LITCHFIELD, Conn. — “This guy’s the champion,” said Patricia Brennan, a behavioral ecologist, leaning over the nether regions of a duck — a Meller’s duck from Madagascar, to be specific — and carefully coaxing out his phallus.

The duck was quietly resting upside-down against the stomach of Ian Gereg, an aviculturist here at the Livingston Ripley Waterfowl Sanctuary. Dr. Brennan, a post-doctoral researcher at Yale University and the University of Sheffield, visits the sanctuary every two weeks to measure the phalluses of six species of ducks.

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.