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Ducks and the Ultimate Display of Male Pride

Duck penises are a fascinating subject! There, we’ve said it! Most birds lack penises but male ducks boast long and spiralling phalluses. This strange form of genitalia has evolved as ducks have to engage in cat and mouse antics with females. The female birds possess reproductive tracts which defend them against sexually aggressive males. The spiralled penises help males to overcome this feature of the female anatomy.

Male Competition Inspires Penis Growth


Ducks develop new penises every year and now research has demonstrated that, in some species, male ducks will change how their penis grows when presented with competition from other ducks! When males spend a lot of time with other males their penises start to grow longer! Ducks actually change their penis lengths according to their social group.

Mating Time


When it’s time to mate, female ducks have to watch out because duck penises unfurl in an explosive manner when the birds feel the urge! Around a third of duck mating involves some degree of forced penetration. The females evolved long and twisting reproductive tracts to defend themselves from such assaults but penises then evolved to counter this defence. Female tracts spiral anti-clockwise whilst the males’ penises spiral clockwise. We are betting that you didn’t
know that!

Most forced mating does not result in the fertilisation of eggs as some female ducks have evolved special pouches to trap unwelcome sperm. Ducks have developed their own form of contraception!

New Research


Researchers at Mount Holyoke College, Massachusetts looked at male competition to assess how it influences penis size in a flock. They studied two species, the ruddy duck which is highly promiscuous and the lesser scaup which forms seasonal partnerships. The lesser scaup has a relatively short penis which suggested that penis size could be linked to promiscuity in ducks.

Lesser Scaups and Ruddy Ducks


During the study, some male ducks were kept with other males during mating season, while others were kept with a single female. The lesser scaup duck was found to grow its penis longer when it was around other males during mating season and so was clearly adapting its penis size according to the number of rivals which were present.

The ruddy duck was also shown to have the ability to grow its penis longer and to speed up the growth when it enters sexual maturity. However, only some males experienced growth when housed together. The duck’s penises grew out of sync with each other which suggested that faced with competition, the ducks offset their sexual development from other males. If the ducks mature at different times, they may have a better chance of mating.

So, there you have it. Duck genitalia is truly fascinating and there is probably much more for us to learn about how ducks deal with the competition for mates.

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