Actually by your own religious texts, they do.

Homosexuality, for example, is stated to be a sin in several verses of the Bible. However, many species of animals are dependent on homosexual behaviors to insure the continued social cohesiveness of their group. Take the bonobo, one of our closest genetic relatives. As a rule they do not discriminate between male or female when choosing sexual partners, and engaging in some form of copulation is common behavior when strengthening emotional bonds, celebrating a new source of food, and re-establishing emotional bonds after a fight. It's very fascinating and you can read more about it on wikipedia.

They're far from the only animal species to engage in homosexual copulating or co-parenting, just the one that I can remember at five in the morning. Dogs also engage in homosexual behavior; I'm sure you've heard of a friend's friend's dog that will only display mating behavior toward a dog of their own gender. Lions as well; female lions can and will gather a pride of their own, even growing a mane like a male lion and mounting the other females like a male lion would. Granted, our limited knowledge of the phenomenon is thus far pointing toward these lionesses being intersex, which is an entirely different argument about whether transgender and intersex beings are sinful by their very existence. I hope you'll understand if I don't want to veer that far off topic.

These behaviors are entirely natural; and, biblically speaking, a sin.

(As an aside, I want to make it clear that I consider exactly zero of the above mentioned a sin or what have you. My brethren in spirit extend into the animal kingdom and I think that's a beautiful thing. <3)