P0876-P0879.Pdf
876 SHORT COMMUNICATIONS od, temperature and diet quality. Physiol. Zool. Calow [eds.], Physiologicalecology: an evolution- 66537-560. ary approach to resourceuse. Blackwell, Oxford. NOVOA, F. F. 1993. Ecofisiologiade Zonotrichia ca- STEEL, R. G. D., ANDJ. H. TORRIE. 1985. Bioestad- pensis:cambios estacionalesen el gasto y la ad- istica: principios y procedimientos.McGraw-Hill, quisici6n de energia. Ph.D. diss., Universidad Bogota. Chile, Santiago. WALSBERG, G. E., AND C. W. THOMPSON. 1990. An- SIBLEY, R. M. 1981. Strategiesin digestionand defe- nual changesin gizzard size and function in a fru- cation, p. 109-139. In C. R. Townsend and P. givorous bird. Condor 92~794-795. The Condor 98:876-879 0 The CooperOrnithological Society 1996 WINTERING SWAINSONS’ HAWKS IN CALIFORNIAS’ SACRAMENTO-SAN JOAQUIN RIVER DELTA ’ SEBASTIANK. HERXKY Department of Wildlife, Fish, and ConservationBiology, Universityof California at Davis, Davis, CA 95616 Key words: Swainsons’ Hawk; Buteo swainsoni; served foraging flocks of up to 16 Swainson’s Hawks natural history; winter distribution;Sacramento-San on five Delta islands previna on small rodents in close JoaquinRiver Delta. associationwith farming operations. The objective of the present study was to systematically monitor the The Swainson’s Hawk (Buteoswainsoni) is considered population to determine wintering seasonchronology, a summer resident breeder on lame Darts of North size, composition, distribution, and foraging ecology. America, leaving in winter to migrate south to South STUDY AREA AND METHODS America (AOU 1983, Palmer 1988). Wintering Swain- son’s Hawks in North America had been confirmed The study area was in the Sacramento-SanJoaauin only from southernFlorida, where somejuveniles were River Delta in the Central ValIey ofCalifornia (38005’N, found during most winters, and from the southwestern 121”35’w) (Fia.
[Show full text]