Biological Exuberance: Animal Homosexuality and Natural Diversity

An oft-repeated claim about homosexuality is that exclusive, lifetime, or “preferential” homosexual activity is unique to human beings, or at least rare among animals (especially among primates and other mammals). This is really a question of sexual orientation—that is, to what extent do animals engage in sexual and related activities with members of the same sex without also engaging in such activities with members of the opposite sex? In fact, exclusive homosexuality of various types occurs in more than 60 species of nondomesticated mammals and birds, including at least 10 kinds of primates and more than 20 other species of mammals.⁹ In this section we’ll consider these various forms of homosexual orientation and compare them to the wide variety of bisexualities that are also found throughout the animal world.

When discussing the question of exclusive homosexuality, several factors need to be distinguished: the length of time that exclusivity is maintained (short-term versus long-term, including lifetime), the social context and type of same-sex activity involved (pair-bonding versus promiscuity in nonbreeding animals, for example), the type of animal involved (e.g., mammal versus bird), and the degree of exclusivity (e.g., absolute absence of opposite-sex activity versus primary homosexual associations with occasional heterosexual ones, and vice versa). These factors combine in various ways and interact with each other to produce a number of different patterns. To begin with, we will consider long-term or extended exclusivity, since this pattern appears to be the most contested as to its existence among animals. Because species vary widely as to their life expectancy, onset of sexual maturity, and period of adulthood, it is difficult to come up with an absolute definition of long-term that has wide applicability. For the purposes of this discussion, though, we will somewhat arbitrarily consider homosexual activity that continues for less than two consecutive years (or breeding seasons) to be short-term, while anything continuing longer is considered extended or long-term, with the understanding that the latter category includes a wide spectrum of possibilities, anywhere from 3 years to a life span of over 40 years.

The only way to absolutely verify lifetime exclusive homosexuality is to track a large number of individuals from birth to death and record all the various homosexual or heterosexual involvements they have. Needless to say, this is a difficult task to accomplish (especially in the wild) and has been achieved for only a few species—indeed, in many cases the comparable evidence for lifetime exclusive heterosexuality is not available either, for precisely the same reasons. Nevertheless, in at least three species of birds—Silver Gulls, Greylag Geese, and Humboldt Penguins—fairly extensive tracking regimes have been conducted, and individuals who form only homosexual pair-bonds throughout their entire lives have been documented. In some cases these are continuous pair-bonds that last upward of 15 years in Greylag Geese and 6 years in Humboldt Penguins (until the death of the individuals involved), while in other cases (e.g., Silver Gulls) individuals may also have several same-sex partnerships during their lives (either because of “divorce” or death of the partners).¹⁰

While absolute verification of lifetime homosexuality is not directly available for other species, extended periods of same-sex activity, perhaps even lifelong, are strongly suggested. In Galahs, Common Gulls, Black-headed Gulls, Great Cormorants, and Bicolored Antbirds, for example, specific homosexual partnerships have been documented as lasting for as long as six years (or individuals having several consecutive homosexual associations for that length of time); in most of these cases the absence of heterosexual activity for at least one partner has been documented or is highly likely. In many other bird species, same-sex partnerships that last anywhere from several years to life probably also occur: Black Swans, Ring-billed Gulls, Western Gulls, and Hooded Warblers, for instance. Although these durations have not been confirmed in specific individuals, homosexual pairs that continue for at least two years or birds who consistently form same-sex pairs for that time have been verified.¹¹ In still other cases, long-term same-sex bonds undoubtedly occur because homosexual pairs in these species typically follow the pattern of heterosexual pairs, which are usually lifelong (or of many years duration): Black-winged Stilts, Herring Gulls, Kittiwakes, Blue Tits, and Red-backed Shrikes, among others. Finally, it must also be remembered that in many animals (e.g., Pied Kingfishers), same-sex (and opposite-sex) pair-bonds that last two to three years can still be lifelong, owing to the relatively short life span of the species.