That would be the work of the Brown-headed Cowbird. Cowbirds do not make a nest of their own, and must visit other nests to lay an egg (one per day until finished). She depends on the other species to foster her young. You can learn more about them here: http://nestwatch.org/learn/general-bird-nest-info/brown-headed-cowbirds/
That would be the work of the Brown-headed Cowbird. Cowbirds do not make a nest of their own, and must visit other nests to lay an egg (one per day until finished). She depends on the other species to foster her young. You can learn more about them here: http://nestwatch.org/learn/general-bird-nest-info/brown-headed-cowbirds/