Most birds have no penis. But there are exceptions. Several species of ducks, geese, and swans have an organ like a human penis, which is inserted into the female. These waterfowl belong to the 3 percent of living bird species that retain the phallus found in their reptilian ancestors. Some ducks—such as those brutish male mallards—have impressive counterclockwise corkscrew-shaped, snakelike phalluses that grow as long as their bodies, which they use to deposit sperm as far as possible inside the female reproductive tract, to better their chances of fertilizing her eggs.
