Living Amongst Rivals Causes Some Male Ducks To Grow Bigger Penises


Usually the lesser scaup is a rather modest bird, but it holds nothing back when mixed with other males. Tim Zurowski/Shutterstock

Spend enough time amongst a group of guys, and invariably it can descend into a massive dick swinging contest. But it seems that some male ducks living in groups take this competition to the extreme, and start to actually grow longer penises when in the presence of each other.

Most birds, it turns out, don’t actually have genitalia, but ducks are part of the lucky three percent that does. And boy do they make up for it. Male ruddy ducks, for example, can grow enormous spiraled 42 centimeters (16 inches) long penises, which is longer than the bird itself. These twisting wangs have evolved in response to the convoluted and maze-like vagina of the females, in a process known as sexual competition.


But unlike most penis-bearing creatures, the ducks don’t have their monstrous manhood year round, and instead, it grows and shrinks in response to the season. This caught the attention of Patricia Brennan, who wondered that while the duck dicks evolved due to competition with the vagina, do they also compete with the penises of other males when mating season kicks in?


Eversion in the airScience News/Vimeo (Definitely NSFW)

She decided to see whether competition among male ducks during breeding season altered the size the penises grew in two different species that employ two different mating strategies. The first was the rather well-endowed ruddy duck, which is known to be very promiscuous and tends to force the female into sex, while the second was the lesser scaup duck, which forms seasonal pair bonds and thus tends to have a more modest member.


The researchers split both species into two groups, one in which they placed multiple males with a few females, and another in which they simply paired one male with a single female, over a period of two mating seasons. They then measured their dicks. The results, published in The Auk: Ornithological Advances, found that with the lesser scaup ducks, the males in the larger groups did indeed grow bigger penises, presumably in response to the increased competition from the other males. The situation with the ruddy ducks, however, was a little more complicated.

A ruddy proud duck. P. Brennan

They found that in the larger group, a fewer number than expected reached sexual maturity at the end of the first season, with most waiting until the second year. When they did become mature, the ducks grew their penises faster than those housed with just a female, but they did so at different points in time and out of sync. The researchers suspect that the smaller, less dominant males were hedging their reproductive bets, and trying to limit the intense male-on-male competition by becoming sexually active at different times.

The next question to ask will be whether or not the larger penises actually make the males more successful. More penises to come, it would seem. 

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