EFFECTS OF BROOD PARASITISM BY BROWN-HEADED COWBIRDS ON WILLOW FLYCATCHER NESTING SUCCESS ALONG THE KERN RIVER, CALIFORNIA

Abstract

Alteration and loss of riparian habitat have played a central role in the decline of riparian bird species (Gaines 1974, Remsen 1978, Laymon et al. 1987). However, the absence of certain species from seemingly suitable habitat (Gaines 1974) suggests that other factors may also be important. In his review of the historical riparian avifauna of the Sacramento Valley, Gaines (1974) suggested that 9 of 12 of the declining species, including the Willow Flycatcher (Empidonax traillii), were susceptible to and had probably been adversely affected by Brown-headed Cowbird (Molothrus ater) brood parasitism.