After reports earlier this year of monkey and deer engaging in sexual encounters, researchers have now found another instance of the same behaviour among snow monkeys and sika deer.

The researchers studied the group in Japan and have concluded that what they witnessed could very well be a "new behavioural tradition".

"The monkey-deer sexual interactions reported in our paper may reflect the early stage development of a new behavioural tradition at Minoo," Dr Noelle Gunst-Leca, co-author of the study from the University of Lethbridge in Canada said, quoted by the Guardian.

Speaking about the encounter revealed earlier this year between the macaque and the deer, Gunst-Leca said it was merely one instance and they weren't able to demonstrate the sexual nature of the interaction clearly.

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However, new research with this new group has left the scientists confident it is definitely behaviour of sexual nature.

The study was published in the Archives of Sexual Behavior last week.

The team recorded 12 successful interactions between monkeys, involving six adolescent females, between November 2012 and January 2013 – with a total of 67 mounts by the monkeys. There were also 13 successful interactions of an apparently sexual nature recorded between monkeys and deer between early November 2014 and January 2015, involving five adolescent females and a total of 258 mounts.

The team also found that the adolescent females emitted high pitched calls at the deer when gazing at them, and threw tantrums if the deer walked away, as they do when engaged in sexual interactions with other monkeys.

Since there are no earlier recordings of this type of relationship between monkeys and deer, experts believe this is a new phenomenon, the birth of a new type of sexual relation for the two species.

The investigators say they will continue looking at the patterns of behaviour of the two species to see if the phenomenon continues to develop.

While sexual relations between closely related species are fairly well documented, it is extremely rare to hear about sexual connections between such different species.