Duck Genitalia Tells an Evolutionary Tale

Did you know ducks have probably the most interesting genitals of all bird species? The evolution of the enormous duck phallus has been driven by the complexity of the female's even more complex oviduct, according to research published today in PLOS One.

When she first visited in January, the phalluses were the size of rice grains. Now many of them are growing rapidly. The champion phallus from this Meller’s duck is a long, spiraling tentacle. Some ducks grow phalluses as long as their entire body. In the fall, the genitalia will disappear, only to reappear next spring.

The anatomy of ducks is especially bizarre considering that 97 percent of all bird species have no phallus at all. Most male birds just deliver their sperm through an opening. Dr. Brennan is investigating how this sexual wonder of the world came to be.

It gets way better. Also of note is the fact that a female researcher, Patricia Brennan of Yale, made the discovery. Previously, scientists believed it was male competition that led to the very long phalluses, but no one had bothered to look at the female duck's genitalia.

The image shows mallard genetalia, a species with a long phallus and high levels of forced copulations (more on that in the story), in which females have very elaborate vaginas (size bars = 2 cm).

In Ducks, War of the Sexes Plays out in Genetalia [The New York Times]