The brown-headed cowbird (Molothrus ater) is a small, obligate brood parasitic icterid native to temperate and subtropical North America.

[2] The brown-headed cowbird was described by the French polymath Georges-Louis Leclerc, Comte de Buffon in 1775 in his Histoire Naturelle des Oiseaux from a specimen collected in the Carolinas.

[3] The bird was also illustrated in a hand-colored plate engraved by François-Nicolas Martinet in the Planches Enluminées D'Histoire Naturelle, which was produced under the supervision of Edme-Louis Daubenton to accompany Buffon's text.

[4] Neither the plate caption nor Buffon's description included a scientific name, but in 1783, Dutch naturalist Pieter Boddaert coined the binomial name Oriolus ater in his catalogue of the Planches Enluminées.

[9] Three subspecies are recognised:[7] The brown-headed cowbird is typical for an icterid in general shape, but is distinguished by its finch-like head and beak and smaller size.

The adult female is slightly smaller and is dull grey with a pale throat and very fine streaking on the underparts.

[11] The species lives in open or semiopen country, and often travels in flocks, sometimes mixed with red-winged blackbirds (particularly in spring) and bobolinks (particularly in fall), as well as common grackles or European starlings.

Their population expanded with the clearing of forested areas and the introduction of new grazing animals by settlers across North America.

[12] In 2012, brown-headed cowbirds in northwest Riverside County, CA tested positive for West Nile Virus.

The brown-headed cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors.

[19][20]: 199 Unlike the common cuckoo, the brown-headed cowbird is not divided into gentes whose eggs imitate those of a particular host.

According to one study the cowbird returned to ransack the nests of a range of host species 56% of the time when their egg was removed.