Mick Hartley

Why are male ducks so, um, well equipped? Turns out that it could be the result of a female evolutionary response to the frequency of rape in the duck world. And it took a woman scientist to see it:

Dr. Brennan was oblivious to bird phalluses until 1999. While working in a Costa Rican forest, she observed a pair of birds called tinamous mating. “They became unattached, and I saw this huge thing hanging off of him,” she said. “I could not believe it. It became one of those questions I wrote down: why do these males have this huge phallus?”

A bird phallus is similar — but not identical — to a mammalian penis. Most of the time it remains invisible, curled up inside a bird’s body. During mating, however, it fills with lymphatic fluid and expands into a long, corkscrew shape. The bird’s sperm travels on the outside of the phallus, along a spiral-shaped groove, into the female bird.

To learn about this peculiar organ, Dr. Brennan decided she would have to make careful dissections of male tinamous. In 2005 she traveled to the University of Sheffield to learn the art of bird dissection from Tim Birkhead, an evolutionary biologist. Dr. Birkhead had her practice on some male ducks from a local farm.

Gazing at the enormous organs, she asked herself a question that apparently no one had asked before.

“So what does the female look like?” she said. “Obviously you can’t have something like that without some place to put it in. You need a garage to park the car.”

The lower oviduct (the equivalent of the vagina in birds) is typically a simple tube. But when Dr. Brennan dissected some female ducks, she discovered they had a radically different anatomy. “There were all these weird structures, these pockets and spirals,” she said.

Somehow, generations of biologists had never noticed this anatomy before. Pondering it, Dr. Brennan came to doubt the conventional explanation for how duck phalluses evolved.

In some species of ducks, a female bonds for a season with a male. But she is also harassed by other males that force her to mate. “It’s nasty business. Females are often killed or injured,” Dr. Brennan said…

Dr. Brennan argues that elaborate female duck anatomy evolves as a countermeasure against aggressive males. “Once they choose a male, they’re making the best possible choice, and that’s the male they want siring their offspring,” she said. “They don’t want the guy flying in from who knows where. It makes sense that they would develop a defense.”

Female ducks seem to be equipped to block the sperm of unwanted males. Their lower oviduct is spiraled like the male phallus, for example, but it turns in the opposite direction. Dr. Brennan suspects that the female ducks can force sperm into one of the pockets and then expel it. “It only makes sense as a barrier,” she said.

I’m a little perplexed by this corkscrew business. Does the male need to, you know, spin around? I’m not the keenest birdwatcher, but I think I’d have noticed – in the park, maybe. “Mummy, what’s that duck doing, spinning round on top of that other duck?”

And those orientation problems: “Don’t you just hate it when you’ve lined up a cute dowdy little brown feather, pecked her into submission, then, uh-oh, wouldn’t you know, the bitch is anti-clockwise.”