Scientists caught a male Japanese macaque red-butted (so to speak) trying to mate with several female sika deer. In the video, a few of the deer try to shake the little monkey off, but others just wait for it to be over.
The video of the attempted interspecies coupling was filmed on Yakushima Island, Japan, in the fall of 2015 — the peak of macaque breeding season. It was published with an academic paper today in the journal Primates, and was first reported by New Scientist.
The macaques and the deer live in the same areas, and regularly interact. For example, the macaques drop fruit and feces on the ground, which the deer eat. The macaques have also been seen riding the deer, possibly as a game, the study reports.
But what’s on the video isn’t just riding. While there wasn’t any penetration, this was clearly sexual behavior, the study authors say. In fact, the macaque male did appear to ejaculate on at least one of the deer and the deer licked the sperm on its back after the macaque dismounted. Still, the macaque didn’t act aggressively or try to coerce the deer, the researchers say. After he mounted the deer, he tried to ward off other males — which would be normal mate guarding behavior, if he were guarding other macaques.
While closely related species are known to interbreed, mating between distant species is pretty rare in the wild. In fact, the authors note that the only other case published in the academic literature was about an antarctic fur seal that sexually harassed king penguins. (Even worse: the seal ate some of the penguins afterwards.)
The researchers don’t think that this particular macaque was just confused. Instead, they think that mate deprivation might be driving the behavior: there just aren’t enough available female macaques for the monkey to have sex with. The macaque was what the authors call a “peripheral” male, a male that's on the edge of the main macaque troop. There are typically no females in the peripheral male groups.
So what do the deer get out of it? Not much, except maybe some nutrition. “[T]he licking behaviour shown by the deer seems to indicate that the sperm could be a good source of protein,” the authors wrote.