Kačeři mají penis do vývrtky
Why are duck penises corkscrew-shaped and how do they mate? | BBC Science Focus Magazinehttps://www.sciencefocus.com/nature/duck-penis-corkscrew/How the battle of the sexes left the duck with an awkwardly long, corkscrew-shaped penis
Ducks' bizarre genitalia is a result of a sexual arms race. Forced mating is common among ducks, so while males' long, flexible penises increase their chances of successfully fertilising a female, the females' anticlockwise vaginas give them a level of control.
"Those complex structures prevent full eversion of the penis of unwanted males, so their sperm ends up closer to the cloacal entrance where the females can get rid of it more easily." That is, Brennan's research found that female ducks can prevent fertilisation from unwanted males.
However, if the female wants to mate with a certain male, she can relax her cloacal muscles to allow easier access.