An adult male has a brown head, and a black body that can appear metallic green. An adult female is a drab brown color overall. In the late summer and early fall, a male that hatched that same summer appears mottled, with plumage coloration that is intermediate between the adult male and female, as it molts the juvenile plumage and gains adult plumage. The bill, legs, and eyes of adults and juveniles are dark black. 19 cm (7.5 in) in length. This member of the Blackbird Family carries its tail upwardly when it is feeding.
In the Southeast, breeding begins in April, peaks in May, starts declining in June, and occurs sporadically through July. The Brown-headed Cowbird is parasitic and therefore builds no nest. The female can lay approximately 40 eggs in one breeding season, usually 1-2 in each host's nest. These birds have successfully parasitized 144 species, mostly passerine birds, with the host adults successfully raising at least one cowbird young. Females are polygynous, sometimes mating with more than one male, and probably maintain some sort of territory. The young usually develop faster than the host young, and are larger and louder as well. The eggs usually hatch after 10-13 days, and the young fledge in 10-13 days. The young are altricial and are raised by the host parents. They are not cared for by the Brown-headed Cowbird adults.
The Brown-headed Cowbird can be seen in almost every habitat, using open woodlands, fields, and the marginal habitat in between. It spends time foraging on the ground eating insects, seeds, grain, and fruits. This bird feeds in fields and is commonly associated with agriculture (cattle pastures, feed lots). The Brown-headed Cowbird is migratory, spending time year round in the southern United States, but occurring only during the breeding season in the northern and mountainous regions of the United States.
The Brown-headed Cowbird occurs throughout the United States and most of North America. In the Southeast, including Georgia, the Brown-headed Cowbird can be seen throughout the year except in southern Florida, where it only winters. Its range has expanded with changes in land use. As more forests have been cleared for agriculture, this change has opened new preferred feeding grounds.
The Brown-headed Cowbird has no population decline, but is considered a conservation problem for many passerine species. Many host species reject Brown-headed Cowbird eggs or abandon nests that are parasitized. If a host accepts the cowbird egg, the chance of raising one of its own young along with the cowbird is greatly reduced. Brown-headed Cowbird parasitism is considered to be one of the reasons for the decline of the Kirtland's Warbler, a northern species which is Federally listed as Endangered. Because of its breeding style is detrimental to other passerine birds, some conservation efforts control its population by removing adult cowbirds.
Similar species include many of the other blackbirds (Family Icteridae). The Brown-headed Cowbird can be distinguished from most of them by variation in color and carrying its tail upwardly when feeding. The most similar species is the Bronzed Cowbird. The adult male Bronzed Cowbird lacks the brown head and has red eyes. The female Bronzed Cowbird is variable in color but darker than the Brown-headed Cowbird female, and also has reddish eyes.