using it? Clearly something more—or something else—is involved in associations between males than simply the parenting benefits they may accrue. To further confound the picture, in Greater Rheas both same-sex coparenting and same-sex nest helpers occur. While some males jointly parent the same brood of young, a much higher percentage (about a quarter, still a minority of the population) are assisted by an adolescent male who separately parents one of their nests. Once again, this raises the question of why some males opt for joint parenting, others “choose” to have male helpers, while most do neither. And in many species the supposed advantages of coparenting as opposed to single parenting are in fact illusory. Most female Lesser Scaups raise their young with no help from males, but occasionally two or three females coparent. It is usually assumed that this strategy gives such females an advantage in parenting, but detailed studies of parental investment have shown that same-sex coparents are no more and no less successful than single parents. Moreover, each female in such an arrangement generally spends the same amount of time in parenting duties as do single females, i.e., she is not “relieved” of some of her responsibilities by her companion. In other words, there is essentially no reproductive advantage to joining forces with a parenting partner in this species.68
Nor is the occurrence of homosexual pairing in other species correlated with the supposed advantages of having an opposite-sex partner to help with parenting. Even in birds where male-female coparenting is typical, there are often significant differences between species in how essential that biparental care is to successful chick-raising. In some birds, females can raise young without the assistance of a male partner, while in other species the male’s contribution is indispensable. If homosexual pairing were somehow related to the (in)ability of single birds to raise young on their own, one would expect same-sex associations to occur in species where biparental care is more important, i.e., where single birds cannot raise young on their own—yet the facts do not support this. Consider two parallel examples: Snow Geese and Black-billed Magpies. Homosexual pairing in female Snow Geese is claimed to allow otherwise single birds to raise young. However, biparental care is not essential for successful reproduction in this species: when females in heterosexual pairs have their male partners taken away from them, they are quite capable of raising their young as single parents. On the other hand, biparental care is essential in Black-billed Magpies, since females are unable to raise offspring on their own when they lose (or are deprived of) their male mates. Yet homosexual pairs of Magpies do not raise young together, nor do widowed females form same-sex pairs in this species (unlike the closely related Jackdaws). This is exactly the opposite of what would be expected if mateless birds were forming homosexual associations to enable them to parent.69
In fact, most pair-bonding birds do not form same-sex couples when heterosexual mates desert them or are experimentally removed, indicating that homosexual pairing is not a widespread mechanism for achieving two- parent care (regardless of whether the latter is “indispensable” or simply preferred). Moreover, in those polygamous (non-pair-bonding) species such as the Superb Lyrebird where females could benefit significantly from male parental assistance (and appear to suffer detrimental effects in its absence, such as slowed growth of their offspring), female pairing and coparenting is noticeably absent.70 Conversely, same-sex pairing and/or coparenting do occur in many species where single parents routinely raise young successfully. This is true for Hooded Warblers and Mallards (where heterosexual parents almost always separate and become single parents before the young are fledged), and Red Squirrels and Grizzlies (where heterosexual coparenting never occurs as part of these species’ polygamous mating systems). In none of these animals is a two-parent family (either heterosexual or homosexual) absolutely required for successful parenting.
To take this line of thinking a step further: in a few species homosexual associations may actually be detrimental to parenting. Besides providing no apparent parental benefits to each other, Calfbird female companions may in fact increase their risk of predator attacks by nesting so close to each other (thereby drawing attention to their location). Female Japanese Macaques in homosexual consortships also do not typically assist their partner with parenting and are often notably aggressive toward their consort’s offspring. Homosexual bonding is reproductively disadvantageous for both Oystercatchers and Jackdaws in bisexual trios, for slightly different reasons. Oystercatchers in such associations typically do not jointly incubate their supernormal clutches (only one bird sits on the nest at a time); because each incubator is unable to cover all the eggs simultaneously, the outsized clutch is often not kept adequately warm. As a result, bisexual trio parents hatch fewer eggs and produce significantly fewer fledglings than heterosexually paired Oystercatchers. Female Jackdaws in bisexual trios, on the other hand, do jointly incubate their supernormal clutches. However, because the two females are bonded to each other, both leave the nest together when their male partner arrives to relieve them, and he is unable to cover all their eggs and keep them warm. A parallel effect may occur in Lesser Scaup Ducks: although most female coparents exhibit remarkable cooperative defense of their joint broods, some pairs have been observed flying off together at the approach of a predator, temporarily abandoning their young in the face of danger. Finally, female Canada Geese in homosexual pairs sometimes roll eggs between their adjacent nests, breaking many of them in the process.71 Clearly, then, successful parenting—and, by extension, reproduction or “perpetuation of the species”—cannot be the whole story behind the formation of same-sex pair-bonds.
