in continental Torres and Aguayo 1971). Chile (Schlatter et al. 1980, Rau et al. 1992), no such Red-backedBuzzards also preyed on Europeanrabbits, quantitativeinformation exists on their diet in Juan Fer- which accountedfor 5.6% of their vertebrateprey. Un- nandezIslands. Anecdotal information suggests that Red- identifiedfishes made up 5.6% of the prey by number. backedBuzzards prey on introducedrodents (Mus and Housse(1945) mentionedfish remains among the preyof Rattus), poultry, young goats,and native petrels(Pterod- Buteopolyosoma polyosoma, suggesting that they were oc- roma;Lonnberg 1921, Johnson 1965, Torresand Aguayo casionalprey when the abundanceof mammalsand birds 1971). Accordingto S•iz (1982), Red-backedBuzzards do was low. Fish may have been consumedas carrion. In not consumeEuropean rabbits (Oryctolaguscuniculus). fact, Buteopolyosoma exsul was observedby one of us Short-caredOwls, on the other hand,reportedly prey on (MSS) scavengingon deadfur seal(Arctocephalus philip- Mus and Rattus and rabbits (CONAF 1976, Sfiiz 1982). pii) pupsand eating placentae of Juan Fernandezfur seals, Herein, we describequantitatively the dietsof islandRed- a suspectedbut sofar unconfirmedbehavior of this raptor backed Buzzards and Short-cared Owls. (Torres 1987). Three pelletscontained some hair attrib- From November1988 to April 1991 and in January utableto seals.Scavenging suggests that Red-backedBuz- 1992, we collected26 pelletsregurgitated by Red-backed zard is an opportunisticraptor. Buzzards(22 from AlejandroSelkirk Island and four from In centralChile, B. polyosomapolyosoma preys largely RobinsonCrusoe Island), and 20 pelletscast by Short- on native rodents,secondarily on introducedrabbits, and less frequently on native birds (Schlatter et al. 1980). Therefore,this hawk'sdiet in the Juan FernfindezIslands is roughlysimilar to that in the continent,except for the 3 To whom all correspondenceshould be sent. consumptionof fish and large mammal carrion.

167 168 SHORTCOMMUNICATIONS VOL. 27, NO. 3

Table 1. Percentof prey in the diet of Red-backedBuz- changesin their resourcespectrum (see Crespo 1966, Dal- zard (Buteopolyosoma exsul) and Short-earedOwl (Asio by 1975). Therefore, if faced with a declinein the abun- flammeussuinda) in the Juan FernfindezArchipelago. dance of exotic speciesby their control or eradication, raptorsmay turn to nativebirds which alreadyare threat- PREY CATEGORIES B UTEO ASIO ened.Alternatively, raptors may respondnumerically, with a populationreduction coupled to the declineof their staple Mammals prey, which also representsa problem given the fragile House mouse (Mus musculus) 41.7 0.0 conservationstatus of these raptors. This paradoxical Europeanrabbit (Oryctolagus situation should be consideredwhen planning for the cuniculus) 5.6 60.7 controlof introducedrabbits and rats, a mandatoryaction Rodentia: unidentified 5.6 10.7 if the survivalof severalunique speciesof the Juan Fer- Mammal: unidentified 2.6 10.7 nfindez Islands are to be saved from extinction.

