Photo: Vince Smith/Flickr Creative Commons

Bronzed Cowbird

Molothrus aeneus

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.
Conservation status Has greatly expanded its range and numbers north of Mexico during 20th century; undoubtedly having a negative impact on its "host" species in some areas.
Family Blackbirds and Orioles
Habitat Farmland, brush, semi-open country, feedlots. Outside the breeding season, generally in very open habitats in the lowlands, foraging in open fields and around cattle feedlots and roosting in brushy woods. In breeding season, wanders widely through many kinds of habitats including forest edge, desert, open woods in mountains.
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.
Photo Gallery
  • adult male, Eastern
  • adult female, Eastern
  • immature, Western
Feeding Behavior

Forages mostly by walking on the ground in the open. May associate with cattle or horses in pastures, catching insects flushed from the grass by the grazing animals. Reportedly may sometimes take ticks or insects from backs of cattle.


Eggs

Pale blue-green, unmarked. Number of eggs laid per female is unknown, but may be nearly one egg per day for up to several weeks. When laying eggs, female cowbird may pierce eggs already in nest. Frequent "hosts" for Bronzed Cowbirds include orioles, thrashers, towhees, many others, including smaller birds like warblers and gnatcatchers. Young: Nestling is fed by the "host" parents and develops rapidly, leaves nest 10-12 days after hatching.


Young

Nestling is fed by the "host" parents and develops rapidly, leaves nest 10-12 days after hatching.

Diet

Seeds and insects. Much of annual diet is seeds, including those of grasses and weeds, and waste grain. Occasionally eats berries. Also eats insects, including caterpillars, beetles, flies, and others, plus snails and spiders. While females are laying eggs, snails may be important as a source of calcium.


Nesting

A brood parasite, never raising its own young. In courtship display on ground, male puffs out his feathers so that he appears almost round, spreads and lowers his tail, and points his bill down as he sings; in more intense version, he vibrates his wings and rises slowly a few feet in air, then slowly descends again. Both sexes are promiscuous, not forming pairs. Nest: Builds no nest; eggs are laid in nests of other birds.

Text © Kenn Kaufman, adapted from
Lives of North American Birds

Illustration © David Allen Sibley.
Learn more about these drawings.

Migration

Only a short-distance migrant, but becomes very uncommon and local in Southwest in winter. Some stray eastward in winter along Gulf Coast, reaching Florida almost regularly.

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Migration

Only a short-distance migrant, but becomes very uncommon and local in Southwest in winter. Some stray eastward in winter along Gulf Coast, reaching Florida almost regularly.

  • All Seasons - Common
  • All Seasons - Uncommon
  • Breeding - Common
  • Breeding - Uncommon
  • Winter - Common
  • Winter - Uncommon
  • Migration - Common
  • Migration - Uncommon
Songs and Calls
Wheezy and guttural whistling notes and various squeaks and squeals.
Audio © Lang Elliott, Bob McGuire, Kevin Colver, Martyn Stewart and others.
Learn more about this sound collection.