Sperm-Swapping and Other Flights of Fancy
Attempts to determine the evolutionary “function” of homosexuality have sometimes led to even more obscure and implausible “explanations,” all revolving (predictably) around heterosexual breeding. For example, some scientists have suggested that homosexuality is a form of reproductive “competition”: females have sex (or form pair-bonds) with other females to monopolize their partner’s time and thereby prevent her from mating heterosexually, while males mount each other to reduce or redirect their rival’s sexual drive.72 However, in many species homosexual interactions are actively initiated by the animals who are mounted rather than by the mounters, and the participants often have a friendly rather than a competitive relationship with each other.73 Moreover, there is no evidence that participation in homosexual mounting reduces heterosexual activity—indeed, in some species the opposite is true, for the greatest amount of heterosexual mating is accomplished by precisely those individuals who are also the most active homosexually (as discussed previously). And, as already mentioned, in many animals homosexual activity does not even take place during the breeding season or is only exhibited by a small proportion of individuals.
Another version of this competition hypothesis is that homosexuality is a way of directly interfering with the heterosexual activity of a rival. In a number of birds—Pukeko, Guianan Cock-of-the-Rock, Ocher-bellied Flycatchers, and Buff-breasted Sandpipers—homosexual activity is claimed to be a form of “disruption” whereby one male prevents another from mating with a female, while possibly also “usurping” his partner and mating heterosexually himself. The specifics of same-sex courtship and mating in each case, however, do not support this interpretation. In Pukeko, for example, males do sometimes interrupt heterosexual mating attempts by inviting the other male to mount them, but they do not generally take advantage of the situation to mate with the female partner. Moreover, this occurs only infrequently, and males are more likely to ignore heterosexual matings by other males or watch them without interfering than they are to try to prevent them from occurring. In addition, even if a male were trying to use homosexuality as a way to disrupt a heterosexual mating, this strategy would not “work” unless the other male found the prospect of mounting him more appealing than completing his heterosexual copulation. Ironically, then, a “disruption” interpretation of same-sex mounting in this species—typically presented as an example of the primacy of heterosexual relations—actually entails the assumption that male Pukeko would prefer homosexual activity. In Ocher-bellied Flycatchers, the suggestion that males are trying to disrupt heterosexual matings, or to gain access to females, is entirely speculative. Males have never been seen mating with a female as a result of a homosexual interaction in this species, and in fact females are not even present during the majority of courtship pursuits between males. Homosexual activity is also classified as a form of courtship “disruption” in the Guianan Cock-of-the-Rock, yet there is little evidence in favor of this explanation. As much, if not more, homosexual activity takes place when females are not present on the male’s display territories, and males who initiate such “disruptions” almost never gain access to members of the opposite sex as a result and have rarely even been observed mating with females. Furthermore, visits by yearling males involving homosexual activity are distinct from true courtship disruptions, which are performed by rival adult males. Yearling visits are directed toward a wide variety of males, all of whom cooperate in the interaction. In contrast, rival males target only the most successful heterosexual breeders and are violently attacked by the males they try to disrupt. In addition, same-sex interactions are sometimes directed toward adult nonbreeders, who do not participate in heterosexual mating at all, so it is difficult to see how this could be a form of
