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Museo DamasoAn- tonio Larrafiaga, No. 5-Serie de Divulgaci6n. Monte- in sympatricharriers (Circus)in western Europe. Ger- video, Uruguay. faut 63:17-120. MARTI,C.D. 1987. Raptor food habits studies.Pages 67- W1TKOWS}tI,J. 1989. Breeding biology and ecologyof the 80 in B.A. Giron Pendleton, B.A. Millsap, K.W. Cline, Marsh Harrier Circusaeruginosus in the Barycz Valley, Poland. Acta Ornithol. 25:223-320. and D.M. Bird lEDS.], Raptor management tech- niques manual. Nat. Wildl. Fed., Washington, DC U.S.A. Received 6June 1999; 21 March 2000 J RaptorRes'. 34(3):241-243 ¸ 2000 The Raptor ResearchFoundation, Inc. ABUNDANCEOF THE OGASAWARABUZZAI• ON CHICHIJIMA, THE PACIFICOCEAN TADASHI SUZUKI AND YUKA KATO Departmentof BiologicalScience, Tokyo Metropolitan University, Minami-ohsawa 1-1, Hachi-ohji, Tokyo192-0397, Japan KEYWORDS: Ogasawarabuzzard; Buteo buteo toyoshimai; and its longer beak and shorter wings and tarsi (Momi- Bonin; endemic,density. yama 1927). The Ogasawarabuzzard is listed as an endangeredspe- cies in Japan (Japan Environmental Agency 1998) be- The Ogasawarabuzzard (Buteobuteo toyoshimai) is an cause the population is so small. It is known to inhabit insular subspeciesof the Common Buzzard (B. buteo,Or- the two island groups of the Ogasawaras,Chichijima-ret- nithologicalSociety of Japan 1974, Brazil 1991, Monroe to, and Hahajima-retto (Brazil 1991), with total areas of and Sibley 1993). It is endemic to the Ogasawara(Bonin) 38.2 km9 and 27.0 km2, respectively(Ogasawara Natural Islands, which lie about 1000 km south of Tokyo in the Environmental Group 1992). Among the islands,Chich- Pacific Ocean. It usually nests on rocky cliffs (Funatsu ijima is the largestand probablysupports the largestpop- and Chiba 1991), although tree nestinghas been recently ulation of buzzards.It is also the most developedof the reported (Takagi and Ueda 1998, Kato and Suzuki1999). Ogasawara Islands with a human population of about It differs from a nearest subspecies,B. buteojaponicus,be- 1900 in 1998. In the early 1990s,the number of pairs of causeof its drab plumage with lessbrown on the uppers Ogasawarabuzzards on Chichijima was estimated to be 242 SHORT COMMUNICATIONS VOL. 34, NO. 3 about 15 (Higuchi et al. 1988, Funatsu and Chiba 1991) oughly. Therefore, it is unlikely that the population of but no recent estimatesof the present population have buzzards on the island has increased in recent decades. been made. Here, we present the resultsof a studywe We estimatedthe densityof the buzzardpopulation on undertook to estimatethe number of pairs currentlyon Chichijima to be approximately1.2 pairs per km9. Our Chichijima. densityestimate was rather high compared to densities of other breeding populations of Common Buzzards. STUDY AREA Densitiesup to 0.78 pairsper km9 havebeen reportedin Chichijima is situatedat 27ø04'Nand 142ø13'Eand is wooded areas of middle Europe (Newton et al. 1982) but approximately24 kma in area. Terrain on the islandis normally densitiesare <0.5 pairsper km9 (Newton 1979, steep with many mountain areas of volcanic origin but Newton et al. 1982, Dare and Barry 1990, Davisand Davis elevationsdo not exceed 326 m. There are many rocky 1992, Halley 1993,Jedrejewski et al. 1994, Penteriani and coastal and mountain cliffs that provide potential nest sitesfor Ogasawarabuzzards. Chichijima is generallycov- Faivre1997). Factorslimiting raptor population are food ered with low vegetationand canopy trees consistingof supply,nest-site availability, and human intrusion (New- native and introduced speciesdo not exceed 15 m in ton 1991). No other raptors, excluding occasionalvisi- height (Shimizuand Tabata1991). About 73% of Chich- tors, inhabit Chichijima; therefore, the high densityof ijima is covered with regenerated native forests