How does a cowbird parasitize a nest?
Screaming Cowbirds and Giant Cowbirds usually parasitize the nests of closely related species—the Brown-headed Cowbird, very common in North America, and the Shiny Cowbird will lay eggs in the nests of hundreds of different species. Some Brown-headed Cowbirds apparently specialize in parasitizing particular host species. Cowbirds scan for nests in which to lay their eggs. They tend to search near their foraging areas—in agricultural areas where there are abundant seeds, urban areas, and grasslands bordering forests. Thus, host species’ nests in these areas are parasitized more often than nests in other habitats. The female cowbird watches and waits until the host bird begins laying. Then she pays a quick visit to the host nest, lays an egg and leaves. Four or five eggs may be laid in the same host nest, mixed in with the host’s clutch. In some cases, cowbirds remove host eggs from the nest to make room for their own. Recent evidence suggests that if a female Brown-headed Cowbird misses
