Brown-headed Cowbird

The cowbird gets its name from the habit of following cattle (formerly bison) and catching insects disturbed by the large mammals. Because this bird followed bison herds on their migrations, they are brood parasites. Brood parasites lay their eggs in the nests of other birds. The young cowbirds typically are larger than their nest mates, garner most of the food brought back to the nest by their foster parents and sometimes even push eggs and nest mates from the nest to reduce competition. Some species may recognize the cowbird egg and build a second nest on top of the original nest. Yellow warblers have a tendency to be heavily parasitized by cowbirds, but are also somewhat proficient at identifying the unusual egg in their nest. Some yellow warbler nests have been found in seven layers, each with a cowbird egg in it.