Influence of summer biogeography on wood warbler stopover abundance

We evaluated the effect of summer biogeography of migrant wood warblers (Pa rulidae) on their stopover abundance. To characterize abundance patterns, w e used mist-net capture data from spring and fall migration in the Middle R io Grande Valley, New Mexico, spring migration on the Gulf Coast Of Louisia na, and fall migration on the Gulf Coast of Alabama. To describe the summer biogeography of 47 species of wood warblers, we used indices of their summ er range size, their summer density, and distance between their summer rang es and our netting sites. Multiple linear regressions indicated that biogeo graphic indices explained 55% and 49% of variation in captures in the Middl e Rio Grande Valley during spring and fall, respectively. On the Gulf Coast these regressions explained 25% of the variation during spring at the Loui siana site and 51% during fall at the Alabama site. Both summer range size and distance between the summer range and study sites explained significant portions of the variation in three of the four analyses. Interestingly, th e importance of biogeographic factors was least evident among spring migran ts along the Gulf Coast of Louisiana. The difference between this site and other sites may reflect differences between migrants arriving after a Gulf crossing and those migrating across continental land masses or possibly an increased importance of winter biogeography for migrants crossing the Gulf of Mexico in the spring. In general, these results indicate that abundance of migrant warblers at our netting sites in both the eastern and western Un ited States during spring and fall migration were influenced by summer biog eography. Consequently, we suggest including biogeographic analyses in asse ssments of conservation priorities for local stopover sites.