Biological Exuberance: Animal Homosexuality and Natural Diversity

and the reproductive advantages of same-sex coalitions are often questionable. Male Calfbird companions who display together, for example, do not attract females, nor are they more successful at acquiring mating territories or overcoming rivals than “single” males. Male Cheetahs living in same-sex bonded coalitions (pairs or trios) are no more likely to encounter females than are single males (even though the standard interpretation of such bonding is that it enhances males’ reproductive opportunities and access to opposite-sex partners). They may in fact suffer reduced chances of heterosexual mating (and lowered reproductive output) because of competition or direct interference from their companions. Likewise, although coalitions of male Savanna Baboons sometimes cooperate in obtaining or defending female partners, one researcher points out that this is true for only one-quarter to one-third of all such alliances, concluding that most male partnerships serve many purposes besides obtaining mates and may even lack a recognizable “function.”⁶⁰

The case for male pair-bonding being solely a breeding strategy in Bottlenose Dolphins is also far from definitive. Pairing or “coalition” formation between males of this species is often interpreted—and widely cited—as a means whereby the animals obtain heterosexual mates. Although pairs (and trios) of Bottlenose males may cooperatively seek out and herd females for purposes of mating in some populations (e.g., Australia), this is not a uniform aspect of such partnerships, and in many cases it has yet to be documented. Heterosexual matings resulting from such associations have not in fact been observed in the Florida population where the most extensive study of male pairing has been conducted, nor in Ecuador, where it has recently been suggested that paired males may compete for females. In Australia, where herding and mounting of females by paired males have been observed, no “full” copulations involving penetration have actually been documented, so the reproductive status of this behavior is not clear. Moreover, nearly 38 percent of the animals herded by paired males in Australia were not definitvely sexed: researchers simply assumed that they were females. In fact, bonded males in other populations seek out male rather than female sexual partners in at least some contexts. In the Bahamas, pairs or coalitions of adult male Bottlenose Dolphins herd and chase Atlantic Spotted Dolphins; they typically pursue homosexual activities (including full penetrative copulation with other males) during these interspecies encounters. Finally, even if bonded males assist each other in obtaining heterosexual mates, this does not preclude a homosexual dimension to such partnerships—sequential and simultaneous bisexuality are, after all, prominent in this species. Same-sex pairs can form as long as ten to fifteen years before breeding activity commences, and homosexual activity may exist concurrently with heterosexual activity in such pairs once they do reach breeding age.⁶¹

One species in which same-sex activity among males sometimes does attract females is the Ruff. As already noted, however, homosexual behavior in this bird is not limited to contexts in which it might increase opportunities for heterosexual mating. It also occurs among nonbreeding males, when females are not present, and during the nonbreeding season. Similarly, homosexual activity in female Squirrel Monkeys sometimes does arouse the attentions of males. However, it is clear that the participating females engage in such behavior regardless of whether it draws males and even rebuff the advances of males who approach them during such activity. Sometimes heterosexual behavior serves as a stimulant for homosexual activity and not the other way around. Stumptail Macaques, aroused by the sight of heterosexual activity, often initiate same-sex interactions, while in Wolves, Savanna (Yellow) Baboons, and Mountain Sheep, animals watching heterosexual mating often become excited and engage in homosexual activities.⁶²

Even if males of some species are genuinely aroused by sexual activity between females, the evidence clearly shows that females are unconcerned with the effect of their behavior on males and do not structure their participation in homosexuality to maximize its impact on heterosexuality. Yet in spite of all this counterevidence, biologists still claim that a primary “function” of homosexual activity in females is to arouse males: “The sight of one female mounting another is said to excite males sexually in Squirrel monkeys and it may do so to males of other species too, for example men watching pornographic films of lesbian activity.”⁶³ By drawing an explicit parallel to human sexuality, the author of this statement hopes to argue for the evolutionary “usefulness” of homosexuality—but the analogy actually highlights the fundamental absurdity of this “explanation,” as well as its dependence on cultural rather than biological factors. True, many heterosexual men are aroused by the sight of two women having sex together, and lesbian sexuality is often packaged and trivialized as pornography to be consumed by straight men. But it would be ridiculous to conclude, on the basis of this, that lesbians have sex “in order” to arouse heterosexual men—yet this is exactly the type of reductionist thinking that is routinely applied to homosexual behavior in animals. It is also highly revealing that homosexual behavior among male animals is virtually never described as being stimulating for females.⁶⁴

