There are no homosexual animals. EXCLUSIVE homosexuality (no interest in opposite sex) does not exist in nature. There are extremely rare cases of bisexuality and next to 0 involve actual penetration, just fake mounting which is a sign of dominance or play.
So what is an exclusive homosexuality? Because i would bet a lot of money that almost all if not all homosexuals are experimenting with the opposite sex. so no one is "exclusive" homosexual if there is to be no interest in the opposite sex.
But a lot of animals have shown homosexual activity, both with sex only and raising own "kids", penguins have done so. its even well documented in zoos also that penguins engage in same sex relationships.