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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.〔 In addition to holding the Guinness World Record for largest avian reproductive organ,〔(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).''〕 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. 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,〔(Found! The longest bird penis ever › News in Science (ABC Science) )〕 ducks have a long corkscrew penis, and the females have a long corkscrew vagina, which spirals in the opposite direction.〔(Duck genitals locked in arms race | COSMOS magazine )〕 Scientists have suggested that males use their penises to lasso reluctant females.〔(Evolutionary Oddities: Duck Sex Organs > National Geographic )〕 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. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lake duck」の詳細全文を読む スポンサード リンク
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