Are Those Cowbirds in the Nest?
The Brown-headed Cowbird is a North American brood parasite, meaning that it lays its eggs in the nests of other species, making no nest of its own. Reporting cowbird activity is important for understanding nesting success among a wide variety of “host” species (species that accept cowbird eggs). How can you recognize cowbird parasitism in nests you’re monitoring?
In our detailed post, you can learn about the basics of Brown-headed Cowbird natural history, then read about the six signs that a cowbird may have parasitized a nest. You’ll also find photos to help you identify eggs and nestlings of cowbirds. Common species that NestWatchers report as parasitized include Eastern Phoebe, Northern Cardinal, House Finch, American Robin, and, occasionally, box-nesting species.
Cowbirds are a native species and incapable of reproducing without a host. We have tips for discouraging cowbirds, but the single best thing you can do as a NestWatcher is to not visit a nest if you see or hear cowbirds in the area. Wait until another time to check the nest to avoid alerting the cowbird to its presence. If you do find cowbirds in a nest you’re monitoring, we ask that you leave them be and report their presence to NestWatch.