Molothrus ater
The cowbird is quickly becoming one of the most hated native birds in North America for its nest parasitism. Historically, Brown-headed Cowbirds followed bison herds-they now follow ranch mammals-and their nomadic lifestyle makes it impossible to tend a nest; instead, cowbirds lay their eggs in the nests of other songbirds. Many of the parasitized songbirds do not recognize the cowbird eggs and incubate them and raise the young cowbirds as their own. As the rapidly growing cowbird develops, it often outsizes its foster parent, whose own offspring often get squeezed out of the nest or die from lack of food. Cowbirds now parasitize more than 140 bird species in North America; the expansion of ranching and the fragmentation of forests has significantly increased the cowbird's range. Despite individual tragedies, however, many songbird's have adapted to the cowbird's parasitism. |
I.D.: Male: glossy green-black plumage; soft brown head; short, squared tail; dark eyes; conical bill. Female: gray-brown plumage overall; slight streaking on underparts; dark eyes. Size: L 6-8 in. (15-20 cm). Range: common migrant and summer breeder throughout the Rockies. Habitat: fields, shrublands, forest edges, roadsides, mountain meadows, landfills, campgrounds, day-use areas and around large mammals up to the subalpine. Nesting: no nest is built; female lays up to 40 eggs a year in the nests of other birds, usually 1 egg per nest, but exceptionally up to 8 (probably from several different cowbirds); eggs hatch after 10-13 days. Feeding: gleans the ground for seeds, waste grain and invertebrates, especially grasshoppers, beetles and true bugs. Voice: call is a squeaky, high-pitched wee-tse-tse; song is a high, gurgling bubble-bubble-zeee. Similar Species: Rusty Blackbird and Brewer's Blackbird: lack the contrasting brown head and darker body; slimmer bills; longer tails. Common Grackle: much longer tail; larger. |
