A new study has recorded the rare sexual behaviour that a male Japanese macaque displayed towards a female sika deer in Japan.
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The activity was filmed by during the monkey mating season.
One of the study's authors Alexander Bonnefoy said: "The male mounted the deer and displayed some copulation behaviours, which included about 15 sexual movements over a period of ten seconds, before dismounting."
While researchers believe ejaculation occurred, they don't think there was penetration due to his positioning on her body.
The study hypothesises that this case could be the result of mate deprivation, where males lack adequate access to females.