Biological Exuberance: Animal Homosexuality and Natural Diversity

almost all “unfaithful” copulations occur outside the females’ fertilizable periods, while female Razorbills specifically avoid full genital contact during nonmonogamous matings until after fertilization is no longer possible.¹³⁷ Other, more complex arrangements are also found: the mating system of some species, such as Tasmanian Native Hens, is described as “social polygamy with genetic monogamy.” These birds live in polygamous groups, often several males mating with one female, but only one male fathers offspring with the female. This is the opposite of birds that form heterosexual pairs (“social monogamy”) but mate and produce offspring with other partners (“genetic polygamy”). In many species where individuals typically form pair-bonds, there is also usually a subset of individuals that form heterosexual trios.¹³⁸

Many pairing systems could probably be characterized as “serial monogamy.” Even in birds that tend to form lifelong pair-bonds, divorce occasionally happens, and in many species pairs break up much more frequently, individuals usually then remating with other partners.¹³⁹ In Oystercatchers, for instance, divorce and remating is quite common (especially among females), and some individuals have as many as six or seven consecutive mates over their lives. Overall divorce rates vary widely between different individuals and species, from 0 percent in Australian ravens and wandering albatrosses to about a quarter of Kittiwake, a third of natal robin, and two-thirds of Lapland longspur pairs, to nearly 100 percent of all pairs in house martins and Flamingos. Divorce may result from a failure to produce offspring, but in many cases a complex interaction of multiple factors is involved, including general partner incompatibility. Other types of heterosexual family breakup also occur: extended families in Ocellated Antbirds may disintegrate when male-female pairs leave or grandparents isolate themselves; Warthog family units composed of a male and a female with young are generally less stable than female-only families; yearling White-tailed Deer are usually driven away by their own mothers; and Snow Geese family units may break up prematurely when juveniles leave.¹⁴⁰

Heterosexual mating and parenting arrangements come in a staggering variety of forms—it is simply not the case that one type of “family” configuration is utilized by all species, or even by all individuals within the same species, or by the same individual for all of his or her life. Animal heterosexuality (like homosexuality) is a truly multidimensional, polymorphous phenomenon.

Sex without Purpose: Pleasure and Nonreproduction

Suzie stood with her back to Unk and she leaned her upper torso downward. He proceeded to manipulate her genitalia. That same day, … Suzie allowed subadult Smitty to lick her clitoris … . Observations … indicated that Suzie may experience orgasm … a shudder coursed through her entire body and then she became rigid.

—GREYSOLYNNE J. FOX, Social Dynamics in Siamang¹⁴¹

Even when males and females can overcome the considerable hurdles standing in the way of mating, they often engage in sexual activities that do not lead to reproduction. Several different forms of such “purposeless” sexual behavior can be identified, the most common being heterosexual sex that involves partners or situations where fertilization is impossible. As previously mentioned, many animals routinely mate (or engage in other sexual activities) outside of the breeding season or when the female is not ovulating—including during menstruation and pregnancy (or, in birds, during the incubation period). Not only is this found in a wide variety of animals—in mammals, for example, among various primates, hoofed mammals, carnivores, marsupials, rodents, and so on—but such nonprocreative sexual activity frequently constitutes a significant portion of all sexual behavior. In Common Murres, for instance, about half of all copulations in some populations occur during times when fertilization is not possible, while in Proboscis Monkeys and golden lion tamarins, a peak in sexual activity often occurs during pregnancy. ¹⁴² About half of all pregnant or menstruating Rhesus Macaques are sexually active, and some males mate with pregnant females as often as they do with ovulating females. In fact, sexual activity sometimes occurs during or shortly after birth in this species: males have been observed mounting females who just gave birth, while female attendants occasionally masturbate themselves while watching a female in labor. The birth process itself also stimulates sexual interest (courtship, mounting) in several species of hoofed mammals, including Mountain Goats, addax antelopes, and wildebeest.¹⁴³ In none of these cases can the “function” of such sexual activity be procreation. Heterosexual behavior also occurs among sexually immature animals, between adults and juveniles, between genetically related animals, between members of different species, and sometimes even between live and dead animals—all instances in which reproduction is not optimized (if not altogether impossible).¹⁴⁴

