Ducks ding dongs in face of stiff competition

Alternative title for this science paper: Seven-inch bullies humiliate unsuspecting birds

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Waterfowl situation... Some alpha ducks bully smaller ducks so much when competing for mates that the beta birds' undercarriages barely take off, so to speak, a new study has found.

Ducks are pretty unusual, in that some species temporarily grow their penises for the mating season, and penis shape and size is already diverse – making them ideal for studies of genital evolution. Patricia Brennan, an evolutionary biologist at Mount Holyoke College in Massachusetts, USA, wanted to see whether the aquatic birds’ social environment played a part in the reemergence of the feathered friends’ members.

To test the theory, she and her team at the Livingston Ripley Waterfowl Conservancy in Litchfield, Connecticut, split up two types of ducks – the ruddy duck and the lesser scaup – into two groups: separate male-female couples, and a mixed group of males and females.

In a situation not unlike the start of a night out – and well described in this episode of Flight of the Conchords – the mixed groups involved a good number more men than women (eight to five). However, unlike in the Conchords’ classic, the results revealed that there were not, in the end, too many dicks on the dance floor duck pond – because some of the bloke birdies failed to grow much more than a stub.

Things were fairly straightforward in the groups of lesser scaup ducks: those in a mixed group grew bigger penises, while the penises in the happy couples remained normal.

But a more complicated situation – which saw some ducks fail to grow anything more than a nub – arose (or didn’t, ho ho) in the ruddy duck group. In the mixed sex setting, the biggest male was found to grow and maintain a long penis over the whole mating season, while his puny peers did pretty much the opposite.

“All the other guys, who are smaller than he is, are prevented from growing a penis and keeping it long all season,” Brennan said. “They can grow a penis that’s a bit shorter for just a few weeks or so, but then they shrink back.”

The reason for this penis palaver, Brennan said, is the aggressive nature of the ruddy duck – the dominant male will attack any potential competitors to stop them from mating.

Well, that's a turn-off

By not growing a longer penis, the smaller and weaker ducks are less of a target from the big boy in the pond.

“Essentially, it’s so they won’t get beaten up too badly by the dominant male, because he’ll peck them to control their reproduction,” Brennan said.

The lesser scaup doesn’t behave in this way, explaining why the results were more straightforward in that group.

Brennan’s study, published on Wednesday, looked at the groups of ducks over two years. It found that in the first year only the biggest males grew long penises – many of the ruddy ducks had delayed reproductive maturity.

In the second year, the penis sizes of the ducks that were in a group setting diverged, with the dominant ones growing the biggest penises, which could be about 18cm (7in). The smallest todgers didn’t scrape over the 0.5cm (.2in) mark.

Brennan said that it wasn’t clear whether the effect would be quite so clear-cut in the wild, as the dominant duck’s reign of terror might not last quite so long if he also had to seek out food.

And, she pointed out, the smaller ducks “would probably leave, and try their luck in another pond.” ®


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