At a presentation here this week […] researchers described their observations of […] Lesser Scaups and Ruddy Ducks (pictured). During the normal mating season, the penises of Lesser Scaup ducks grow about 4 centimeters longer than average, and those of Ruddy Ducks grow about 15 centimeters longer. But when the team made several Lesser Scaup males compete for just a few females, their penises grew up to 25% longer than normal. The researchers say this is the first example of social competition driving genitalia size in vertebrates.
Science NOW refers to the presentation called ‘Social environment affects penis size in waterfowl’ authored by Brennan, Gereg, Goodman and Prum of Yale University. We look forward to see their study published. Earlier work of Patty Brennan on duck genitals was reviewed here.