Bronzed Cowbird
Bronzed Cowbird
Molothrus aeneus
At a Glance
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.
All bird guide text and rangemaps adapted from by Kenn Kaufman漏 1996, used by permission of Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Category
Blackbirds and Orioles, Perching Birds
IUCN Status
Least Concern
Habitat
Arroyos and Canyons, Desert and Arid Habitats, Fields, Meadows, and Grasslands, Landfills and Dumps, Shrublands, Savannas, and Thickets
Region
California, Florida, Southeast, Southwest, Texas
Behavior
Direct Flight, Flitter
Population
6.600.000
Range & Identification
Migration & Range Maps
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.
Description
8 1/2" (22 cm). Heavier than Brown-headed Cowbird, with longer bill, shorter tail, red eyes (hard to see). Neck ruff gives look of hunched shoulders. Females dull black (Texas) or gray-brown (Arizona).
Size
About the size of a Robin
Color
Black, Brown, Red
Wing Shape
Rounded
Tail Shape
Rounded, Square-tipped
Songs and Calls
Wheezy and guttural whistling notes and various squeaks and squeals.
Call Pattern
Rising
Call Type
Hi, Whistle
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.
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Behavior
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.
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.
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.
Conservation
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.
Climate Threats Facing the Bronzed Cowbird
Choose a temperature scenario below to see which threats will affect this species as warming increases. The same climate change-driven threats that put birds at risk will affect other wildlife and people, too.