Monkeys unusual behaviour is only the second recorded observation of sexual interaction between distantly related wild animals
A male snow monkey has been observed attempting to have sex with female sika deer on Japans Yakushima Island, in an unusual example of interspecies mating behaviour.
It is only the second recorded example of sexual relations between two distantly related species.
Snow monkeys and sika deer generally have a symbiotic relationship, with the deer eating fruits dropped from the trees by the monkeys and the monkeys grooming the deer and occasionally riding on their backs.
The latest paper, published in the journal Primates, describes how a low-ranking male monkey was observed repeatedly performing sexual mounts on at least two different female deer. One doe was seen to bolt and run off, but another female did not appear to object, and licked her side after the monkey ejaculated.
This individual showed clearly sexual behaviour towards several female deer, some of which tried to escape whilst others accepted the mount, the paper reports.
Marie Pel, the lead author based at the University of Strasbourg in France, said: No ambiguity is possible, it is clearly sexual behaviour.
The only previous reported case of sexual interactions between two distantly related species, was that of an Antarctic fur seal observed sexually harassing king penguins and in one instance, eating a bird after having sex with it.
This macaque was a non-troop adult male, in other words low in hierarchy, said Pel. He was therefore probably either peripheral or belonged to a group of peripheral males, as other males were observed in the vicinity of the deer.
The monkey was also seen guarding the target of his affection and chasing away other male monkeys who came near.
The scientists said that mate deprivation was the most likely explanation for the unusual behaviour, after also considering the possibility that the male was learning to copulate or had failed to recognise that the deer was a member of another species.
The most realistic hypothesis would be that of mate deprivation, which states that males with limited access to females are more likely to display this behaviour, the researchers conclude.
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