Here we collect information about the sexual behaviour of animals. We have already some information about
Often "nonstandard" sexual activities - oral or anal sex, homosexual or pedosexual relations, masturbation and so on - will be called not natural. If such arguments are used, the facts about the real behaviour of different animals are a good answer. To describe a behaviour which is widely distributed among higher animals as "not natural" seems nonsense.
But, I think, naming a behaviour "natural" or "not natural" is in general not a very good idea. Remark that defining "natural" as "animals do it" is also nonsense. Even if no animal shows some behaviour, this behaviour may be very natural for human beings (speaking, thinking). On the other hand, there is also a lot of behaviour among animals (eating children, killing the male partner after sex) which is obviously also "not natural" for human beings.
And now, here we have a domain where it is reverse: Some higher animals need sex education in childhood, but we assume that for human beings the instincts are sufficient. Or, may be, human children need sex education too?
I think, that without frequent body-contact with others not only the young monkey will be abnormal, emotionally troubled and asocial.
De facto, sexual education for children is forbidden. Or, do you thing some abstract remarks about the biological facts of procreation is sex education? I don't think it's this children (and animals) need.