It is probably incorrect to speak of homosexual animals or animal homosexuality, because virtually nothing is known about the cognitive aspects of sexuality in nonhuman species (hereafter, animals). In contrast, male homosexual behavior involving courtship, pair bonding, mounting, and other forms of genital contact has been noted in numerous animal species independent of hormonal or neurological manipulation. Some of these interactions involve clear sexual elements, since erections and ejaculation are sometimes observed. Isolated anecdotes concerning male sexual behavior exist for numerous species in nature, but very few studies have focused on this behavior and attempted to place it within a larger constellation of social and sexual behaviors. To date, the most detailed studies of male homosexual behavior in animals have been on birds (razorbills, pukekos, greylag geese), primates (bonobos, mountain gorillas), and domestic livestock (pigs, sheep, goats).