Breeding Biology of Red-winged Blackbirds in the Rocky Mountains, British Columbia

Lee E. Harding

SciWrite Environmental Sciences Ltd., 2339 Sumpter Drive, Coquitlam, British Columbia; e-mail:

Abstract: Weather was the major factor in higher Red-winged Blackbird (Agelaius phoeniceus) productivity (more and larger eggs, lower egg failure rates, higher nestling survival) in 2004 compared to 2005. Nest success varied from 57% to 74%. Causes of mortality included drowning, predation, parental abandonment following predation of nest mates, hypothermia and/or lack of food associated with poor weather, and disease, pneumonia, or other bacterial infections. The diseases included three nestlings with bacterial pneumonia and one with an intestinal streptococcus infection. Two apparently healthy nestlings, when necropsied, had ventricular endocardial necrosis. Despite the adverse weather, this population had higher productivity in both years than provincial averages. This may have been partly due to the absence of predation and competition with Marsh Wrens (Cistothorus palustris), absence of nest site competition with Yellow-headed Blackbirds (Xanthocephalus xanthocephalus), and low levels of Brown-headed Cowbird (Molothrus ater) nest parasitism.

Key words: Red-winged Blackbird, Agelaius phoeniceus, nest success, productivity, nest parasitism, egg temperature

PDFicon Harding, L. 2010. Breeding Biology of Red-winged Blackbirds in the Rocky Mountains, British Columbia. British Columbia Birds 20:16-23.


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