Homosexuality
Homosexuality is common among animals that are not innately bisexual, especially social species. Both males and females engage in same-sex bonding. Homosexuality has been observed in 1,500 species, from gut worms to fish to birds to primates.
Homosexuality only sometimes excludes heterosexual activity. There are numerous exceptions. Monogamous species, such as penguins, form exclusive same-sex pair bonds.
Rabbitfish reproduce in mass aggregations, but they still pair up for companionship. Not all pair bonds are heterosexual.
25% of black swan pairings are homosexual. The parenting urge remains. Male pairs may steal nests or form a temporary threesome with a female to obtain eggs. Once she has laid, the mated male pair drive the female off.
10% of male domestic sheep refuse to mate with ewes, but readily do so with other rams. Their sexual orientation is quite decided.
