Lake Duck, Oxyura vittata

The Lake Duck (Oxyura vittata) is a petite, South American stiff-tailed duck. It’s also known as the Argentine Blue-bill, Argentine Lake Duck, or Argentine Ruddy Duck. This duck lives in Argentina, Chile, Paraguay, and Brazil in southern South America. These ducks are clumsy on land because their legs are placed so far back. They spend most of their time in water hunting mainly by diving and they very rarely fly.

Lake Ducks are very small. They weigh about 23 oz and about 16 inches in length. They males, or otherwise known as drakes, have a black head, blue bill, and a reddish-brown colored body. The female being less colorful, with a white throat, brown body, and a white horizontal stripe on the side of the head below the eyes. They generally feed on larvae and pupae mostly found under rocks, aquatic animals, plant material, seeds, small fish, snails and crabs.

It’s noteworthy for possessing, in relation to body length, the longest penis of all vertebrates; the penis, which is typically coiled up in a flaccid state, can reach about the same length as the animal itself when fully erect, but more commonly is about half of the length of the bird. It’s theorized that the remarkable size of their spiny penises with bristled tips may have evolved in response to competitive pressure in these highly promiscuous birds, taking away sperm from previous matings in the manner of a bottle brush.

Although more than half of birds have no penis, ducks have a long corkscrew penis, and the females have a long corkscrew vagina, which spirals in an opposite direction. The males frequently try to force copulation, but the complex mating geometry allows the females to hold control. Most forced copulations don’t result in fertilization.

Image Caption: Argentine Blue-bill (Oxyura vittata) at Sylvan Heights Waterfowl Park in Scotland Neck, North Carolina. Credit: Dick Daniels/Wikipedia (CC BY-SA 3.0)