Lake duck

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Lake duck
Argentine Blue bill (Oxyura vittata) RWD.jpg
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Anseriformes
Family: Anatidae
Subfamily: Oxyurinae
Genus: Oxyura
Species: O. vittata
Binomial name
Oxyura vittata
(Philippi, 1860)
Oxyura vittata distribution.svg
Oxyura vittata range

The lake duck (Oxyura vittata) is a small, South American stiff-tailed duck. It is also called the Argentine blue-bill, Argentine lake duck, or Argentine ruddy duck.

The lake duck lives in Argentina, Chile, Paraguay, and Brazil in southern South America.[1]

In addition to holding the Guinness World Record for largest avian reproductive organ,[2] it is notable for possessing, in relation to body length, the longest penis of all vertebrates; 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.[3][4] It is 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, removing sperm from previous matings in the manner of a bottle brush.

Although most male birds have no penis,[5] ducks have a long corkscrew penis, and the females have a long corkscrew vagina, which spirals in the opposite direction.[6] Scientists have suggested that males use their penises to lasso reluctant females.[7] 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.[8]


  1. ^ a b BirdLife International (2012). "Oxyura vittata". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ Largest reproductive organ for a bird:
    The largest penis of any bird is that of the Argentine lake drake (Oxyura vittata) which has been measured everted and unwound at 42.5 cm (16.7 in).
  3. ^ McCracken, Kevin G. (2000). "The 20-cm Spiny Penis of the Argentine Lake Duck (Oxyura vittata)" (PDF). The Auk. 117 (3): 820–825. doi:10.2307/4089612. 
  4. ^ McCracken, Kevin G.; Wilson, Robert E.; McCracken, Pamela J.; Johnson, Kevin P. (2001). "Sexual selection: Are ducks impressed by drakes' display?" (PDF). Nature. 413: 128. doi:10.1038/35093160. 
  5. ^ Found! The longest bird penis ever › News in Science (ABC Science)
  6. ^ Duck genitals locked in arms race | COSMOS magazine
  7. ^ Evolutionary Oddities: Duck Sex Organs > National Geographic
  8. ^ Brennan, Patricia L. R.; Prum, Richard O.; McCracken, Kevin G.; Sorenson, Michael D.; Wilson, Robert E.; Birkhead, Tim R. (2 May 2007). "Coevolution of Male and Female Genital Morphology in Waterfowl". PLoS ONE. 2 (5): e418. doi:10.1371/journal.pone.0000418. PMC 1855079free to read. PMID 17476339. 

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