uniqueness, none is an absolute line of demarcation between human and nonhuman animals. As always, animal sexuality and social life are far more complex and nuanced than previously imagined: perhaps the only true difference in behavior between the species is that people, but not animals, are prone to make simplistic generalizations.
Exclusively Homosexual, Simultaneously Bisexual: Sexual Orientation
—W. J. GADPAILLE, 1980
—ANNE INNIS DAGG, 1984
—PAUL L. VASEY, 19958
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
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.
In mammals, cases of long-term, exclusively homosexual pairing are indeed rare. One example is male Bottlenose Dolphins: the majority of males in some populations form lifelong homosexual pairs, specific examples of which have been verified as lasting for more than ten years and continuing until death. Although the sexual involvements (both same- and opposite-sex) of such individuals have not in all cases been exhaustively tracked, it is quite likely that at least some of these animals have little or no sexual contact with females (since breeding rates tend to be low in Bottlenose communities, with many individuals not participating in reproduction each year and, by extension, possibly throughout their lives).12 Absolute verification in this species, however, may not be forthcoming, since it is virtually impossible to continuously monitor the sexual behavior of all individuals within a given population of an oceangoing species. Bottlenose Dolphins are exceptional, however, in that the homosexual pattern in this species is distinct from the heterosexual one: opposite-sex pair-bonding does not occur among Bottlenose Dolphins. In most other species, homosexual and heterosexual activities tend to follow the same basic patterns, whether this means pair-bonding, polygamy, promiscuity, or some other arrangement.13 Lifetime homosexual couples are not prevalent among mammals, therefore, for the same reason that lifetime heterosexual couples are not: monogamous pair-bonding is simply not a common type of mating system in mammals (it is found in only about 5 percent of all mammalian species).14
Nevertheless, long periods of exclusive homosexuality among mammals have been documented for other social contexts besides pair-bonding. In many species, significant portions of the population do not engage in breeding or heterosexual pursuits for at least a part of their lives. Because some of these animals continue to engage in same-sex interactions, however, they are exclusively homosexual for at least that time, which can be considerable. Among Gorillas, for example, males often live in sex-segregated groups where homosexual activity takes place. The average length of stay in a male-only group is more than six years, although some males remain in such exclusively homosexual environments for much longer. One individual lived in an all-male group for ten years, staying until his death, and nearly a third of the males who joined the group over a thirteen-year study period were still with the group at the end of that time. Likewise, Hanuman Langur males may spend upward of five years in male-only bands in which homosexual activity takes place, and some individuals live their entire adult lives in such groups.15 In a number of hoofed mammals, a similar form of exclusivity based on sex segregation occurs: only a few individual males participate in heterosexual mating, while the remainder live in “bachelor herds” where homosexual activity often takes place.16 Among Mountain Zebras, for example, males stay an average of three years in such groups before joining breeding groups, and some remain their whole lives without ever mating heterosexually. Analogous patterns occur in a number of other species where only a relatively small percentage of males ever breed: antelopes and gazelles, including Blackbuck, Pronghorn, and Grant’s and Thomson’s Gazelles; Giraffe; Red Deer; Mountain Sheep; seals such as Northern Elephant Seals and Australian and New Zealand Sea Lions; and birds such as Ruffed Grouse, Long-tailed Hermit Hummingbirds, and Guianan Cock-of- the-Rock. In some hoofed mammals such as American Bison, a related age-based pattern is found. Males generally do not participate in heterosexuality until they are five to six years old; prior to that time, many engage in homosexual activities, entailing a period of exclusively same-sex activity of up to five years for some
