|Yellow Warbler Nest|
From Wikipedia: "This bird is a brood parasite: it lays its eggs in the nests of other small passerines ,particularly those that build cup-like nests. The Brown-headed Cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors. The young cowbird is fed by the host parents at the expense of their own young. Brown-headed Cowbird females can lay 36 eggs in a season. More than 140 different species of birds are known to have raised young cowbirds." Another interesting fact, is that it seems that Brown-headed cowbirds will periodically check on the eggs and young after the deposit them, and if the host species has gotten rid of the egg, the cowbird sometimes will attack the nest and destroy it, and when the host species bills another nest, the cowbird will lay eggs in the new nest.