Blue-eyed yellow Warbler

The bright, sweet song of the Yellow Warbler is a familiar sound in streamside willows and woodland edges. This is one of our most widely distributed warblers, nesting from the Arctic Circle to Mexico, with closely related forms along tropical coastlines. Their open, cuplike nests are easy to find, and cowbirds often lay eggs in them. Yellow Warblers in some areas thwart these parasites by building a new floor over the cowbird eggs and laying a new clutch of their own. In one case, persistent cowbirds returned five times to lay more eggs in one nest, and an even more persistent warbler built six layers of nest floors to cover up the cowbird eggs.