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Providing evidence to improve practice

Individual study: Effects of trapping of brown-headed cowbirds Molothrus ater on the nesting success of song sparrows Melospiza melodia at three sites in the Fraser River Delta, British Columbia, Canada

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


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Remove/control adult brood parasites Bird Conservation

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%).