Multiple copulations—in which animals mate far in excess of the amount required for fertilization—are also widespread. Several species of wild cats and birds of prey, for instance, have astonishingly high copulation rates. Lions may mate up to 100 times a day during the breeding season (or as much as 1,500 times for each litter produced), while heterosexual pairs of goshawks and American kestrels mate 500-700 times for each clutch of eggs they produce.¹⁴⁵ Oystercatcher pairs also copulate about 700 times each breeding season, while female Kob antelopes may each experience several hundred heterosexual mounts during a 24-hour visit to the mating grounds.¹⁴⁶ In addition, animals of some species (e.g., Spinner Dolphins, Gray and Bowhead Whales, Herons, Swallows) engage in group sexual activity in which only a small subset of the participants (if any) are actually passing on their genes and reproducing.

Specific nonprocreative heterosexual practices in the animal world are many and varied, and they often parallel homosexual behaviors as well as the wide variety of nonreproductive sexual practices found in humans. To begin with, mounting that does not involve full genital contact—sometimes described as “symbolic,” “display,” or “noncopulatory” mounting—is widespread. For every “full” copulation in Kob antelopes, for instance, an average of three mounts without erection and six mounts with an erection but no penetration are performed by the male.¹⁴⁷ Reverse mounting—in which the female mounts the male, usually without mutual genital contact—also occurs in a wide variety of species, and sometimes involves “reciprocal” mounting or sequential exchange of positions between the male and the female. ¹⁴⁸ In some species, males occasionally mount females from the side or in other positions that do not involve penetration or genital contact: for example, Japanese Macaques, Waterbuck, Mountain Sheep, Takhi, Collared Peccaries, Warthogs, Koalas, Ruffs, Hammerheads, and Chaffinches. Many other types of nonprocreative sexual acts occur in mammals: various forms of oral sex (including fellatio, genital licking, and beak-genital propulsion); stimulation of a partner’s genitals with the hands or other appendages (such as flippers), including vaginal penetration with the fingers (in primates); anal stimulation, including penetration with fingers or oral-anal contact (e.g., Orang-utans), rump rubbing (e.g., in Bonobos and Common Chimpanzees), and even heterosexual anal intercourse (e.g., in Orang-utans).

Masturbation also occurs widely among animals, both male and female. A variety of creative techniques are used, including genital stimulation using the hand or front paw (primates, Lions), foot (Vampire Bats, primates), flipper (Walruses), or tail (Savanna Baboons), sometimes accompanied by stimulation of the nipples (Rhesus Macaques, Bonobos); auto-fellatio, or licking, sucking, and/or nuzzling by a male of his own penis (Common Chimpanzees, Savanna Baboons, Vervet Monkeys, Squirrel Monkeys, Thinhorn Sheep, Bharal, Aoudad, Dwarf Cavies); stimulation of the penis by flipping or rubbing it against the belly or in its own sheath (White-tailed and Mule Deer, Zebras, and Takhi); spontaneous ejaculations (Mountain Sheep, Warthogs, Spotted Hyenas); and stimulation of the genitals using inanimate objects (found in several primates and cetaceans; see chapter 2 for further discussion). Many birds masturbate by mounting and copulating with tufts of grass, leaves, or mounds of earth, and some mammals such as primates and Dolphins also rub their genitals against the ground or other surfaces to stimulate themselves. One fairly unusual form of (indirect) genital stimulation occurs in some hoofed mammals. Among male Red Deer, Moose, Wapiti, and other species of Deer, the antlers are erotic organs that can result in sexual arousal and even ejaculation when they are rubbed. In addition to occasionally stimulating each other this way, males of these species often stimulate themselves by rubbing their antlers in clumps of vegetation.¹⁴⁹

Sex for pleasure: masturbation in a male Walrus (left) and a White- tailed Deer

Masturbation in female mammals, as well as heterosexual and homosexual intercourse (especially in primates), often involves direct or indirect stimulation of the clitoris (as in the description at the beginning of this