LYME, CT Red-eyed Vireo (Vireo olivaceus) with chicks at nest, including a Brown-headed Cowbird (Molothrus ater) chick. Brown-headed Cowbirds engage in a form of nest or brood parasitism, laying their eggs in other birds' nests, and allowing the host bids to raise the cowbird chicks. Cowbird chicks often grow larger and faster than the other chicks, as in this case, and outcompete the nesting birds own chicks.