SHEEP CARCASS AVAILABILITY AND USE BY BALD EAGLES

摘要

We studied sheep carcass availability and use by Bald Eagle (Haliaeetus leucocephalus) in the Willamette Valley, Oregon, during winter 1990. We determined availability of sheep carcasses every 2-4 days along a 65-km transect. Bald Eagle numbers were counted weekly at five communal roosts. Counts ranged from 13 to 49; immatures consistently outnumbered adults. We calculated persistence rates of 137 sheep carcasses; those < 200 m from a road or house were rarely used by eagles and persisted longer than carcasses farther away. Eagles were feeding on sheep carcasses in 83% of feeding observations along the transect, and 87% of 234 Bald Eagle castings contained wool. However, we found no evidence of eagle predation on sheep. Availability of sheep carcasses appears to be a primary factor influencing eagle use of the valley in winter. Our estimate of available sheep carrion/ day was more than sufficient to meet the needs of the eagles wintering in the valley. However, if eagle numbers continue to increase or if carrion becomes less available, eagles may leave the valley. We recommend that ranchers make carcasses available to eagles away from sources of human disturbance, rather than burying them as is currently practiced.