| Abstract
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The objective of this study was to use physiographic, geographic, and climatic correlates to describe and interpret the breeding and wintering distribution and abundance patterns of Turkey Vultures (Cathartes aura) in the continental United States. Thirty years of data from the National Audubon Society's Christmas Bird Count and the National Biological Survey's Breeding Bird Survey were correlated with remotely sensed and ground sampled environmental data in a raster-based geographic information system. Environmental factors evaluated include elevation, hydrography, thermal reflectance, temperature, precipitation, snow cover, number of frost-free days, vegetation types, and ecoregions, for each 1 Km2 block of the continental United States. A geographic information system overlay process was used to determine statistical relationships between individual and combinations of environmental factors, and sampled vulture data. Vulture numbers were most strongly correlated with geophysical factors, especially a positive relationship with temperature, throughout their range and between seasons. Breeding vultures were most strongly positively correlated with heterogeneous and more open physiographic habitats, such as shrubland, savanna, chaparral, and mixed croplands. Wintering vultures were more strongly correlated with forested areas, presumably for thermal roosting cover. These techniques have helped better determine Turkey Vulture habitat requirements on a scale never before attempted, and can be used for other species in the future.
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