Promoters of the "gay" agenda say this all the time. But I haven't seen any research that shows that any animals *prefer* their own sex when the opposite sex is available.
Also, many animals eat their young, are never monogamous, live in herds, don't build houses, etc. So why does the fact (if it is a fact) that SOME animals screw members of the same sex occasionally have anything to do with whether SSAD is normal or not for humans?
Might as well ask if monogamy is normal or biological for humans. And some moral relativists have asked that, and decided it isn't. And that is just an excuse for promiscuity. Humans have something animals don't - conscience, and free will.