To begin, ducks are unlike 97% of the avian variety of species in that they have penises. They are among the best equipped, in terms of body ratio, of all vertebrates. For example, a 1-pound, foot-long lake duck has the longest of all with a member that is 4 inches longer than its body. Another interesting fact is that duck penises grow back every mating season, being stored at about 10% its original size until it is time for use. Duck penises are also not straight, but rather they have a cork screw, spiral shape to them. Due to this, the female reproductive system is also cork screw in shape.
Many duck species skew the male. This means the females can be pickier in their choice of mate. For a male duck to catch a female, he typically must have colorful plumage plus have an elaborate dance or mating ritual as well as beautiful mating calls. In many of these cases, the males don’t meet the standards of a female, so they resort to other means. Often times, mediocre males participate in forced mating. These are otherwise known as socially organized “gang rapes” that are “violent, ugly, dangerous and even deadly” and sometimes end in the death of the female. This demonstrates a selfish male evolutionary strategy that is at odds with the evolutionary interests of the entire species. In order to pass down their genes, these ducks are disturbing the natural order of selection. Since this has become common in many duck species, females have adapted their own defense with an increasingly elaborate anatomy. This includes, sharp turns in her reproductive canal that act almost as teeth, making it harder for ducks to inseminate during forced sexual encounters. Below is a video of an aggressive male attacking a female.
Some ducks and most birds have “moved away from” this forced sexual encounter. This means no more elaborate reproductive tracts. Instead, female and penis-less male birds rub their cloaca (openings that house testes or ovaries) together in what’s called a “cloacal kiss” an act that shows the power of natural selection.
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