The Lake Duck is a small South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

n stiff-tailed duck

Stiff-tailed duck

The stiff-tailed ducks are part of the Oxyurinae subfamily of ducks. All have, as their name implies, long stiff tail feathers, which are erected when the bird is at rest. All have relatively large swollen bills.These are freshwater diving ducks...

. It is also called the or Argentine Blue-bill, Argentine Lake Duck, or Argentine Ruddy Duck.

The Lake Duck occurs in Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

, Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

, Paraguay

Paraguay

Paraguay , officially the Republic of Paraguay , is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to the east and northeast, and Bolivia to the northwest. Paraguay lies on both banks of the Paraguay River, which runs through the center of the...

, and Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 in southern South America.

It is notable for possessing, in relation to body length, the longest

Largest body part

The largest body part is either the largest given body part across all living and extinct organisms or the largest example of a body part within an existing species. The largest animals on the planet are not the only ones to have large body parts, with some smaller animals actually having one...

 penis

Penis

The penis is a biological feature of male animals including both vertebrates and invertebrates...

 of all vertebrates; the penis, which is 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 is theorized that the remarkable size of the spiny penis with its bristled tip 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

Brush

A brush is a tool with bristles, wire or other filaments, used for cleaning, grooming hair, make up, painting, surface finishing and for many other purposes. It is one of the most basic and versatile tools known to mankind, and the average household may contain several dozen varieties...

.

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 of the forced copulations do not result in successful fertilisation.