Home, near and far.
Breeds across most of the contiguous United States and southern Canada, extending into Mexico. They are year-round residents in many southern regions and along the Pacific Coast.
Birds Heard
FIELD GUIDE
FIELD GUIDE
New World Blackbirds, Troupials, and Allies
Brown-headed Cowbird
Molothrus ater
The Brown-headed Cowbird is a widespread North American blackbird known for its unique reproductive strategy of brood parasitism. Females lay their eggs in the nests of other bird species, relying on the host parents to raise their young. This behavior, coupled with their adaptability to human-altered landscapes, has allowed them to expand their range significantly.
Migratory/ResidentSmall BlackbirdVaried CallsOmnivorous
- Length
- 15-22 cm
- Wingspan
- 32-38 cm
- Weight
- 32-50 g
Typical adult measurements.
Individuals and populations vary.
01 / The telltale details
You’ll know it
when you see it.
Start with shape and behavior. Then look for the smaller details.
- 01
Adult Male
Glossy black body with a contrasting rich brown head; appears all black in poor light.
- 02
Adult Female
Plain dusty brown overall, lighter on the head and underparts, with faint streaking on the belly.
- 03
Juvenile
Streaked plumage, generally lighter gray than the adult female.
- 04
Bill Shape
Short, thick, and conical, distinguishing it from other blackbirds.
02 / A place in the world
Where life
takes it.
Favors open or semi-open country, including fields, meadows, pastures, forest edges, and suburban areas. They often associate with livestock and avoid dense, unbroken forests.
Stay a while. Or follow the season.
Northern populations are migratory, moving to the southern United States and Mexico for winter, typically arriving in breeding areas by late March or April. Southern populations are often permanent residents.
03 / Listen a little closer
A voice
of its own.
Produces a variety of clicks, whistles, and chatter-like calls, along with a distinctive gurgling song.
04 / The life behind the feathers
A day in its world.
On the menu.
Their diet consists of a variety of seeds and grains, as well as insects, particularly those disturbed by grazing animals.
Brown-headed Cowbirds primarily forage on the ground, often in mixed-species flocks with other blackbirds and starlings, frequently near grazing animals.
A place to begin.
An obligate brood parasite, the female lays her eggs in the nests of over 220 other bird species, never building her own nest or raising her young.
The little routines.
Males display for mates on open ground. Females actively search for host nests, sometimes removing host eggs before laying their own. They may join large roosts with other blackbirds in winter.
One more reason to pay attention
A familiar face.
A few surprises.
Female Brown-headed Cowbirds can lay up to 30-40 eggs in a single breeding season, often one egg per day in different host nests.
Cowbird chicks typically hatch sooner and grow faster than host chicks, often outcompeting them for food.
The species' range expanded significantly with European settlement and the introduction of livestock, as they adapted from following bison to cattle.
05 / An eye for the difference
Could it be
someone else?
Bronzed Cowbird
Molothrus aeneusBronzed Cowbirds are stockier with a heavier bill and lack the distinct brown head of the male Brown-headed Cowbird.
Shiny Cowbird
Molothrus bonariensisShiny Cowbirds have a longer tail and more rounded wings compared to the Brown-headed Cowbird.
Common Grackle
Quiscalus quisculaCommon Grackles are larger with longer tails and a more pointed bill than the Brown-headed Cowbird.
Behind these field notesResearch & references · 12 sources
AI-assisted species research. Prepared September 2026. Details can vary across regions and populations.