This is a great example of this bird. To follow up on what Kelly said, here is some text from the Audubon website..."The Brown-headed Cowbird (Molothrus ater) is North America's most notorious brood parasite. Instead of building their own nests, incubating their own eggs and raising their own nestlings, Brown-headed Cowbirds have a different breeding strategy. Cowbird females use other bird species as hosts -- laying their eggs in the nests of other bird species and relying on these hosts to incubate and raise their chicks. Scientists have now recorded that Brown-headed Cowbirds have parasitized over 220 host species, ranging from the Black-capped Vireo and Wood Thrush to the Blue-winged Teal and Red-headed Woodpecker. While not all hosts make good foster parents -- a number of species reject cowbird eggs -- cowbird chicks have been successfully reared by over 150 host species, with songbirds comprising the majority of hosts."
