Mating season has taken a strange turn for two normally platonic species on Japan's Yakushima Island.
The Japanese macaque — better known as the snow monkey — has a good thing going with the island's population of sika deer. As noted by a study in Primates, the monkeys groom the deer, drop food from the trees while foraging (which the deer eat) and poop (which the deer also eat). In return, the deer let themselves be ridden by the macaques — but just as friends. Until one lonely, troopless male was observed attempting to bang two of them.
Things went as well as one could expect with the first deer, considering deer and monkeys are wildly different species whose respective genitalia aren't generally designed to interact. As the study notes, "no penetration occurred... However, ejaculation seemed to occur as the deer was seen licking the seminal liquid after the mount." Gross!
The lonely monkey made a pass at a second snow deer, but "she attempted to escape/remove the macaque by moving... and displaying threats". Can't win 'em all, bud.
Animals have been observed in the wild boning plenty of things that don't look like them or engaging in sexual behaviour that doesn't result in offspring (bottlenose dolphins sure do love to jerk off). But attempting to bang an extremely distant species is so rare this is only the second time scientists have observed the phenomenon.
Did this snow monkey think it was doing The Sex with another snow monkey and just goofed it up as badly as one can? Probably not. The study's authors are proposing a "mate deprivation hypothesis", which is to say the isolated macaque was a social outcast with no access to a female. Like many a horny idiot of any species, the monkey mistook friendship for flirtation.
Unfortunately, the study ends on a dour note: "We do not know if the male continued to follow the female deer the day after our observations." I almost feel bad for him.