Molothrus ater
brown-headed cowbird

Cowbirds breed from SE Alaska, through lower Canada, through the entire continental U.S. to central Mexico. They winter throughout this range, and also in southern Mexico and the tip of Florida.

Cowbirds prefer habitats with low or scattered trees among grassland vegetation, such as woodland edges, brushy thickets, prairies, fields, pastures, orchards, and residential areas. Fragmentation of forests has greatly increased the Brown-headed Cowbirds favorite habitat.

The cowbird is a small blackbird with a short conical bill and long, pointed wings. Males appear black with a unique brown head and neck. Females are either dullish gray or brown throughout. The bill is a dull grey, while the eyes are black.

The cowbird rarely hops when on the ground, preferring to walk. It is often found in mixed-species flocks with other blackbirds, such as the Common Grackle. The cowbird gets its name from its 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 to cowbirds near their nesting trerritory.

Cowbirds often feed on the ground, away from vegetation. Their main food items are seeds and arthropods. They sometimes hawk, looking for slow flying insects. In a quantitative anaylsis of the cowbird diet, it was found that nearly 75% of the diet was 'weed' seed, with most of the remaining 25% made up of grasshoppers and beetles.

Fragmentation of forest habitats in North America has resulted in a great increase in the edge habitats favored by cowbirds, and a reduction (and in many places an elimination) of forest-interior habitats that cowbirds do not penetrate. As a result, a number of species of forest birds are now subject to increasing parasitism by cowbirds. Cowbird parasitism may be one cause in the general decrease in numbers of songbirds in North America.

The cowbird eats many insects which are pests to humans.

The cowbird is common. It does, 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 the Brown-headed Cowbird. This has led to programs that involve trapping of the cowbirds at specific breeding areas where other species are threatened.