sexual and related social behaviors with females.52
Homosexual activity in birds also generally fails to be correlated with patterns of exclusion from (or nonparticipation in) heterosexual mating. In Ruffs, for instance, mountings between males are actually more common when females are present on the breeding grounds than when they are absent. Even though males sometimes do try to prevent each other from mating heterosexually, same-sex mounts are not simply “redirected” or “substitute” heterosexual copulations. Homosexual mounts occur among a variety of different classes of males even when they are not directly “prevented” from mating with females (such as individuals known as satellites and naked-nape males). Conversely, one class of males—so-called marginal males—that is routinely excluded from opposite-sex interactions (by direct attacks from other males) does not usually engage in homosexual activity either. In Pukeko, a significant portion of the population assists other birds in raising their young rather than breeding themselves; however, homosexual activity in this species is characteristic of breeding individuals rather than such nonbreeding “helpers.” In Ocher-bellied Flycatcher and Ruffed Grouse populations that have a “surplus” of nonbreeding birds, breeding territories often go unused, indicating that nonbreeders are not being “prevented” from mating heterosexually (or at least are choosing to remain nonbreeders until better territories become available). Moreover, only a portion of such nonbreeders ever participate in same-sex activity, which in these species generally involves at least one partner that does have his own breeding territory. Likewise, the incidence of homosexual bonding among Oystercatchers (in the form of bisexual trios) does not increase significantly under higher population densities, when many individuals are unable to acquire their own opposite-sex mates and breeding territories. Brown-headed Cowbird populations generally have a significant surplus of males, and higher-ranking males also actively prevent lower-ranking males from courting and pairing with females. Yet the large number of birds thereby “excluded” from heterosexual mating opportunities—half to two-thirds of all males—do not regularly court or mate with one another. In fact, the only homosexual activity observed in this species involves male Cowbirds occasionally being mounted by males of another species, House Sparrows. Finally, Guianan Cock-of-the-Rock exhibit a pattern of homosexual and heterosexual participation that is strikingly similar to that of American Bison. Both yearling and two-year-old males are generally “excluded” from breeding, yet extensive homosexual activity only occurs in the former age group—and almost always with adult males as partners, many of whom are not excluded from heterosexual mating.53
Homosexuality is not generally the result of animals being “deprived” of heterosexual mating opportunities— this can be seen quite clearly in the behavior of individuals toward members of the opposite sex in skewed or segregated populations (in both the wild and captivity). Potential heterosexual partners are often ignored or even actively refused in such situations—they are rarely inundated with attentions as would be expected if animals were being excluded from participation in opposite-sex mating. In Giraffe populations with a majority of males, for instance, females are not swamped with heterosexual attentions, and mating opportunities with females are sometimes even bypassed in favor of homosexual mounting and other activities. Female Japanese Macaques and Hanuman Langurs engaging in homosexual activities usually disregard males entirely and may actually threaten or attack them if they make sexual overtures. Gray Seal and Killer Whale homosexual activities usually take place in all-male groups; although a few females are occasionally present in such groups, they are subject to little sexual attention from the males, the majority of whom ignore them altogether. This is in stark contrast to the often violent sexual attacks by large numbers of males on females during the breeding season in Gray (and other) Seals. Female Plains and Mountain Zebras living alone or in “bachelor” (or nonbreeding) herds are rarely approached sexually (or competed for) by either “bachelor” males or herd stallions (both of whom sometimes participate in homosexual activities). Stallions may even actively prevent new females from joining their herds. “Surplus” male Great Cormorants—some of whom form homosexual pairs—never display any interest in the (heterosexually paired) females among them. Conversely, in populations of Orange-fronted Parakeets with an “excess” of females, homosexual pairing is not limited to birds that “can’t find” heterosexual mates, since females paired with males also regularly form same-sex bonds (as part of bisexual trios). Adult bull Wapiti often show no sexual interest in females they happen to encounter outside the breeding season (even if the females are in heat at that time), while younger bulls do often show such interest. Yet homosexual activity in this species occurs in both age groups outside the breeding season—and therefore in neither case can it be due to a lack of access to females. Finally, in many Duck species that have a surplus of males, females are swamped by males trying to rape them—but in almost all cases, such males are already paired to females. Unpaired males without access to heterosexual partners rarely, if ever, engage in forced copulations with females (regardless of whether homosexual behavior also occurs in the species).54
A herd of male Gray Seals hauled out on land during the molting period on Ramsay Island (England). Just before this picture was taken, the two bulls at the water’s edge near the large rock were engaging in homosexual activity-a common pursuit among males of all ages at this time of year. Although a few females may be present in these spring haul-outs, they are largely ignored by the males, demonstrating that their homosexual activity is not simply a “substitute” for heterosexual mating.
