Bronzed Cowbird (Molothrus aeneus)

Bronzed Cowbird

[order] PASSERIFORMES | [family] Icteridae | [latin] Molothrus aeneus | [UK] Bronzed Cowbird | [FR] Vacher bronze | [DE] Rotaugen-Kuhstarling | [ES] Tordo ojirojo | [NL] Roodoogkoevogel


Genus Species subspecies Breeding Range Breeding Range 2 Non Breeding Range
Molothrus aeneus NA, MA sw USA to Panama
Molothrus aeneus aeneus
Molothrus aeneus assimilis
Molothrus aeneus loyei

Physical charateristics

Male: Larger than Brown-headed Cowbird; does not have a brown head. Bill longer. Red eye can be seen only at close range. In breeding season, a conspicuous ruff
on the nape. Female: Smaller, with a smaller ruff; dull blackish, much like male, not gray like female Brown-headed Cowbird.

Listen to the sound of Bronzed Cowbird

[audio: Cowbird.mp3]

Copyright remark: Most sounds derived from xeno-canto

wingspan min.: 30 cm wingspan max.: 36 cm
size min.: 18 cm size max.: 22 cm
incubation min.: 13 days incubation max.: 14 days
fledging min.: 0 days fledging max.: 0 days
broods: 35   eggs min.: 35  
      eggs max.: 40  


North America, Middle America : Southwest USA to Panama


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.


A brood parasite, never raising its own young. In courtship display on ground, male pu
ffs 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 promiscu
Nest: Builds no nest; lays eggs in nests of other birds.
Eggs: Pale blue-green, unmarked. Number of eggs laid per female unknown, but may be nearly one egg per day for several weeks. When laying eggs, female cowbird may pierce eggs already in nest. Fre
quent “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 habits

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.
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.


This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Bronzed Cowbird status Least Concern


Southwestern United States to western Panama. Summers in extreme southeastern California, central and southern Arizona, southwestern New Mexico, southern Texas (north to Eagle Pass). Winters in southern Arizona (rarely), southern Texas.
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.

Distribution map

Bronzed Cowbird distribution range map

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