Weekend Birdery: The Strange Sex Life of Muscovy Ducks
We interrupt our usual programming for a quick note about the evolution of duck penises. Specifically, that of the Muscovy duck. A Muscovy drake’s penis is extraordinarily long and shaped like a corkscrew.
Muscovy ducks in flagrante
A brief aside: one will not fail to note that Muscovy ducks are rather ugly, to human eyes, primarily due to the bulbous caruncles they have around their faces. To relieve you of any unwanted mental images, I’ve also included a picture of a Muscovy chick below, which is suitably adorable.
Research by Yale’s Patricia Brennan (written up here by Ed Yong and here by Carl Zimmer) sets out to explain what you are no doubt wondering yourself: why corkscrew penises?
The answer: sex wars. Male and female Muscovies have been caught up in an evolutionary arms race of sex-organ development. Ed Yong:
Many ducks form bonds between males and females that last for a mating season. But rival males often violently force themselves onto females. To gain the edge in these conflicts, drakes have evolved large corkscrew phalluses, lined with ridges and backward-pointing spines, which allow them to deposit their sperm further into the female than their rivals. These extreme penises of ducks are even more unusual because 97% of birds lack any penises whatsoever.
But female ducks have developed countermeasures. Their vaginas are equally long and twisting, lined with dead-end pockets and spirals that curve in the opposite direction. They are organic chastity belts, evolved to limit the effectiveness of the males’ lengthy genitals. Two years ago, Brennan showed that duck species whose males have the longest penises tend to have females with the most elaborate vaginas. Now, she has found further evidence that these complex genitals are the result of a long-lasting war of the sexes.
The new evidence includes some amazing videos of the ducks’ ballistic penises. Definitely good for a “woah, dude!” moment.
Who’s winning the war of duck genitalia? Yong says it’s the females. Because of their convoluted vaginas, forced matings result in offspring only 3% of the time.
Suitably adorable Muscovy duckling
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