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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society SUMMARY(1) Diets of three nesting raptor species were evaluated from 5939 prey items collected from nests in south-western Idaho during a 10-year period that included a complete jack rabbit population cycle and an unusual ground squirrel population crash.(2) Jack rabbits were the principal prey of golden eagles; Townsend's ground squirrels were the main prey of prairie falcons and red-tailed hawks. Prairie falcons had the most specialized diets, and red-tailed hawks the most diverse. None of the three raptor diets reflected the relative abundance of prey types in the environment.(3) Diet diversity of each of the three raptor species expanded as the abundance of their main prey declined. Ground squirrels and birds were alternate prey for eagles; gopher snakes, kangaroo rats, and r4bbits were alternate prey for red-tailed hawks. Prairie falcons had no single important alternate prey species.(4) Yearly frequencies of main prey in each of the three raptor diets were correlated with the annual abundance of that prey in the environment. Frequencies of alternate prey were correlated not with their own abundance but inversely with the abundance of the principal prey.(5) Eagle preference for jack rabbits was strong and unaffected by changes in prey densities. Red-tailed hawk selectivity for jack rabbits was inversely related to ground squirrel abundance, suggesting 'switching' behaviour. Prairie falcon selectivity for ground squirrels did not vary with ground squirrel densities.(6) Prey choice was generally consistent with predictions of the original optimal diet model, but red-tailed hawk prey selection appeared to depend on relative prey densities. Degree of diet specialization and plasticity are probably related to a raptor's life-history characteristics, and may influence a raptor's effects on its prey populations.

SAS INSTITUTE INC. 1987. SAS/Stat guide for personal computers. Version 6 ed. SAS Inst. Inc., Cary, N.C. 1029pp. STAHLECKER, D. W. 1975. Effect of a new transmission line on wintering prairie raptors. Condor 80:444-446. 1979. Raptor use of nest boxes and platforms on transmission towers. Wildl. Soc. Bull. 7:59-62. STALMASTER, M. V. 1980. Salmon carrion as a winter food source for red-tailed hawks. Murrelet 61:43-44. WILLIAMS, R. D., AND E. W. COLSON. 1989. Raptor associations with linear rights-of-way. Pages 173-192 in B. G. Pendleton, proj. ed. Proc. western raptor management symposium and workshop. Natl. Wildl. Fed.,

The Arctic is entering a new ecological state, with alarming consequences for humanity. Animal-borne sensors offer a window into these changes. Although substantial animal tracking data from the Arctic and subarctic exist, most are difficult to discover and access. Here, we present the new Arctic Animal Movement Archive (AAMA), a growing collection of more than 200 standardized terrestrial and marine animal tracking studies from 1991 to the present. The AAMA supports public data discovery, preserves fundamental baseline data for the future, and facilitates efficient, collaborative data analysis. With AAMA-based case studies, we document climatic influences on the migration phenology of eagles, geographic differences in the adaptive response of caribou reproductive phenology to climate change, and species-specific changes in terrestrial mammal movement rates in response to increasing temperature.

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