The post-fledging period represents a time of considerable energetic constraint and selection pressure for juvenile songbirds. Despite its potential importance for survival, this period remains one of the least studied stages of the annual cycle. Using radio telemetry and taking advantage of unique topographical characteristics at three spatially separated study sites, we assessed four hypotheses regarding the function of broad-scale, landscape-level movements for juveniles: (1) commencement of migration, (2) habitat optimization, (3) selection of a breeding territory, and (4) formation of a homing target. For the Blackpoll Warbler (D. striata), we found that movement was directed to the southeast at all three study sites but individuals were also associated with river valleys, providing support for the homing-target and habitat-optimization hypotheses. For the Yellow-rumped Warbler (Dendroica coronata), we found that movement was directed toward and down river valleys, following the unique orientation of the valleys at each study site, supporting the habitat-optimization hypothesis. Our results provide important insights into the function of broad-scale landscape-level movements for juvenile songbirds prior to migration, as well as their relative importance to individuals' success, both immediate and future.
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Vol. 112 • No. 4