EASTERN BLUEBIRDS EJECT BROWN-HEADED COWBIRD EGGS

The relationship between the Brown-headed Cowbird (Molothrus ater) and its cavity-nesting hosts has received little attention because of the assumption that cowbirds rarely parasitize these hosts. We tested the Eastern Bluebird (Sialia sialis), a host that is sometimes heavily parasitized by cowbird...

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Bibliographic Details
Published in:The Condor (Los Angeles, Calif.) Calif.), 2006-08, Vol.108 (3), p.741-745
Main Authors: Peer, Brian D, Hawkins, Lyndon R, Steinke, Edwin P, Bollinger, Patricia Blair, Bollinger, Eric K
Format: Article
Language:English
Subjects:
Animal reproduction
Birds
brood parasitism
Brown-headed Cowbird
Eastern Bluebird
egg rejection
Eggs
Molothrus
Molothrus ater
Ornithology
SHORT COMMUNICATIONS
Sialia sialis
Sialis
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Summary:The relationship between the Brown-headed Cowbird (Molothrus ater) and its cavity-nesting hosts has received little attention because of the assumption that cowbirds rarely parasitize these hosts. We tested the Eastern Bluebird (Sialia sialis), a host that is sometimes heavily parasitized by cowbirds, for egg ejection behavior. Bluebirds ejected 65% of experimentally added cowbird eggs (n  =  20), but ejected no experimentally added conspecific eggs (n  =  66). This suggests that cowbird parasitism, not conspecific brood parasitism, is the selective pressure responsible for egg ejection in this species. This level of rejection may be conservative because bluebirds nest in dark cavities, which may make cowbird eggs difficult to detect by bluebirds.
ISSN:0010-5422
1938-5129
2732-4621
DOI:10.1650/0010-5422(2006)108[741:EBEBCE]2.0.CO;2