Effects of nest parasitism by the brown-headed cowbird on nesting success of the California gnatcatcher

  • 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 following.

Action Category

Remove/control adult brood parasites

Action Link
Bird Conservation
  1. Remove/control adult brood parasites

    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).


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