Various non-human animal species exhibit behavior that can be interpreted as homosexual or bisexual. This may include same-sex sexual activity, courtship, affection, pair bonding, and parenting among same-sex animal pairs. Various forms of this are found in every major geographic region and every major animal group. The sexual behavior of non-human animals takes many different forms, even within the same species, though homosexual behavior is best known from social species.
Scientists perceive homosexual behavior in animals to different degrees. A 2019 paper states that same-sex sexual behavior has been observed in over 1,500 species. A previous 1999 book by Canadian biologist Bruce Bagemihl states same-sex behavior (comprising courtship, sexual, pair-bonding, and parental activities) has been documented in over 450 species of animals worldwide. Although same-sex interactions involving genital contact have been reported in hundreds of animal species, they are routinely manifested in only a few, including humans. Simon LeVay stated that "[a]lthough homosexual behavior is very common in the animal world, it seems to be very uncommon that individual animals have a long-lasting predisposition to engage in such behavior to the exclusion of heterosexual activities. Thus, a homosexual orientation, if one can speak of such thing in animals, seems to be a rarity." The motivations for and implications of these behaviors are lensed through anthropocentric thinking; Bagemihl notes that any hypothesis is "necessarily an account of human interpretations of these phenomena".
One species in which exclusive homosexual orientation occurs is the domesticated sheep (Ovis aries). "About 10% of rams (males), refuse to mate with ewes (females) but do readily mate with other rams."
In October 2023, biologists reported studies of animals (over 1,500 different species) that found same-sex behavior (not necessarily related to human orientation) may help improve social stability by reducing conflict within the groups studied.
In relation to humans
Applying the term homosexual to animals
The term homosexual was coined by the Hungarian writer and campaigner Karl Maria Kertbeny in 1868 to describe same-sex sexual attraction and sexual behavior in humans. Its use in animal studies has been controversial for two main reasons: animal sexuality and motivating factors have been and remain poorly understood, and the term has strong cultural implications in western society that are irrelevant for species other than humans. Thus homosexual behavior has been given a number of terms over the years. According to Bruce Bagemihl, when describing animals, the term homosexual is preferred over gay, lesbian, and other terms currently in use, as these are seen as even more bound to human homosexuality.
Bailey et al. says:Homosexual: in animals, this has been used to refer to same-sex behavior that is not sexual in character (e.g. 'homosexual tandem running' in termites), same-sex courtship or copulatory behavior occurring over a short period of time (e.g. 'homosexual mounting' in cockroaches and rams) or long-term pair bonds between same-sex partners that might involve any combination of courting, copulating, parenting and affectional behaviors (e.g. 'homosexual pair bonds' in gulls). In humans, the term is used to describe individual sexual behaviors as well as long-term relationships, but in some usages connotes a gay or lesbian social identity. Scientific writing would benefit from reserving this anthropomorphic term for humans and not using it to describe behavior in other animals, because of its deeply rooted context in human society.Animal preference and motivation is always inferred from behavior. In wild animals, researchers will as a rule not be able to map the entire life of an individual, and must infer from frequency of single observations of behavior. The correct usage of the term homosexual is that an animal exhibits homosexual behavior or even same-sex sexual behavior; however, this article conforms to the usage by modern research, applying the term homosexuality to all sexual behavior (copulation, genital stimulation, mating games and sexual display behavior) between animals of the same sex. In most instances, it is presumed that the homosexual behavior is but part of the animal's overall sexual behavioral repertoire, making the animal "bisexual" rather than "homosexual" as the terms are commonly understood in humans.