Perhaps the most widespread version of the idea that homosexuality is really just a form of reproductive behavior concerns same-sex pairing in birds. It is frequently asserted that the “function” of such associations is to allow females to successfully raise young when they are unable to obtain a male mate. Not only is the initial premise of this explanation—that homosexual pairs result from the unavailability of members of the opposite sex— incorrect, but first and foremost, birds do not usually form same-sex pairs specifically to undertake parenting.⁶⁵ Species in which homosexual pairs never attempt to raise young are nearly as common as those in which same-sex parenting does occur. Even in those species where female pairs lay eggs, the proportion of their eggs that are actually fertile is usually low, indicating that the females do not mate with males or “try” to raise a family—fertil—ity rates as low as 0 percent for Kittiwakes, 0–15 percent for Western Gulls, 4–30 percent in Herring Gulls, 33 percent for Silver Gulls, and 8 percent in some populations of Ring-billed Gulls have been documented.⁶⁶ In addition, female pairs whose clutches are entirely infertile have been reported for Mute Swans, Black-winged Stilts, Roseate Terns, Blue Tits, Red-backed Shrikes, King and Gentoo Penguins, and Lovebirds (among others). Female Jackdaws who have lost their male partners sometimes pair up with nonbreeding females. However, these associations develop regardless of whether the widow has young, demonstrating that females do not form same-sex associations solely for the purpose of obtaining help in raising offspring. Moreover, only 10 percent of widowed females are involved in homosexual pairs, so even if such partnerships were “reproductively” motivated, it remains to be explained why only some females take advantage of such alternative parenting arrangements.

Nests belonging to homosexual pairs of Black-winged Stilts (left) and Red-backed Shrikes (right). Both females in the pair lay eggs, and therefore their nests contain “supernormal clutches” (double the usual number of eggs). Because neither female has mated with males, however, these clutches typically consist entirely of unfertilized eggs.

Furthermore, there are several different forms of same-sex parenting among birds (and other animals). In some cases, individuals develop full pair-bonds with their coparent, including courtship and sexual activity, and the partnership typically exists prior to and extends beyond the duration of parenting (e.g., Western Gulls, Black-winged Stilts). In other species, partners who already have offspring simply enter into a joint-parenting arrangement with no associated courtship or sexual activity between them, often lasting only until the young have been raised (e.g., Lesser Scaup Ducks). In still other cases, animals develop an intermediate arrangement, with “platonic” coparenting between individuals who may nevertheless continue to associate together even when not breeding (e.g., Acorn Woodpeckers, Squirrel Monkeys). And finally, in many species (e.g., Greylag Geese, Oystercatchers), individuals form bisexual trios that parent their offspring together (often contrasting with heterosexual trios and/or homosexual pairs within the same species).⁶⁷ All four types of arrangement could be interpreted as “strategies” to raise young, yet the differences between them remain unaddressed if homosexual associations are seen strictly as coparenting arrangements.

The putative benefits of same-sex breeding associations are also generally belied by the fact that not many individuals take advantage of them. The proportion of birds who participate in homosexual pairings or joint parenting arrangements is often relatively small—much smaller, in fact, than would be expected if this were simply an efficient or beneficial reproductive strategy. For example, most male Greater Rheas and Emus raise their young as single parents, but occasionally two males join forces, incubating their eggs in tandem and raising their chicks together. Single parenting can be taxing in these species—partnerless males, for instance, may fast during the entire incubation period, and single Greater Rhea fathers often lose eggs because they can’t keep large clutches warm—so it has been suggested that two males may be better equipped to handle the difficulties of parenting by helping each other. However, only a small fraction of nests are tended by two males (less than 3 percent in Greater Rheas): if this were truly a useful parenting strategy, why wouldn’t all males—or at least a larger proportion—be