Birds RESUMEN.--En baseal anfilisisde regurgitados,estudia- Pterodroma 27.8 17.9 mosla dieta del Aguiluchode Mfis Afuera (Buteopolyo- Birds: unidentified 11.1 0.0 somaexsul) y del Nuco (Asioflammeussuinda) en el Ar- Fishes chipiglagode Juan Fernfindez.E1 aguiluchoconsume Fish: unidentified 5.6 0.0 principalmentemfiridos (introducidos) y aves.En menor medidadepreda sobre conejos, consumiendo ademfis peces Total prey 36 28 y mamiferosmarinos como carrofia. E1 nuco consume prin- cipalmenteconejos, fardelas y mfiridos.En ambasrapaces destacaque la mitad de su dieta la componenespecies ex6ticas. A total of 28 prey items,all vertebrates,were determined for Short-earedOwl (Table 1). The most frequent were ACKNOWLEDGMENTS European rabbits, both adults and juveniles (eight and We are indebtedto M. Ricci and Corporaci6nNacional nine individuals, respectively).Secondarily, Short-eared Forestal (CONAF) personnelfor their hospitalityand Owls preyed on birds, particularly both adults and eggs field assistance,and to F.M. Jaksi(: for commentsto the of petrels,as well as on unidentifiedrodents. In continental manuscript. Chile, Short-eared Owls consume rodents almost exclu- LITERATURE CITED sively,mostly native species,and a negligiblenumber of invertebrates(Rau et al. 1992). ACEVEDO,P.V. 1990. Efecto de Oryctolaguscuniculus Despite our small sample,it is noteworthythat in the sobre la regeneraci6nde Chenopodiumcrusoeanum, Juan Fernfindez Islands both Red-backed Buzzards and Myrceugeniafernandeziana y Sophorafernandeziana Short-earedOwls preyedlargely on introducedmammals: Tesis, Medicina Veterinaria, Universidadde Concep- 53% by number in the Red-backedBuzzard and 71% in ci6n, Chillfin, Chile. the Short-earedOwl. The stapleprey appearedto be rab- CASTILLA,J.C. (ED.). 1987. Islas ocefinicaschilenas: bits and murid rodents,species which are threateningthe conocimientocientifico y necesidadesde investigaci6n. survival of severalnative specieson the islands.The Eu- EdicionesUniv. Cat61icade Chile, Santiago,Chile. ropean rabbit, for instance,precludes the recruitment of CONAF. 1976. Plan de Manejo del Parque Nacional seedlingsof endangerednative shrubs,such as Chenopo~ Juan Fernfindez.Doc. T&. Trabajo22, Santiago,Chile dium crusoeanum.Acevedo (1990) stated that an effective CRES?O,J.A. 1966. Ecologlade una comunidadde roe- recoveryplan for the flora of Juan Fernfindez ought to dotes silvestresen el partido de Rojas, provinciade considerthe eradicationor a severepopulation reduction BuenosAires. Rev.Mus. Argent.Cienc. Nat. Bernardino of rabbits.Rabbit eradication,however, will depressthe Rivadavia, Ecol. 1:79-134. prey base for the Short-eared Owl. On the other hand, DALBY,P.L. 1975. Biologyof Pamparodents: Balcarce muridsaffect the survivalof severalground-nesting birds, area, Argentina. Publ. Mus., Michigan State Univ, including petrels regarded as vulnerable (Glade 1987, Biol. Set. 5:149-272. Rottmanand L6pez-Callejas1992) by preyingupon their GLADE,A.A. (ED.). 1987. Libro Rojode losVertebrados eggs.As with rabbit control,controlling those exotic ro- Terrestres de Chile. Corporaci6n Nacional Forestal, dentsin order to ensurethe survival of somebird species Santiago, Chile. may havethe secondaryeffect of diminishingthe resource HOUSSE,R. 1945. Las aves de Chile en su clasificaci6n base for raptors whose conservationis also of concern. moderna,su vida y suscostumbres. Ediciones Univ. de Chilean raptorstend to be opportunisticpredators, con- Chile, Santiago,Chile. centrating on the most abundant and vulnerable prey JAKSI•,F.M. ANDJ.E. JIMI•NEZ. 1986. The conserva- available (see Jaksi6 and Simonetti 1987 for a review), tion statusof raptorsin Chile. Birdsof Prey Bulletin 3: exhibiting both functional and numerical responsesto 95-104. SEPTEMBER 1993 SHORT COMMUNICATIONS 169

