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1 March 2011 Reproductive Status of the Shiny Cowbird in North America
William Post, Paul W. Sykes
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We collected 17 (13 females, 4 males) Shiny Cowbirds (Molothrus bonariensis) during the passerine nesting season in July 1999 and 2003 in Jasper County, southwestern South Carolina. Five females (38%) were laying eggs, as ascertained from the condition of their reproductive organs. Two females collected on 1 July 1999 and 19 July 2003 had eggs in their oviducts, and would have deposited eggs within 1 day. Shiny Cowbirds have been in North America for at least 24 years, but only males had been collected before this study. Most of those collected had enlarged testes, as did the four collected in the present study, but these data are not proof that breeding actually occurred. The reproductive condition of the females we collected provides material evidence that the species breeds in North America. It is not known which species are being parasitized by Shiny Cowbirds, but several species widespread in the southeastern United States are highly suitable hosts.

William Post and Paul W. Sykes "Reproductive Status of the Shiny Cowbird in North America," The Wilson Journal of Ornithology 123(1), 151-154, (1 March 2011).
Received: 23 August 2010; Accepted: 1 November 2010; Published: 1 March 2011
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