I did not, as you are well aware, say "no animal". I was referring to those anomalies in the animal/plant kingdom that might have a biological disposition towards same-sex mating, of which none are mammals, and the mating is done strictly for propagation, not for any sexual pleasure.
Moreover, what does this have to do with the claim that "homosexuality is not natural".
It's not natural in human beings. If it were then you'll have to explain how you folks intend on propagating...within your own means, i.e., without borrowing from the heterosexuals.