Eideard

Female ducks have evolved an intriguing way to avoid becoming impregnated by undesirable but aggressive males endowed with large corkscrew-shaped penises: vaginas with clockwise spirals that thwart oppositely spiraled males…

“In species where forced copulation is common, males have evolved longer penises, but females have coevolved convoluted vaginas with dead-end cul-de-sacs and spirals in the opposite direction of the male penis,” said Patricia L.R. Brennan, lead author of the paper…“This coevolution results from conflict between the sexes over who is going to control fertilization.”

The research builds upon a 2007 Yale study that first described the strange morphology of a duck’s sexual organs. While most birds have no phalluses, ducks turn out to have relatively large, flexible penises—up to 20 centimeters—tucked inside their bodies. During sex, male ducks extend, or evert, their phalluses inside the female. Brennan and her Yale colleagues used high-speed video to document the erection of the duck penis for the first time and found the whole process takes less than half a second—an act the Yale team described as “explosive.”

Such large phalluses are supposed to give males a reproductive advantage when there is much forced mating. However, the Yale team hypothesized that females could make copulation difficult for the males with their complex genitalia…

Cripes. I thought finding a quiet place to park was the toughest challenge to sex in the wild.