Lake duck
The Argentine lake duck is a small, South American stiff-tailed duck. It is also called the Argentine blue-bill, Argentine blue-billed duck, lake duck, or Argentine ruddy duck.
Description
The lake duck grows to. Females weigh and males. Males can be distinguished from Andean duck, a similar species, by being smaller and having a flatter head.Penis
The lake duck holds the Guinness World Record for having the largest avian reproductive organ, from a specimen in Córdoba, Argentina that had a penis measuring. It also has the longest penis of any vertebrate in relation to body length. The penis, which is typically coiled up in flaccid state, can reach about the same length as the animal itself when fully erect, but more commonly is about half the bird's length. It has a soft tip and spiny base. It is theorized that the size of their spiny penises with bristled tips may have evolved in response to competitive pressure in these highly promiscuous birds, removing sperm from previous matings in the manner of a bottle brush.Although most male birds have no penis, ducks have a long corkscrew penis, and the females have a long corkscrew vagina, which spirals in the opposite direction. The males often try to force copulation, but the complex mating geometry allows the females to retain control—most forced copulations do not result in successful fertilization.