COWBIRD

any of six or seven species of birds belonging to the family Icteridae (order Passeriformes) that are parasitic egg-layers. Cowbirds forage on the ground, and derive their name from their habit of associating with cattle in order to prey on insects stirred up from vegetation. In most species the male cowbird is uniform glossy black in colour, while the female is grayish brown. Like some cuckoos, cowbirds habitually lay their eggs in the nests of other birds. Young cowbirds, usually one to the host nest, customarily either displace competing nestlings or appropriate their food and may even exceed the foster parents in size. Some species parasitize many kinds of birds, but others use the nests of only one or two kinds of orioles. The best-known species is the brown-headed cowbird (Molothrus ater) of temperate North America. The bay-winged cowbird (M. badius) of South America is the only species that builds its own nest.