Ruddy ducks are big hit with the females

The saying "size doesn't matter" has been thrown into doubt by the revelation that drakes from a species of duck have greater mating success because of their large penises.

The saying "size doesn't matter" has been thrown into doubt by the revelation that drakes from a species of duck have greater mating success because of their large penises.

Male ruddy ducks not only mate with females from their own species, but have started to attract white-headed ducks impressed by their size, a leading ornithologist said yesterday.

"Their penises are about half their total body length," Chris Mead said. "The male duck doesn't go round being lovey-dovey with just one female. They display in a group and then the female decides which she is going to mate with. She's selecting the male on the basis of what he can offer." In this case, he offers not only pretty colours and a nice bill, but also a large penis.

The female ruddy ducks go for their males because of their size - eight inches - and this is attracting the females of other species, he said. "The female white-headed ducks are preferring the smaller male ruddy duck, because they have bigger penises in relation to their body size than the male white-headed ducks.

"Size is important for these female ducks. This is the first time we've had a decent explanation for the female white-headed ducks preferring the wrong species," he said."The white-headed ducks are in danger of becoming a hybrid species."