Brown-headed Cowbird

Brown-headed Cowbird, adult male

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Brown-headed Cowbird, adult female

Brown-headed Cowbird, juvenile

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1. Description
2. Sound
3. Conservation Status
4. Other Names
5. Cool Facts
6. Full detailed species account

The Brown-headed Cowbird is the only brood parasite common across North America. A female cowbird makes no nest of her own, but instead lays her eggs in the nests of other bird species, who then raise the young cowbirds.

Description

• Medium-sized songbird.
• Medium-long tail.
• Bill stout and pointed.
• Male shiny black with brown head and neck.
• Female dull gray-brown.

• Size: 17-22 cm (7-9 in)
• Wingspan: 28-36 cm (11-14 in)
• Weight: 38-50 g (1.34-1.77 ounces)

Sex Differences

Male shiny black with brown head and neck, female plain gray-brown.

Sound

Song a pair of low "glug, glug" notes followed by slurred whistles ending on a very high pitch. Calls include a chatter and a whistled "fee-bee."

Conservation Status

Originally a bison-following bird of the Great Plains, the Brown-headed Cowbird spread eastward in the 1800s as forests were cleared. It is a common bird across most of North America, but numbers are declining in most areas. Its habit of nest parasitism can cause the decline of species with small populations, such as Kirtland's Warbler and Black-capped Vireo. You can help scientists learn more about this species by participating in the Celebrate Urban Birds! project.

Other Names

Vacher à tête brune (French)
Tordo negro (Spanish)

Cool Facts

• The Brown-headed Cowbird is the only brood parasite common across North America. A female cowbird makes no nest of her own, but instead lays her eggs in the nests of other bird species, who then raise the young cowbirds.
• The Brown-headed Cowbird lays eggs in the nests of many different species of birds. Recent genetic analyses have shown that some female cowbirds will use a number of different hosts, but most females specialize on one particular host species.
• Social relationships are difficult to figure out in birds that do not build nests, but male and female Brown-headed Cowbirds are not monogamous. Genetic analyses show that males and females have several different mates within a single season.

Sources used to construct this page:

1. Lowther, P. E. 1993. Brown-headed Cowbird (Molothrus ater). In The Birds of North America, No. 47 (A. Poole, and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C. 
2. Woolfenden, B. E., Gibbs, H. L., and Sealy, S. G. 2002. High opportunity for sexual selection in both sexes of an obligate brood parasitic bird, the brown headed cowbird (Molothrus ater). Behavioral Ecology and Sociobiology 52: 417 425.
3. Woolfenden, B. E., Gibbs, H. L, Sealy, S. G, and McMaster, D. G. 2003. Host use and fecundity of individual female brown-headed cowbirds. Animal Behaviour 66: 95-106.