Shiny CowbirdMolothrus bonariensis

adult male
Tom J. Ulrich/VIREO
adult female
Steve Mlodinow/VIREO

Description

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.

Habitat

Semi-open country. In North America, has been found mostly near the coast, often foraging on extensive lawns. In the tropics, found in any kind of open or semi-open terrain, mostly in the lowlands.

Feeding Diet

Mostly seeds and insects. Diet in North America has not been studied. In the tropics, feeds on insects and other arthropods, and many seeds.

Feeding Behavior

Forages mostly by walking on the ground in open areas. Often forages in small flocks, and may associate with other kinds of cowbirds or other blackbirds. In the tropics, will feed in association with horses or cattle in pastures.

Nesting

A brood parasite, never raising its own young. Early in breeding season, males sing to attract females. A male singing to a female on the ground may take off and fly in a wide circle around her with fluttering wingbeats. Nest: Builds no nest of its own; lays its eggs in nests of other birds. Eggs: Quite variable in color: may be unmarked white, or may have gray dots, large red spots, dark lines, brown blotches, or rarely can be all dark red. Number of eggs laid by a female in one season is unknown, but may be many. Female sometimes punctures eggs already in a nest before she lays her own. In South America, parasitizes nests of many species. May specialize in other areas: in Puerto Rico, mostly parasitizes Yellow-shouldered Blackbird. Young: Cowbird nestling is fed by "host" parents and develops rapidly, probably leaving nest after about 10-12 days.

Eggs

Quite variable in color: may be unmarked white, or may have gray dots, large red spots, dark lines, brown blotches, or rarely can be all dark red. Number of eggs laid by a female in one season is unknown, but may be many. Female sometimes punctures eggs already in a nest before she lays her own. In South America, parasitizes nests of many species. May specialize in other areas: in Puerto Rico, mostly parasitizes Yellow-shouldered Blackbird. Young: Cowbird nestling is fed by "host" parents and develops rapidly, probably leaving nest after about 10-12 days.

Young

Cowbird nestling is fed by "host" parents and develops rapidly, probably leaving nest after about 10-12 days.

Conservation

Impact of this parasite on North American birds remains to be seen. In Puerto Rico, has driven Yellow-shouldered Blackbird to endangered status.

Range

Pattern of migration within North America still poorly known. In some recent years, numbers have been seen moving through southern Florida in spring, suggesting flocks arriving from Caribbean. Strays have dispersed as far as Texas, Oklahoma, and Maine.

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

Brown-headed Cowbird

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.

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.

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