Brown-headed CowbirdMolothrus ater

adult male
Rick and Nora Bowers/VIREO
adult female
Rick and Nora Bowers/VIREO
juvenile
Rick and Nora Bowers/VIREO
adult male
Rob & Ann Simpson/VIREO
nest with 3 Veery eggs and 1 cowbird egg
Michael Patrikeev/VIREO

Description

Centuries ago this bird probably followed bison herds on the Great Plains, feeding on insects flushed from the grass by the grazers. Today it follows cattle, and occurs abundantly from coast to coast. Its spread has represented bad news for other songbirds: Cowbirds lay their eggs in nests of other birds. Heavy parasitism by cowbirds has pushed some species to the status of "endangered" and has probably hurt populations of some others.

Habitat

Farms, fields, prairies, wood edges, river groves. Favors open or semi-open country at all seasons. In winter often concentrates in farmland, pastures, or cattle feedlots, where foraging is easy. More widespread in breeding season, in grassland, brushy country, forest edges, even desert, but tends to avoid dense unbroken forest.

Feeding Diet

Mostly seeds and insects. Seeds (including those of grasses, weeds, and waste grain) make up about half of diet in summer and more than 90% in winter. Rest of diet is mostly insects, especially grasshoppers, beetles, and caterpillars, plus many others, also spiders and millipedes.

Feeding Behavior

Forages mostly by walking on the ground. Often associates with cattle or horses in pastures, catching the insects flushed from the grass by the grazing animals. Originally, was closely associated with bison herds on the Great Plains.

Nesting

A brood parasite, its eggs and young being cared for by other bird species. In breeding season, male displays by fluffing up body feathers, partly spreading wings and tail, and bowing deeply while singing. Groups of males sometimes perch together, singing and displaying. Nest: No nest built; eggs laid in nests of other birds. Eggs: Whitish with brown and gray spots concentrated at larger end. Female may lay nearly one egg per day for several weeks, up to 40 in a season, exceptionally 70 or more. Female often removes an egg from "host" nest before laying one of her own. Known to have laid eggs in nests of over 220 species of birds, and over 140 of those are known to have raised young cowbirds. Young: Fed by "host" parents. Develop rapidly, and leave nest usually after 10-11 days.

Eggs

Whitish with brown and gray spots concentrated at larger end. Female may lay nearly one egg per day for several weeks, up to 40 in a season, exceptionally 70 or more. Female often removes an egg from "host" nest before laying one of her own. Known to have laid eggs in nests of over 220 species of birds, and over 140 of those are known to have raised young cowbirds. Young: Fed by "host" parents. Develop rapidly, and leave nest usually after 10-11 days.

Young

Fed by "host" parents. Develop rapidly, and leave nest usually after 10-11 days.

Conservation

Undoubtedly far more abundant and widespread today than it was originally, and having a negative impact on other species. Surveys suggest slight declines in total numbers in recent decades.

Range

Present all year in many southern areas. Very widespread in nesting season, localized at other times. May begin to depart from nesting areas by August or even July.

Listen

whistle call variants
whistles, chatter, and flight
male song
female chatter
male song and whistle call
male songs & female chatter (duets)

Similar Species

adult, breeding

European Starling

Often regarded as a pest, the Starling wins our grudging admiration for its adaptability, toughness, and seeming intelligence. Brought to North America in 1890, it has spread to occupy most of the continent, and is now abundant in many areas. Sociable at most seasons, Starlings may gather in immense flocks in fall and winter. When the flocks break up for the breeding season, males reveal a skill for mimicry, interrupting their wheezing and sputtering songs with perfect imitations of other birds.

adult male, breeding

Rusty Blackbird

Birders might say that this blackbird is rusty because it spends so much time in the water. In migration and winter it is usually in swampy places, wading in very shallow water at the edges of wooded streams. In summer it retires to northern spruce bogs; no other blackbird has such a northerly breeding distribution. The name "Rusty" applies to the colors of fall birds, but it could also describe the rusty-hinge sound of the creaking song.

adult male

Brewer's Blackbird

This is the common blackbird of open country in the West, often seen walking on the ground with short forward jerks of its head. It adapts well to habitats altered by humans, and in places it may walk about on suburban sidewalks or scavenge for crumbs around beachfront restaurants. In winter, Brewer's Blackbirds gather in large flocks, often with other blackbirds, and may be seen foraging in farmland all across the western and southern states.

adult male, Eastern

Bronzed Cowbird

Larger than the Brown-headed Cowbird and mostly restricted to the Southwest, this species is another brood parasite. It may be more specialized in its choice of "hosts," and is thought to have seriously affected populations of some species, such as Hooded Orioles in southern Texas. The Bronzed Cowbird has expanded its range in our area during the last century; in Arizona, where it is now common, it was unrecorded before 1909.

adult male

Shiny Cowbird

Originally native to South America, this little blackbird spread gradually through the West Indies in recent decades, island-hopping north through the Lesser Antilles and then west toward Cuba. It arrived in Florida in 1985, and has become locally common there, with some seen elsewhere in the Southeast. Like other cowbirds, this species is a parasite, so its arrival in our area was not welcomed by conservationists.

adult male

Boat-tailed Grackle

Until the 1970s, this big blackbird was considered to be the same species as the Great-tailed Grackle, but the two forms overlap on the coasts of Texas and Louisiana without interbreeding. The Boat-tail is a more aquatic creature, nesting in marshes, scavenging on beaches. Except in Florida, it is seldom found far away from tidewater. Boat-tailed Grackles nest in noisy colonies, the males displaying conspicuously with much wing-fluttering and harsh repeated calls.

adult male

Great-tailed Grackle

Wherever it occurs, this big blackbird is impossible to overlook -- especially the male, with his great oversized tail and incredible variety of callnotes. In the southwest, flocks of Great-tailed Grackles feed in open country during the day, but often come into towns at night, forming noisy roosting aggregations in the trees in city parks. During recent decades, this species has greatly expanded its range within our area, and it is still spreading north in some areas.

adult male Coastal (Purple)

Common Grackle

Throughout the east and midwest, this big blackbird is a very familiar species on suburban lawns, striding about with deliberate steps as it searches for insects. Common Grackles often nest in small colonies, and several males may perch in adjacent treetops to sing their creaking, grating songs. Big flocks are often seen flying overhead in the evening, heading for major communal roosts, especially from late summer through winter.

Vireo

iPad Promo