The Brown-headed Cowbird (Molothrus ater) is a well-known obligate brood parasite that spread northward into California’s Sacramento Valley in the 1930s, supported by anthropogenic changes to the landscape. Many species of western birds now serve as hosts for Brown-headed Cowbirds and brood parasitism has contributed to the decline of several passerines in California. Parasitism of Eastern Phoebe (Sayornis phoebe) and Say’s Phoebe (S. saya) is well documented, but it is unreported in Black Phoebe (S. nigricans). Here we report the first confirmed nest parasitism of Black Phoebe by Brown-headed Cowbird. While monitoring Black Phoebe nests in Glenn County, California, we documented 4 instances of Brown-headed Cowbirds parasitizing active Black Phoebe nests. Brown-headed Cowbird nestlings likely fledged in 2 of the instances, 1 nest fell to the ground, and the fourth was likely depredated. In 1 successful nest, the Black Phoebe parents fledged 1 of their own young, along with the parasitic nestling. Based on our study, and the lack of detection in earlier studies, the current rate of Brown-headed Cowbird parasitism of Black Phoebes remains low, and we perceive no immediate conservation concern. However, further research and monitoring is needed to determine if parasitism is an increasing trend that could impact Black Phoebe productivity.

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