Even same-sex activity that does have its genesis in the absence of opposite-sex partners—so called situational homosexuality—often shows remarkable longevity and durability, rarely conforming to the stereotype of being “fragile” or liable to disintegrate once heterosexual mates are available. Captive animals that bond sexually with one another when opposite-sex partners are completely unavailable often resist later attempts to “convert” them to heterosexuality. They may even exhibit a longer-term “preference” for same-sex mates that outlasts their initial “situational” introduction to homosexuality. A pair of male White-fronted Amazon Parrots, for example, vigorously refused the advances of female birds even though their homosexual bond was formed “because” no females were available, while two female Long-eared Hedgehogs who were sexually involved with each other in the absence of males refused to mate heterosexually for up to two and a half years after they were separated (as mentioned earlier). The bonding in same-sex pairs of male Steller’s Sea Eagles and female Barn Owls (housed without any heterosexual mates) was strong enough to enable successful coparenting of chicks, and in some cases the birds ignored subsequent introductions of opposite-sex partners. Male Rhesus Macaques, Crab- eating Macaques, Bottlenose Dolphins, Cheetahs, and Black-headed Gulls with homosexual bonds resist the attentions of opposite-sex partners or are clearly distressed when separated from one another, and/or they promptly renew their relationship on being reunited—often showing visible signs of affection and excitement when seeing their male partner again. This is also true for male Mallard Ducks that are raised together, in whom homosexual pairing typically becomes their lifetime “orientation.” They consistently seek the company of other males even when opposite-sex mates are available and maintain their homosexual bonds year after year (or re-pair with males after the death of a partner) in spite of persistent overtures from females.55
The Contamination of Homosexuality
Of all the scientists who have advocated a shortage explanation for homosexuality, not one has ever specified a critical sex ratio that will consistently “induce” homosexuality, or a crucial threshold of members of the opposite sex that must be present in order to unfailingly prevent individuals from “resorting” to homosexuality. Is a mere 5 percent surplus of one sex enough to tip the scales? Apparently, since a population of Ring-billed Gulls with only 55 percent females is claimed to have enough of a skew to “cause” homosexual pairing. Yet a 5 percent excess of males in other species such as Greylag Geese is apparently not sufficient to “precipitate” homosexual pairing.56 In fact, it is highly unlikely that a single critical sex ratio could ever be specified, because the proportion that “causes” homosexuality in one species (or population) has no such effect at all in other species, even where enormous “surpluses” (of, say, 80 percent or more of one sex) are concerned. More broadly, the underlying assumption behind the shortage hypothesis—that sex ratios actually determine a species’ mating habits and social systems—has already been shown to be false for other types of mating behaviors. Scientists now recognize that there is not a clear, one-way causal relationship between how many males or females are available in a population, and the form that their mating system takes (e.g., polygamy as opposed to monogamy). Rather, a complex interplay of many factors is at work.57 Unfortunately, the subtlety of this interaction is generally only recognized where heterosexual mating systems are concerned.
The shortage hypothesis is not only suspect on theoretical grounds, it is often applied to particular cases in a
