As anyone who has ever witnessed a chimpanzee proudly screeching and yanking at his bollocks in front of a group of terrified school children at the zoo will surely testify, apes and monkeys aren't exactly conservative when it comes to their sexual exploits.
The hairy primates' unfiltered randy behaviour has seen their plums pressed up against countless car windscreens, in drive-through safaris all over the planet. But now scientists reckon they've spotted an even more lurid trend emerging among a particular species of the horny hominids. And guess what? It's not the blokes this time.
Following reports of - there's no nice way of putting this - monkeys humping deer in Japan earlier this year, similar sexual advances have now been observed several times in macaques of both genders, leading researchers to believe a new behavioural trend is emerging, whether the deer like it or not.
"The monkey-deer sexual interactions reported in our paper may reflect the early stage development of a new behavioural tradition at Minoo," said Dr Noëlle Gunst-Leca, co-author of the study from the University of Lethbridge in Canada.
Sexual interactions between distant related species are very rare, with the only known cases being the sexual assaults of king penguins by Atlantic fur seals.
However, earlier this year, a study revealed a male Japanese macaque had been caught mounting a female Sika deer at Yakushima island in southern Japan. Gunst-Leca - who apparently doesn't have much of an imagination - said it wasn't clear at first what exactly was going on.
"They were dealing with a single anecdotal event between one individual monkey and one individual deer, and the description they provided was short, vague and out of context," she said. "As a result, even the sexual nature of this interaction was not clearly demonstrated."
Since then, Gunst-Leca has authored a new study, aiming to find out whether the intentions of the monkey-deer-relations had in fact been sexual.
Her team travelled to Minoo near Osaka and observed only female snow monkeys mounting deer. They then compared the interactions to sexual ones between adolescent female monkeys.
The team documented 12 successful sexual interactions between the monkeys, involving six adolescent females, between November 2012 and January 2013.
Credit: Jean-Baptiste Luca/YouTube
In addition, 13 successful interactions of a sexual nature were recorded between monkeys and deer between early November 2014 and January 2015. These inter-species incidents involved five adolescent females and a total of 258 mounts.
Unexpectedly, pelvic thrusting was more common when the sexual partner was a deer, as opposed to another monkey.
The research team claim that the behaviour could be the start of a new custom, observing that adolescent females would watch others on the backs of the deer and attempt to copy them.
"It is maybe a new/innovative behaviour that can be socially transmitted and will spread," said Dr Cédric Sueur of the University of Strasbourg, a co-author of the study released earlier this year.
"Monkeys do this according to the sex ratio at the reproductive season: if females cannot have access to males, they can have homosexual relations or relations with a deer."
Featured Image Credit: Jean-Baptiste Leca