In an urban landscape, population viability may require successful movement of recently fledged birds between habitat patches, yet postfledging movements are rarely studied. We used radiotelemetry to track 26 American Robin (Turdus migratorius), 15 Swainson's Thrush (Catharus ustulatus), 46 Spotted Towhee (Pipilo maculatus), and 35 Song Sparrow (Melospiza melodia) fledglings across the urban gradient of the Seattle metropolis, to document the relative use of specific features of the built and forested environment and to correlate land-cover metrics with survival during the postfledging period. Survival of postfledging birds, other than American Robins, was high, and the effects of land cover on survival were limited. Across species, we observed lower survival in forested areas than in the suburban lands around them, but this may have been a function of fledgling age. Once juvenile birds became independent, they often moved into suburbs without increased risk of death. We found little consistency in relative habitat use within species, with the exception of American Robins, which used suburban residential areas more than forested areas. However, resource use by the other species was context-specific: (1) use of residential areas by Song Sparrows was highest where this habitat was least common, (2) use of forested areas by Spotted Towhees decreased with increasing level of urbanization, and (3) use of heavy-medium urban areas by Swainson's Thrush decreased with increasing abundance of roads.
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Vol. 126 • No. 2