Female frogs feign death to escape from males.

Female European frogs will feign death to avoid mating if several males climb onto their backs at the same time during the breeding season.

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Researchers have discovered that female frogs develop several ways to avoid mating, including rolling around, croaking, and even feigning death. They published their findings on October 11 in the journal Royal Society Open Science. European frogs ( Rana temporaria ) are known for their explosive breeding behavior, often gathering dozens of individuals to mate in ponds and lakes. Typically, the number of males far exceeds the females, meaning six or more males may compete to climb onto a female's back at a time. In some cases, females can be killed inside these mating spheres, according to Carolin Dittrich, a researcher at the Natural History Museum in Berlin.

However, female frogs have developed several techniques to avoid mating. "Instead of being passive and helpless, we found that female frogs can use three key tactics to avoid males they don't want to mate with, either because they are not ready or unwilling to mate," Dittrich said.

Researchers collected male and female European frogs from a pond during mating season and placed them in tanks filled with water, each tank containing two females and one male. They then filmed the frogs for hours. Of the 54 female frogs approached by the males, 83% responded by lying on their backs. This trapped the males underwater and forced them to release the females to avoid drowning.

The research team also found that 48% of female frogs whose backs were climbed on by male frogs emitted growling and high-pitched hissing sounds. The growling mimicked the calls male frogs typically make to ward off other males. However, Dittrich and colleagues were unsure what the higher-frequency hissing meant. They also observed that one-third of the female frogs lay motionless with their limbs spread wide for about two minutes after being caught by a male frog. They suggested the female frogs were feigning death, although they couldn't prove it was conscious behavior. It could also be an automatic response to pressure.

Younger female frogs are more likely to use all three tactics to ward off males, while older individuals are less likely to feign death. As a result, younger female frogs often escape male approach more easily. It's possible that younger female frogs experience fewer mating seasons, leading to greater stress when males approach and a stronger reaction.