A Yellow Warbler nest containing one Brown-headed Cowbird egg. Photo by Stylurus via Birdshare. A Yellow Warbler nest containing one Brown-headed Cowbird egg. Photo by Stylurus via Birdshare.
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If you are in the U.S. or Canada, there is a good chance you’ve discovered a nest with Brown-headed Cowbird eggs in it. Cowbirds don’t build their own nest; instead they lay their eggs in other birds’ nests and their chicks are raised by the host species—a behavior known as brood parasitism. This can be detrimental to the host bird, but like other native birds, cowbirds and their eggs are protected by the Migratory Bird Treaty Act and it is illegal to disturb them. Read more about this interesting species in our online bird guide.

Cornell Lab of Ornithology

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