A Japanese macaque has been recorded attempting to mate with a female sika deer. Scientists say this is only the second time a mating attempt between two distinct species has been documented, with the first being fur seals forcing intercourse on king penguins – before killing and eating them.

Scientists led by French animal behaviour expert Marie Pelé recorded the event on Yakushima Island, South of Japan. They had been observing the monkeys as part of a wider project relating to the cultural behaviours of Japanese macaques, the book for which has now been released.

In November last year, they saw an adult male Japanese macaque trying to have sex with two different female sika deer. Publishing their observations in the journal Primates, they said the male displayed "sexual mounts" on the deer and chased off other males who came near – apparently guarding it. The male showed no aggressive behaviour towards any of the deer.

"A first deer seemed to accept to be ridden by the male macaque," they wrote. "The male mounted the deer and displayed some copulation behaviours (about 15 movements over a period of 10s) before dismounting. No penetration occurred (the penis of the macaque was not directed at the genital area, but at the back of the sika deer), probably due to differences in morphology/size.

monkey sex deer
The Japanese macaque attempting to mate with the female deerAlexandre Bonnefoy

"However, ejaculation seemed to occur as the deer was seen licking the seminal liquid after the mount. The male then attempted to mount another female deer that did not accept the sexual behaviour as she attempted to escape/remove the macaque by moving, increasing her speed, turning around and displaying threats."

The team said eventually both animals disappeared off into the forest and they do not know if the male continued to follow the deer. Discussing the behaviour, they said that unlike the seal/penguin case, there did not appear to be any harassment or penetration. Furthermore, they say the behaviour of the deer appears to indicate the sperm is a "good source of protein".

Researchers think the behaviour is an extension of play behaviour already known – where the macaque rides the deer. They believe the macaques may do it because there is limited access to female macaques. They added that further research will be needed to understand the evolution of interspecific mating behaviour.

monkey sex deer
Findings appear in the journal PrimatesAlexandre Bonnefoy