|Oxyura vittata range|
In addition to holding the Guinness World Record for largest avian reproductive organ, 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, 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.
- BirdLife International (2012). "Oxyura vittata". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- 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).
- 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. Archived from the original (PDF) on 2008-07-05.
- 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. PMID 11557968. Archived from the original (PDF) on 2006-09-07.
- Found! The longest bird penis ever › News in Science (ABC Science)
- Duck genitals locked in arms race | COSMOS magazine Archived 2008-07-25 at the Wayback Machine.
- 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 1855079. PMID 17476339.