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Photo © Al Tuttle

What are brood parasites?

Brood parasites are birds that lay eggs in other species’ nests.

North America’s most common brood parasite is the Brown-headed Cowbird (Shiny Cowbird and Bronzed Cowbird occur in localized areas of the southernmost United States and Caribbean). These native birds lay their eggs in the nests of other birds, who then incubate their eggs and raise the cowbirds as their own. Brown-headed Cowbird females can lay as many as 36 eggs in a season. Over 140 different species of birds are known to have raised young cowbirds. Host parents often accept the cowbird egg, but different species react in different ways. Some destroy the egg by pecking or removing it, others build a new layer over the bottom of the original nest to restart their nesting process, and some expel the cowbird nestlings from the nest.

It’s important to note that Brown-headed Cowbirds are native to North America and therefore protected under federal law, meaning that their eggs should not be removed from nests unless the monitor holds special federal permits (some states have programs in place to protect endangered species). You can learn more about Brown-headed Cowbirds here.

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Cornell Lab of Ornithology

Cornell Lab of Ornithology