A female Song Sparrow feeds a juvenile Brown-headed Cowbird.
The Brown-headed Cowbird is the only brood parasite common across North America. A female cowbird makes no nest of her own, but instead lays her eggs in the nests of other bird species, who then raise the young cowbirds.
The Brown-headed Cowbird lays eggs in the nests of many different species of birds. Recent genetic analyses have shown that some female cowbirds will use a number of different hosts, but most females specialize on one particular host species.
Social relationships are difficult to figure out in birds that do not build nests, but male and female Brown-headed Cowbirds are not monogamous. Genetic analyses show that males and females have several different mates within a single season
