Abstract
Abstract We studied the effects of brood parasitism by Brown-headed Cowbirds (Molothrus ater) and other factors on food provisioning rates of Swainson's Warblers (Limnothlypis swainsonii), a secretive and poorly understood species of conservation concern. We used time-lapse video systems to collect provisioning data at 25 nests, nine of which were parasitized by Brown-headed Cowbirds. We found strong relationships between feeding rate and brood size with increases from 2.0 feeding visits/hr for nests with a single Swainson's Warbler nestling to 3.0/hr for broods of four. We also found an effect of nestling age with 1.9 visits/hr early and 3.2 visits/hr late in the nestling period. The relationships between cowbird parasitism and provisioning were complex. Nests with brood size of one or three that contained a single cowbird nestling had greater provisioning rates (2.5 and 3.3 visits/hr, respectively) than non-parasitized nests (2.0 and 2.6 visits/hr, respectively). Nests with two cowbirds and no Swainson'...
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