Scientists on Tuesday revealed the “highly unusual” behaviour of a male monkey filmed trying to have sex with female deer in Japan — a rare case of inter-species nookie.
Sex between different species is uncommon — particularly among very distant relations. Such mating is mostly fruitless or yields sterile offspring.
But exceptional cases are known to occur, chiefly in domesticated and captive animals, scientists reported in the journal Primates.
In their study — only the second on the phenomenon — a Japanese macaque or “snow monkey” was filmed mounting at least two female Sika deer, much larger than itself.
Without penetration, the young monkey makes sexual movements while riding on the does’ backs on Japan’s Yakushima Island.
On some occasions its impertinence was tolerated but at other times the deer bolted and ran. The monkey ejaculated on the backs of the does, which licked the seminal fluid, researchers said.
“No ambiguity is possible, it is clearly sexual behaviour,” study co-author Marie Pele of France’s CNRS research agency told AFP.
Furthermore, the monkey appeared to “guard” the targets of its affection, chasing away other male macaques.
The scientists speculated the behaviour may be driven by “mate deprivation” in a community where competition for females is stiff, boosted by a surge of hormones in the breeding season.
“This young macaque… did not have access to (macaque) females, but was very excited. It took advantage of the presence of the doe,” Pele said.
Snow monkeys and Sika deer live in close proximity at Yakushima — the deer eat food the monkeys drop from the trees, and sometimes feed on their faeces.
The team said further study is necessary to understand the origins of interspecies sexual behaviour, including zoophilia — when humans are sexually attracted to animals.
The only other study on inter-species sexual behaviour was the much-publicised 2014 report of fur seals forcing themselves on penguins in Antarctica, the authors said.