How do brown-headed cowbirds (Molothrus ater) cause nest failures in song sparrows (Melospiza melodia)? A removal experiment

Published source details Smith J.N.M., Taitt M.J., Zanette L. & Myers-Smith I.H. (2003) How do brown-headed cowbirds (Molothrus ater) cause nest failures in song sparrows (Melospiza melodia)? A removal experiment. The Auk, 120, 772-783.
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This study is summarised as evidence for the following.

	Action	Category
	Remove/control adult brood parasites Action Link

Remove/control adult brood parasites

A replicated, controlled study in 1995-9 at three riparian sites in British Columbia, Canada (Smith et al. 2003), found that the success rates of song sparrow Melospiza melodia nests were higher at sites where female brown-headed cowbirds Molothrus ater were removed (51 in 1996, 163 in 1997 at one site; 24 in 1998 at another) than in a control site with no cowbirds removed, both across all years (44% success for 296 nests in removal sites vs. 32% success for 615 in control sites) and just in years when cowbirds were removed (44% success for 296 nests in removal sites vs. 34% success for 399 in control sites). Nest survival rates were higher for song sparrow eggs in removal sites (96.5% daily survival vs. 94.7%), but there was no significant difference in nestling survival (97.4% daily survival vs. 96.6%). Significantly fewer nests were abandoned after being parasitised by cowbirds in removal sites than control sites (9% abandoned vs. 16.5%).