WARMING WINTERS AND CHANGING HABITATS: INTERACTIVE EFFECTS ON RAPTOR POPULATIONS AND IMPLICATIONS FOR CONSERVATION By

Studies of multiple taxa across broad-scales suggest that species distributions are shifting poleward in response to global climate change. Understanding the influence of distribution shifts on regional population indices will be an important part of interpreting population trends within local management units because, compared to a time when distribution were less dynamic, changes in population indices may be less likely to reflect local environmental conditions. I examined the latitudinal center of abundance for the winter distributions of six western North America raptor species using Christmas Bird Counts from 1975-2011. I predicted that birds wintered further north during warmer winters and that winter raptor distributions have shifted north over time. Also, I considered whether population indices within North American Bird Conservation Regions (BCR) were explained by distribution shifts. All six wintering raptors shifted their distributions north over time and five of six raptor species tended to winter further north during warmer winters. Northward shifts explained 44% of regional population trends emphasizing the importance of understanding how distribution shifts and population indices interact on a regional scale. Raptors may be particularly responsive to warming winters because of flexible migration behavior, high intraspecific competition for nesting sites that drives males to winter farther north, or both. If population-level