Japanese Snow Monkeys Are Having Sexual Contact With Wild Deer, And Scientists Aren’t Sure Why

A photo of macaques also known as snow monkeys in Japan
Koichi Kamoshida / Getty Images

Macaque monkeys, also known as snow monkeys, are getting sexual gratification from wild deer, and scientists aren’t completely sure why. As Inverse reports, there have been viral videos going around showing adolescent female snow monkeys mounting sika deer in a sexual manner. A team of researchers has been investigating this behavior and their findings have been published in the Archives of Sexual Behavior.

The research has shown that it was primarily adolescent female macaques who were mounting the deer. There are a couple of reasons why these teenage primates might be engaging in this sexual behavior. Firstly, sex with male macaques can be life-threatening for them, so they could be looking for a safer way to relieve their sexual tension. This is one of the reasons why they often see female same-sex encounters within this species.

“Small-bodied and vulnerable adolescent female Japanese macaques may prefer to engage in relatively safer sexual interactions with female monkey sexual partners in lieu of riskier sexual interactions with more aggressive male mates,” said study author, Noelle Gunst-Leca, Ph.D., an adjunct assistant professor of psychology at the University of Lethbridge in Canada.

“Adolescent female Japanese macaques may engage in sexual interactions with passive non-conspecific mates, such as stags, for similar reasons,” she added. “We called this the ‘safe sex’ explanation.”

According to Inverse, there’s also a theory that the female monkeys hump the deer to prepare for sexual encounters with male macaques. Over two years, the researchers observed that a group of adolescent female macaques engaged in 13 of these sexual encounters with deer. During these interactions, the monkeys used 14 different positions or “partner combinations.” These liaisons occurred during the animals’ mating season in Japan.

During the sexual contact, the deer are very passive and allow it to happen. As Inverse notes, they are used to being mounted in this way. The deer and the monkey also have a mutually beneficial relationship in that the deer eat the remains of the fruit that the monkeys drop. They also allow the macaques to groom them.

According to the study, there’s evidence that the adolescent female monkeys get sexual satisfaction from the encounters with the deer. Male macaques often don’t choose the younger females in their species as reproductive partners, so it looks like the female adolescents are seeking “release” from outside of their species. The study also found that it’s normally the mature male deer who allow the monkeys to mount them. During the study, two female deer and two young male deer bucked the monkeys off.

As The Guardian reports, a previous study had observed male macaques having sexual encounters with deer. According to the article, this was the second recorded instance of distant species having sexual relations. The previous instance occurred between an Antarctic fur seal and a penguin.