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1 October 2012 Changes in the Annual Cycle of North American Raptors Associated with Recent Shifts in Migration Timing
Josh Van Buskirk
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Recent changes in the timing of spring migration associated with climate change are occurring in hundreds of species of Northern Hemisphere birds. Much less is known about effects on autumn migration, especially for birds of prey. I studied simultaneous changes in spring and autumn phenology using data from 14 raptor species at two bird observatories on the shore of Lake Superior, North America. Median migration date advanced by 0.13 days·year-1 in spring and was delayed by 0.23 days·year-1 in autumn, with significant heterogeneity among species. Long-distance migrants were observed late in spring and early in autumn and showed less phenological change during autumn than short-distance migrants. The migratory period has become more extended, especially for short-distance migrants. Opposite responses during the two seasons had the effect of extending time spent to the north of the study area, by up to 30 days in some species since the early 1970s. These phenological shifts—potentially related to climate change— are causing dramatic changes in the annual cycle of North American raptors; whether these are beneficial or detrimental is unknown.

© 2012 by The American Ornithologists' Union. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
Josh Van Buskirk "Changes in the Annual Cycle of North American Raptors Associated with Recent Shifts in Migration Timing," The Auk 129(4), 691-698, (1 October 2012).
Received: 1 April 2012; Accepted: 1 August 2012; Published: 1 October 2012

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