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Cowbirds
Female M. ater
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Aves Order: Passeriformes Family: Icteridae Genus: Molothrus Swainson, 1832
Species
M. rufoaxillaris M. oryzivorus M.s aeneus M. bonariensis M. ater

Cowbirds are birds belonging to the genus Molothrus in the family Icteridae. They are brood parasitic New World birds which are unrelated to the Old World cuckoos, one of which, the Common Cuckoo is the best-known brood parasitic bird.

This family includes five species of cowbirds that form the natural genus Molothrus. This has been determined by phylogenetic analyses of mitochondrial DNA sequences (Lanyon 1992, Johnson and Lanyon 1999, Lanyon and Omland 1999, in Lowther, 2004).

The genus Molothrus includes:

• Screaming Cowbird, Molothrus rufoaxillaris
• Giant Cowbird, Molothrus [formerly Scaphidura] oryzivorus
• Bronzed Cowbird, Molothrus aeneus
• Shiny Cowbird, Molothrus bonariensis
• Brown-headed Cowbird, Molothrus ater

It excludes the non-brood parasitic Bay-winged Cowbird Agelaioides [formerly Molothrus] badius.

These birds feed on insects, including the large numbers that may be stirred up by cattle. In order for the birds to remain mobile and stay with the herd, they have adapted by laying their eggs in other birds' nests. The cowbird will watch for when its host lays eggs, and when the nest is left unattended, the female will come in and lay its own eggs.

The cowbird eggs do not look much different from the hosts' eggs, and the host will normally incubate the eggs. The cowbird chicks grow quickly, and may consume most of the food the host brings. If starvation does not kill the other birds, in some species the cowbird will use its large size to push the other chicks out of the nest. The Giant Cowbird does not appear to harm its host oropendola or cacique chicks.

Brown-headed Cowbird, adult male

Brown-headed Cowbird, courtship behavior

• Jaramillo and Burke, New World Blackbirds ISBN 0-7136-4333-1
• The White Laboratory of Animal Behavior, University of Pennsylvania
• Cowbird videos on the Internet Bird Collection