and Ogasawarabuzzards on Chichijima may be due to the scrubs,and the remaining27% includescoastal forests, abundance of nest sitesand the lack of competition from exotic low shrubs (Leuca•na leucocephala)and grasses other raptors for food. It may also be due to the overall (Stachytarphetajamaic•nsis),cultivated fields, crags, and vil- lage areas. absenceof human persecution. The densityof buzzardsalso appearsto be high on METHODS other islandsin Chichijima-rettoand Hahajima-retto,al- We systematicallysearched Chichijima for Ogasawara though recent surveydata are not available(Higuchi et buzzardsin March, April, May,June, August,and Decem- al. 1988, Funatsu and Chiba 1991, Suzuki 1991). We es- ber 1998 and February, March, April, and May 1999 (1- timated the total population of Ogasawarabuzzards on 2 wk per mo) during which time at leastone of us stayed the OgasawaraIslands to be only about 85 pairs using on Chichijima. When buzzardswere found, we recorded our densityestimate of 1.2 pairs per km9 on Ogasawara their numbers, spatialposition, flight path, any socialin- and a total areaof potentialhabitat of 70.7km 9 including teractions,and other patternsof behavior.Whenever pos- Mukojima-retto, the third island group of the Ogasawar- sible,buzzards were individuallyidentified usingplumage characteristics,plumage deficits or differing stagesof as. Further study is needed to better document the total plumagedevelopment. When necessary,we searchedpre- population of Ogasawarabuzzards, including nonterri- sumed territories to determine occupancy.In so doing, torial individuals,and to determine its nestingecology to we consideredtwo nonantagonisticadults inhabiting a insure the future conservationof the subspecies. putative territory to be a pair. RESULTS AND DISCUSSION RESUMEN.--Buteotrttteo toyoshimai es endfmico alas Islas Ogasawara (Bonin), a 1000 km al sur de Japtn. Invesu- We found a total of 28 territorial pairs and one un- gamosel nfimero de parejasde Buteobuteo toyoshimai en mated, territorial individual by March 1999 and recon- Chichijima (ca. 24 km2), la isla m/rsgrande de las Oga- firmed their occupancyof territories in May 1999. The sawara,en 1998-99. Veintiocho parejasfueron encontra- pairs were dispersedrather evenlyin both native and in- das. Este estimativofue el doble que el previamente re- troduced habitats.For 16 of the 28 pairs, breeding activ- portado, probablementedebido a la bfisquedaminuciosa ity was confirmed either by observingdeliveries of nest- hecha en la isla. La densidadde parejas(1.2 parejaspor ing materialsto nests,adults attending nests, incubating km'•) fue m/rs alta en comparacitn con los valoresde adults,nestlings in nests,or fledglingsin their territories. Buteobuteo reportados en otras partes del mundo. For the remaining eight pairs,neither attended nestsnor [Traduccitn de Ctsar Marquez] fledglings were found; nevertheless,we suspectedthat they bred becausewe observedthem either delivering ACKNOWLEDGMENTS prey to presumed nests,repeatedly visiting and leaving We thank T. ¾asui, E Nobushima, and H. Chiba for the same locations (probably nesting sites) on cliffs, or helpful information and field support,and S. Katada,N. they showed aggressiveor alert behavior when we en- Hasebe, T. Kubota, and Y. Kamimura for field assistance. tered their territoriesduring the breeding season. We are grateful to S. Nohara and N. Kachi for providing Our estimate of 28 pairs of Ogasawarabuzzards on us with the opportunity to conduct this study,and alsoto Chichijima was nearly twice that previouslyreported for reviewers of JRR for improving the manuscript. This the island (Suzuki 1982, Higuchi et al. 1988, Funatsuand studywas partially supportedby the ResearchProject on Chiba 1991). However, a comparison of our data with ConservationMethods of SubtropicalIsland