My first thought is the possibility that either the monkey or the deer, or both of them, may have (in some way) ingested some kinds of new-to-them, manufactured hormonal substances (particularly xenoestrogens), possibly from plastics discarded in the area (plastics which may also include chorines and bisphenol-A components, with the same results), or from pesticides, which could come to their living area by air or by water, or (possibly) from them eating plants in that general area which might have been treated with pesticides.
I would really like to see the results of some screening tests for hormonal, or hormonal-type, substances which are either new to, or out of physiological balance within, either or both species.
On the other hand, this "new" behavior could be an innovative form of intentional inter-species friendships...in which case (as with humans) it could simply be a form of communication!! :)
Edited 1 time(s). Last edit at 12/16/2017 08:15AM by Tevai.
It's not quite as expected. It's mainly the female monkeys that are mounting and riding the male deer (who don't seem to have an issue with it.) If a deer has a problem with it, the deer rears up and unseats the monkey.
They already have interspecies cooperation in that the deer eat food that the monkeys have foraged.
summer Wrote: ------------------------------------------------------- > They already have interspecies cooperation in that > the deer eat food that the monkeys have foraged.