Use of Communal Roosts and Foraging Areas by Bald Eagles Wintering in the Klamath Basin

Abstract

Patterns of use of 5 communal roosts and 3 feeding areas by bald eagles (Haliaeetus leucocephalus) in the Klamath Basin of southern Oregon and northern California were investigated during the winters of 1978-79 and 1979-80. Bald eagles arrived in late October and were most abundant during late January. Counts peaked at approximately 500 eagles, which constitutes one of the largest wintering concentrations in the lower 48 states. Numbers declined from February through March. There were several major shifts in use of roosts and feeding areas within and between years, which depended on the location of an accessible food supply (mainly waterfowl), which in turn was affected by weather, season, and human activities. Comparisons in bald eagle behavior are made between several locations, and common aspects are described. J. WILDL. MANAGE. 51(2):415-420 Winter concentrations of bald eagles usually occur in areas of high food availability from the southern Alaskan coast to central California, from Montana to Texas, and along the Mississippi River and its tributaries. Bald eagles are opportunistic foragers, and their foraging behavior and habitat use vary considerably. Foods during winter include carrion and live prey consisting of several species of fish, waterfowl, and even small mammals (Hancock 1964, Swisher 1964, Lish 1973, McClelland 1973, Servheen 1975, Stalmaster 1976, Steenhof 1976, Griffin 1978, Keister 1981, Frenzel 1985). Bald eagles often change prey and foraging areas during the winter and sometimes fly long distances to different wintering areas (Young 1983, Lingle and Krapu 1986, Isaacs and Anthony 1987). The proximity of communal roosts to feeding areas varies considerably; distances range from 0.25 km along rivers (Hansen et al. 1980) to 24.0 km in basins (Edwards 1969). Type of roosting habitat also varies from relatively small deciduous trees (Steenhof 1976) to large coniferous trees (Hansen et al. 1980, Keister and Anthony 1983). Successful management of wintering populations of bald eagles requires an understanding of the reasons for variability in foraging behavior and habitat use. The purpose of this paper is to describe the concurrent use of communal roosts and foraging areas by bald eagles and to identify factors that influence variable use of these areas. This study was conducted under the auspices of the Oreg. Coop. Wildl. Res. Unit; Oregon State Univ., Oreg. Dep. Fish and Wildl. (ODFW), U.S. Fish and Wildl. Serv. (USFWS), and the Wildl. Manage. Inst. cooperating. The USFWS and the Nat. Conserv. funded the study under Contract 14-16-009-79018. This is Oregon State Univ. Agric. Exp. Stn. Tech. Pap. 7579. We thank D. C. Sasse, R. R. Opp, R. A. Ingram, J. V. Towman, J. L. Hainline, R. C. Fields, and J. F. Wegener as well as others at Lava Beds Natl. Monument (LBNM), Modoc and Klamath Natl. For., ODFW, Klamath Basin Natl. Wildl. Refuge, and U.S. Bur. Land Manage. for help with coordinated roost counts. Living accomodations were provided by ODFW, and the hospitality shown by J. F. Wegener at LBNM was greatly appreciated. J. A. Crawford, D. Faulkenberry, F. B. Isaacs, and K. Steenhof reviewed earlier drafts of the manuscript.