-- ANDJ.A. SIMONETTI.1987. Predator/preyre- SCHLATTER,R.P. 1987. Conocimientoy situaci6nde la lationshipsamong terrestrial vertebrates: an exhaustive ornitofaunaen las islasoceanicas chilenas. Pages 271- review of studies conducted in southern South America. 285 in J.C. Castilia (ED.), Islas oceanicaschilenas: Rev. Chil. Hist. Nat. 60:221-244. conocimientocientifico y necesidadesde investigaci6n JOHNSON,A.W. 1965. The birdsof Chile and adjacent EdicionesUniv. Cat61icade Chile, Santiago,Chile. regionsof Argentina, Bolivia and Peril. Vol. 1. Platt --, J.L. YAiqlEZAND F.M. JAKSIIS. 1980. Food- EstablecimientosGrfificos, BuenosAires, Argentina. niche relationshipsbetween Chilean Eagles and Red- LONNBERG,E. 1921. The birds of Juan FernfindezIs- backed Buzzards in central Chile. Auk 97:897-898 land and Easter Islands. Pages19-24 in C. Skottsberg STUESSY,T.F., C. MARTICORENA,R. RODRIGUEZ,D.J. (ED.), The Natural History of Juan Fernfindez and CRAWFORD AND O.M. SILVA. 1991. Endemism in the Easter Island. Vol. III. Almquist & Wiksells, Uppsala, vascularflora of the Juan FernandezIslands. Aliso 13' Sweden. 297-307. RAU, J.R., M.C. VILLAGRA, M.L. MORA, D.R. MAR- TORRES, D. 1987. Antecedentes sobre el lobo fino de TiNEZ AND M.S. TELLERdA. 1992. Food habits of the Juan FernandezArctocephalus philippii y proyecciones Short-eared Owl (Asiofiammeus) in southern South para su estudio.Pages 287-317 in J.C. Castilia (ED.), America. J. Raptor Res. 26:35-36. Islasoceanicas chilehas: conocimiento cientifico y ne- ROTTMANN,J. AND M.V. L(SPEZ-CALLEJAS.1992. Es- cesidadesde investigaci6n.FdicJones Univ. Cat61icade trategia nacional de conservaci6nde aves. Servicio Chile, Santiago,Chile. Agrlcola y Ganadero, Divisi6n de Protecci6nde los TORRES,D. AND A. AGUAYO. 1971. Algunas observa- Recursos Naturales Renovables, Ser. Tdc. 1:1-16. cionessobre la fauna del Archipiglagode Juan Fer- S3,IZ, F. 1982. Proposici6n de un m•todo de control nandez. Bol. Univ. Chile 12:26-37. integradodel conejoen el Archipi•lago de Juan Fer- nfindez. Univ. Cat61ica de Valparaiso, Valparaiso, Chile. Received8 February 1993; accepted1 June 1993

J Raptor Res. 27(3):169-171 ¸ 1993 The Raptor ResearchFoundation, Inc.

OBSERVATIONSOF WINTERING GYRFALCONS(FALCO RUSTICOLUS) HUNTING SAGEGROUSE (CENTROCERCUS UROPHASIANUS) IN WYOMING AND MONTANA U.S.A.

CHRISTOPHER S. GARBER WyomingNatural DiversityDatabase, The Nature Conservancy, 3165 UniversityStation, Laramie, WY 82071 U.S.A.

BRIAN D. MUTCH The PeregrineFund, Inc., 5666 WestFlying Hawk Lane,Boise, ID 83709 U.S.A.

STEPHEN PLATT WyomingDepartment of EnvironmentalQuality, 250 Lincoln St., Lander, WY 82520 U.S.A.

Little has beenwritten on the prey preferencesof win- preyingupon this species.However, captive Gyrfalcons tering Gyrfalcons(Falco rusticolus) outside of their breed- flownin falconryare reported to beable to kill SageGrouse ing range (Palmer 1988, Dobler 1989, Sanchez 1993). (Christopherand Hardaswick1988). Most summariesof Gyrfalconprey selectionare from data Between 8 November and 6 December 1992, CSG and collectedduring the breedingseason (Sherrod 1978). Al- SP observedan individualGyrfalcon on 10 separatedays though wintering Gyrfalconsoccur within the range of (identificationwas basedon comparisonsof photographs) Sage Grouse (Centrocercusurophasianus; Cade 1982, 14 km eastof Lander,Wyoming. The Gyrfalconappeared Johnsgard1983), we found no reportsof wild Gyrfalcons to be an adult female basedon its plumage, yellow feet,