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Molothrus ater1.jpg
Female brown-headed cowbird
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Icteridae
Genus: Molothrus
Swainson, 1832

Cowbirds are birds belonging to the genus Molothrus in the family Icteridae. They are of New World origin. They are brood parasites, laying their eggs in the nests of other species.

The genus was introduced by the English naturalist William John Swainson in 1832 with the brown-headed cowbird (Molothrus ater) as the type species.[1][2] The genus name combines the Ancient Greek mōlos meaning "struggle" or "battle" with thrōskō meaning "to sire" or "to impregnate".[3]

The genus contains six species:[4]

Image Scientific name Common Name Distribution
Screaming Cowbird (Molothrus rufoaxillaris).jpg Molothrus rufoaxillaris Screaming cowbird north east and central Argentina, south east Bolivia, central Brazil and throughout Paraguay and Uruguay
Giant Cowbird - Pantanal - Brazil H8O0545 (23593619780).jpg Molothrus oryzivorus (formerly in Scaphidura) Giant cowbird southern Mexico south to northern Argentina, and on Trinidad and Tobago
Bronzed Cowbird (Molothrus aeneus) (7223072934).jpg Molothrus aeneus Bronzed cowbird southern U.S. states of California, Arizona, New Mexico, Texas, and Louisiana south through Central America to Panama
Shiny cowbird (Molothrus bonariensis) male.JPG Molothrus bonariensis Shiny cowbird South America
Molothrus ater 2.jpg Molothrus ater Brown-headed cowbird Southwestern Canada, United States and Mexico

The non-brood parasitic baywing was formerly placed in this genus; it is now classified as Agelaioides badius.


Cowbirds eat insects, including the large numbers that may be stirred up by cattle.

The birds in this genus are infamous for 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 female cowbird may continue to observe the nest after laying eggs. If the cowbird egg is removed, the female cowbird may destroy the host's eggs to dissuade further removals, according to the Mafia hypothesis. Widespread predatory behaviors in cowbirds could slow the evolution of rejection behaviors and further threaten populations of some of the >100 species of regular cowbird hosts.[5]


  1. ^ Swainson, William John; Richardson, J. (1831). Fauna boreali-americana, or, The zoology of the northern parts of British America. Part 2. The Birds. London: J. Murray. p. 277. The title page bears the year 1831 but the volume did not appear until 1832.
  2. ^ Paynter, Raymond A. Jr, ed. (1968). Check-list of Birds of the World. Volume 14. Cambridge, Massachusetts: Museum of Comparative Zoology. p. 195.
  3. ^ Jobling, James A. (2010). The Helm Dictionary of Scientific Bird Names. London: Christopher Helm. p. 258. ISBN 978-1-4081-2501-4.
  4. ^ Gill, Frank; Donsker, David, eds. (2019). "Oropendolas, orioles, blackbirds". IOC World Bird List Version 9.2. International Ornithologists' Union. Retrieved 2 September 2019.
  5. ^ Jeffrey P. Hoover; Scott K. Robinson (13 March 2007). "Retaliatory mafia behavior by a parasitic cowbird favors host acceptance of parasitic eggs". Proceedings of the National Academy of Sciences. Retrieved 26 August 2009.

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