Anti-forced solution of female ducks

In some ducks, the female genitalia is quite complicated to prevent forced mating behavior of males.

Males in some ducks often perform forced sexual intercourse with females.Photo: huntersblind.com.

97% of poultry species do not have penis and vagina. Instead, they (both male and female) have only one hole to excrete and release eggs and sperm. The remaining 3% have penis and vagina, and ducks and geese are among them. However, the males of these species have a bad habit: They often mate with females even when they do not receive the consent of their partners. The ducks' cock and the goose are big enough to fit into the female vagina, so they can mate with the girls at all times even if they are not approved.

But in a recent study, the ornithologists from the University of Sheffield (UK) found that the sexual organ of the female in many species of the duck family has evolved to prevent the 'rape' behavior of those rude guy.

The team examined the genital organs of 16 wild duck species. They found that the penis of some species is smooth, but many other species have spines or grooves. The vagina of some species has many spiral-shaped grooves clockwise. These grooves can prevent mating behavior of males because they are twisted in the opposite direction from the grooves in the penis. The vagina of some other species has up to 8 bags on either side of the wall to prevent fertilization by keeping undesirable sperm. In addition, males can mistakenly think of those bags as the entrance of the egg nozzle. Their penis will stop at fake bags and ejaculation. Then the sperm will be locked up immediately.

It is worth noting that these characteristics only appear in species where males are known for 'rape' behavior. Other species have relatively simple genital organs.

'The inner vaginal structure is like a maze. It can prevent deep penetration of the penis or cause sperm to get lost , 'said Tim Birkhead, the lead researcher.

Birkhead argued that the peculiar traits in the duck's vagina show an 'arms race' in which the right to be active in the sex game is feminine. If the male has a long and complex penis to be able to mate, the female's vagina "counteracts" by creating characteristics that prevent the penis from penetrating.

'Our research shows that females in birds do not remain passive in their efforts to combat the sexual abuse of males with large penis , ' Birkhead concludes.