In early 2017, it was reported that someone saw a Japanese macaque (snow monkey) mounting a Sika deer on Yakushima Island in southern Japan. Despite widespread skepticism that there was indeed some odd and extremely rare inter-species sex going on Yakushima Island, male researchers in Japan quickly decided to do a study. To insure credibility, they put a female scientist in charge of it and invaded Minoo, a monkey-and-deer-filled city north of Osaka, with cameras. Their perseverance was rewarded with sightings of scores of snow monkeys, both male and female, mounting Sika deer, both male and female, and positive proof that the intent was sexual relations. Really! (There's video here.)
“Our comparative description of monkey-deer versus monkey-monkey interactions supported the “heterospecific sexual behavior” hypothesis: the mounts and demonstrative solicitations performed by adolescent female Japanese macaques toward sika deer were sexual in nature.”
In her best scientific-speak, Dr Noëlle Gunst-Leca, professor at the University of Lethbridge in Canada and co-author of the study published in the Archives of Sexual Behavior, says they saw the monkeys bonking the deer and some of the monkeys were enjoying it. The deer? Not so much, although the researchers said that many seemed to tolerate it. (Sound familiar?)
Actually, the research in Minoo has been going on since 2012, where the scientists first noticed the behavior and were surprised to find that the monkeys caught in the act were all adolescent female macaques. In an interview with The Guardian, Gunst-Leca says they compared the inter-species “mountings” with the common female-to-female interactions that young female macaques have, which end with sexual satisfaction by at least one party. (Is it getting warm in here?)
Gunst-Leca and her team saw 258 separate mounts with 13 ending up in a happy ending for the female monkey. Surprisingly (at least to the researchers), adult male deer were the most receptive to the monkeys – standing quietly and often continuing to graze while being humped in "a temporary, but exclusive, sexual association," Another surprise they found was that when the female monkeys found a male deer who liked (or at least tolerated) what was going on, they would fight over him.
"(Other females}successfully displaced the original adolescent female mounters and took over the deer to start their own heterospeciﬁc consortships."
As they became more comfortable with the deer, the young female monkeys would purse a "particular target" and make standard monkey mating calls.
Is this a safe-sex way for young female macaques to learn about sex? Possibly, especially when there are more females than males and the males are picky. The monkeys have been know to ride deer in what looks like playing and the young females who had accidental “satisfaction” as a result may be seeking it again. Or it could be something else, says Gunst-Leca.
"The monkey-deer sexual interactions reported in our paper may reflect the early stage development of a new behavioural tradition at Minoo."
Uh-oh. In any case, when it comes to sex, you can be sure something else will happen.
“Future observations at this site will indicate whether this group-specific sexual oddity was a short-lived fad or the beginning of a culturally-maintained phenomenon.”
Pass the popcorn!