First Record of a Brown-headed Cowbird Parasitizing an Ash-throated Flycatcher Nest

Abstract

The Brown-headed Cowbird (Molothrus ater) is a common brood parasite whose range has undergone a major expansion into western North America. We describe an apparent first report of an Brown-headed Cowbird parasitizing an Ash-throated Flycatcher (Myiarchus cinerascens) nest. Although Brown-headed Cowbirds are unlikely to parasitize most cavity-nesting species, cavities with larger entrances are at a higher risk. Host choice significantly affects Brown-headed Cowbird breeding success, and the Ash-throated Flycatcher is unlikely to be an important host. We also report briefly on Western Bluebirds (Sialia mexicana) laying eggs opportunistically in Ash-throated Flycatcher nests.