When warblers warn of cowbirds, blackbirds get the message

This is the story of three bird species and how they interact. The brown-headed cowbird plays the role of outlaw: It lays its eggs in other birds' nests and lets them raise its young—often at the expense of the host's nestlings. To combat this threat, yellow warblers have developed a special "seet" call that means, "Look out! Cowbird!"

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