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30 June 2016 Potential effects of Brown-headed Cowbirds (Molothrus ater) on host postfledging dispersal and survival
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Nest parasitism by Brown-headed Cowbirds (Molothrus ater) negatively affects nest production and nest success of the majority of their hosts. However, it is unclear what effects cowbird fledglings have on host broods during the postfledging period. We monitored 65 nests of Ovenbirds (Seiurus aurocapilla) from 2012–2014 in central Missouri, 49% of which were parasitized by Brown-headed Cowbirds. We used radio-telemetry to track daily movements, survival, and parental care for 13 Ovenbird fledglings from parasitized nests that fledged cowbirds and 21 Ovenbird fledglings from non-parasitized nests. Clutch size and nest productivity were lower in parasitized nests, but mean nestling mass at fledging and total brood size (host and parasite young) did not differ between parasitized and non-parasitized nests. All mortalities occurred within the first 10 days after fledging. Estimated postfledging cumulative survival and observed adult care were similar between parasitism groups. There was no difference in movement patterns of Ovenbirds during the first 2 weeks postfledging; however, Ovenbirds from non-parasitized nests moved farther from the nest after 14 days compared to Ovenbirds from nests that fledged a cowbird. Our observations do not support the hypothesis that negative effects of nest parasitism by Brown-headed Cowbirds extend into the postfledging period for Ovenbirds.

© 2016 The Wilson Ornithological Society
Julianna M. A. Jenkins and John Faaborg "Potential effects of Brown-headed Cowbirds (Molothrus ater) on host postfledging dispersal and survival," The Wilson Journal of Ornithology 128(2), 404-411, (30 June 2016).
Received: 18 March 2015; Accepted: 1 October 2015; Published: 30 June 2016

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