Despite recent increases in the number of demographic studies of birds in urban environments, the postfledging period remains poorly understood. Because novel ecological factors, including changes in predator abundance and invasive exotic shrubs, are associated with urbanization, we asked (1) how does postfledging survivorship vary across a rural-to-urban landscape gradient and (2) to what extent does Amur Honeysuckle (Lonicera maackii), an invasive exotic shrub, influence patterns of survivorship and habitat selection? During the 2008 and 2009 breeding seasons, we placed radiotransmitters on fledgling Northern Cardinals (Cardinalis cardinalis; n = 45) and Acadian Flycatchers (Empidonax virescens; n = 31) that occupied riparian forest stands embedded within a rural-to-urban landscape gradient in central Ohio, USA. Predation was the primary cause of fledgling mortality for both species, but cumulative survivorship (± SE) for Acadian Flycatchers (0.720 ± 0.097; 22 days) was 1.6 × that of Northern Cardinals (0.440 ± 0.077; 71 days). Survivorship across the entire postfledging period was not associated with urbanization, but during the initial 3 days after fledging, when mortality rates were highest, Northern Cardinal survivorship was positively related to urbanization. Northern Cardinals strongly selected for complex understory vegetation that was positively associated with survivorship, but survival was not related specifically to cover by Amur Honeysuckle. Contrary to assumptions that postfledging survival declines as landscapes urbanize, our results suggest that urban forests may provide suitable habitat for juvenile birds living within metropolitan areas.
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Vol. 128 • No. 2