Brown-headed Cowbird (Molothrus ater)

12 May

Centuries ago this bird which forages by walking on the ground probably followed bison herds on the Great Plains, feeding on insects flushed from the grass by the grazers. Today it follows cattle, and occurs abundantly from coast to coast. Its spread has represented bad news for other songbirds.

Cowbirds lay their eggs in nests of other birds. Heavy parasitism by cowbirds has pushed some species to the status of “endangered” and has probably hurt populations of some others. Female may lay nearly one egg per day for several weeks, up to 40 in a season, exceptionally 70 or more. Female often removes an egg from “host” nest before laying one of her own. Known to have laid eggs in nests of over 220 species of birds, and over 140 of those are known to have raised young cowbirds. Young: Fed by “host” parents. Develop rapidly, and leave nest usually after 10-11 days.