Run-of-the-mill city pigeons, known as rock doves, build their nests in the nooks and crannies of the concrete cityscape, reminiscent of their native European and Middle Eastern cliffside habitats. Parents typically keep babies, or squabs, hidden and safe until they can survive on their own, usually a month after hatching.

As a result, youngsters are almost fully grown and their feather coloring looks nearly identical to an adults by the time they fly the coop, says Karen Purcell, who leads Cornell Universitys Project PigeonWatch, a grassroots study of feather colorings.