Brown-headed Cowbird

Brown-headed Cowbird

Molothrus ater

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.

Interesting Information

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.

Description

Adult Description

Size: 17-22 cm (7-9 in)
Wingspan: 28-36 cm (11-14 in)
Weight: 38-50 g (1.34-1.77 ounces)
Medium-sized songbird.
Medium-long tail.
Bill stout and pointed.
Male shiny black with brown head and neck.
Female dull gray-brown.
Eyes black.
Wings rather long and pointed.
Legs black.

Sex Differences

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

Male

Body, wings, and tail shiny black. Head, nape, and chest dull dark brown. Bill black. Legs black.

Female

Entirely grayish brown. Chest with dull streaks. Throat whitish. Suggestion of faint pale eyestripe. Bill gray.

Immature

Juvenile similar to female, but more distinctly streaked below. Males molting in fall may be patched black and brown.

Photo taken from: The Sibley Field Guide by David Allen Sibley

Habitat

Breeds in areas with grassland and low or scattered trees, such as woodland edges, brushy thickets, fields, prairies, pastures, orchards, and residential areas.

Behavior

Forages on ground, often in association with cows or horses. Outside of breeding season, forages in large flocks with other blackbirds.

Food

Seeds and arthropods.

Taxonomy

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Aves
Order:	Passeriformes
Family:	Icteridae
Genus:	Molothrus
Species:	Molothrus ater
Subspecies:	Molothrus ater artemisiae
	Molothrus ater ater
	Molothrus ater obscurus

Similar Species

Bronzed Cowbird is larger, has longer bill, larger head, shorter tail, and red eyes. Male lacks brown hood.
Shiny Cowbird male is entirely glossy black, but female is extremely similar to female Brown-headed Cowbird, except bill is slightly longer.
Brewer's Blackbird female darker brown, has dark around the eyes, and has a thinner, more pointed bill.
Female and juvenile Brown-headed Cowbird resemble sparrows, but are larger, completely dull gray-brown, and have unstreaked backs.

Bird 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."

Eggs look like this

Photo taken from: ARCTOS Collaborative Collection Management Solution

Videos

Brown-headed Cowbird

Up close and personal

	Sources Used To Construct This Page
	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. 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. 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.

	All photos and videos © Rick Swartzentrover - Free for non-profit use.