This species does not build a nest nor does it incubate its eggs. It is known as a parasitic species: it lays in other birds' nest, often removing an egg from that nest at the same time. When food is abundant in the environment, female Cowbirds can lay almost daily throughout the nesting season. At the pace of about one egg per day, a single female can lay as many as 40 eggs in the same season. These eggs are usually added to nests when the other bird has not laid all of its clutch. Many birds are parasitized by the Cowbird, the most common species being the Yellow Warbler, the Song Sparrow, the Red-eyed Vireo, and the Chipping Sparrow. The literature reports that Cowbird eggs have been found in nests of over 220 species across North America, mostly passerines. Of these, about 145 species have been known to rear cowbird young. Other species, like the American Robin and Blue Jay, usually throw out of their nest any Cowbird's egg, although a small percentage of these birds' nests have been found containing one........."BIRD STUDIES CANADA - PROJECT NESTWATCH"