Both the Brown-headed Cowbirds and Bronzed Cowbirds are parasitic meaning they lay their eggs in other species nests, Sparrows are a frequent recipient, as are Warblers. Some species are better than others at rejecting them. Yellow Warblers attempt to bury them. Some like Catbirds roll them out. American Redstarts sometimes lose their own nestlings to the bigger more vocal cowbirds. Some nestlings even lean to vocalize like cowbirds in order to get fed. They ave been known to check up on their young, but they will not raise a brood.
