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Providing evidence to improve practice

Individual study: The effects of trapping brown-headed cowbirds Molothrus ater on the nesting success of California gnatcatchers Polioptila californica in western Riverside County, California, USA

Published source details

Braden G.T., McKernan R.L. & Powell S.M. (1997) Effects of nest parasitism by the brown-headed cowbird on nesting success of the California gnatcatcher. The Condor, 99, 858-865


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 before-and-after study at four coastal scrub sites in California, USA (Braden et al. 1997), found that levels of parasitism of California gnatcatcher Polioptila californica nests (initiated after 5th May) by brown-headed cowbirds Molothrus ater was significantly lower in 1994-5, following the removal of a total of 507 cowbirds over the two years, compared to in 1992-3 (10% of 132 nests parasitized in 1994-5 vs. 46% of 107 nests in 1992-3). However, nest success over the whole breeding season was no higher in years with cowbird control (21.7% of nests successful in 1994-5 vs. 11.2% in 1992-3).