What do they look like?

Brown-headed Cowbirds are small blackbirds with short cone-shaped bills and long, pointed wings. Males appear black with a unique brown head and neck. Females are either dullish gray or brown. Their bills are a dull grey, while their eyes are black. Adult males weigh between 40 and 50 g, and females are about 10% smaller.

Where in the world do they live?

Brown-headed Cowbirds breed from southeastern Alaska, through Canada and the entire continental United States to central Mexico. They winter throughout the southern portions of this range, and also in southern Mexico and the tip of Florida.

What kind of habitat do they need?

Brown-headed Cowbirds prefer habitats with low or scattered trees among grassland vegetation, such as woodland edges, brushy thickets, prairies, fields, pastures, orchards, and residential areas.

How do they reproduce?

Brown-headed Cowbirds lay their eggs in the nests of other birds; female Cowbirds select host nests of another species of bird to lay their eggs in. They wander about, laying eggs in as many nests as they can find and laying up to 40 eggs per season. They lay sequences of 7 eggs, one egg laid in a different nest each day, then rest for several days between egg-laying sequences. The young are then cared for by the host bird. There are 144 different host species documented that raise Brown-headed Cowbird young, so the incubation and parental care of Brown-headed Cowbirds varies greatly depending on the nest in which they are deposited. During the various care processes for Brown-headed Cowbirds, however, they are always fed more often than the young of the host species because they are very active in begging for food from the parents and tend to be bigger than the host species' nestlings. The smallest recorded host of cowbird young is the Brown Creeper, while the largest host is the Meadowlark. Eggs hatch about 9 to 12 days after being laid in the host nest. This is a fairly common length of time for the eggs of the host birds as well. If they survive, they leave the nest in about 8-13 days but continue to be fed by the host parents for between 18 and 35 days. Female Cowbirds are ready to breed when they are 1 year old, but males often take longer. Cowbirds breed between April and June with variation depending on area.

These birds are brood parasites, they lay their eggs in the nests of other birds. These hosts provide all the parental care.

How long do they live?

The oldest known wild Brown-headed Cowbird was 15 years and 10 months old, most do not live nearly as long.

How do they behave?

Brown-headed Cowbirds rarely hop when on the ground, preferring to walk. They are often found in mixed-species flocks with other blackbirds, such as Common Grackles. Brown-headed Cowbirds get their name from their close association with livestock, such as horses and cattle, which disturb insects on the ground when feeding. This allows cowbirds easy access to their food. Because cowbirds have a significant impact on the reproductive success of other species, many other bird species have adapted and can recognize this threat, acting aggressively towards Brown-headed Cowbirds near their nesting territory. Brown-headed Cowbirds are active during the day and migrate short distances between northern breeding areas and more southerly wintering areas.

How do they communicate with each other?

Brown-Headed Cowbirds have a wide variety of calls, such as glug glug glee, bublowcomseee, bub ko lum tseee, glug glug, whssss, pseeee, ch'ch'ch'ch'ch,' kek, kik, and tek. They tend to sing in the winter shortly before mating season. They sing most often at sun-rise and almost never sing while in flight. Each individual Cowbird is thought to have an extensive repertoire. Brown-headed Cowbirds also use their eyesight to distinguish appropriate host species and for communicating among themselves.

What do they eat?

Brown-headed cowbirds often feed on the ground, away from vegetation. Their main food items are seeds and insects. They sometimes hunt in the air, looking for slow flying insects. Their diet is nearly 75% 'weed' seed, with most of the remaining 25% made up of grasshoppers and beetles.

What eats them and how do they avoid being eaten?

Cowbird eggs can be lost when host species reject them. Not all hosts reject cowbird eggs, but when they do, they may push them out of the nest (for example, robins and catbirds), bury them under a new nest lining (for example, yellow warbler), or desert the nest.

Predators on fledgling cowbirds include blue racers, black rat snake, and blue jays. Raptors and owls may also prey on cowbirds as adults. A wide range of nest predators probably takes brown-headed cowbird nestlings, along with those of their hosts, including blue jays, raccoons, skunks, opossums, American crows, northern shrikes, and snakes.

Cowbirds have been known to mob great horned owls.

What roles do they have in the ecosystem?

Not only do cowbirds, provide food for many animals, they also help to control insect populations and disperse seeds.

Do they cause problems?

Fragmentation of forest habitat in North America has resulted in a great increase in the edge habitats favored by Brown-headed Cowbirds, and a reduction (and in many places an elimination) of forest-interior habitats that they do not penetrate. As a result, a number of other forest birds' nests are now being used by Brown-headed Cowbirds at a much increased rate. This parasitism may be one cause in the general decrease in numbers of songbirds in North America.

How do they interact with us?

The cowbird eats many insects which are pests to humans.

Are they endangered?

Brown-headed Cowbirds are common. They do, however, pose a threat to the populations of other birds, such as the Kirtland's Warbler, Black-Capped Vireo, and Least Bell's Vireo, whose small populations are frequently parasitized by Brown-headed Cowbirds. This has led to programs that involve trapping and killing of Brown-headed Cowbirds at specific breeding areas where other species are threatened.