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{269} Mammals
Primates
      APES
Great Apes
      BONOBO or PYGMY CHIMPANZEE (Pan paniscus)
IDENTIFICATION: Similar to the Common Chimpanzee, but more slender and with longer limbs, a uniformly dark face, and a slight "part" in the hair on top of the head. DISTRIBUTION: Central and western Congo (Zaire); endangered. HABITAT: Tropical lowland rain forest. STUDY AREAS: Wamba and the Lomako Forest, Congo (Zaire); Yerkes Regional Primate Research Center (Georgia); San Diego Zoo; Wild Animal Park (San Diego); Frankfurt and Stuttgart Zoos, Germany.

     
Two female Bonobos participating in "GG (genito-genital) rubbing"

      Social Organization
      Bonobos live in communities composed of large mixed-sex and mixed-age groups containing up to 60 or more individuals. These often divide into smaller, temporary subgroups that have a more fluid membership. On reaching adolescence (and becoming sexually mature), female Bonobos typically leave their home group and emigrate to a new one, while males usually remain in their home group for life. Females often form strongly bonded subgroups and are generally dominant to males. The mating system is promiscuous: males and females mate with multiple partners, and males do not generally participate extensively in raising their offspring.


Two female Bonobos in Congo (Zaire) "GG (genito-genital) rubbing"

      Description
      Behavioral Expression: Bonobos have one of the most varied and extensive repertoires of homosexual practices found in any animal. Females engage in an extraordinary form of mutual genital stimulation that, in many aspects, is unique to this species. Sometimes known as GG-RUBBING (for genito-genital rubbing), this behavior is usually performed in a face-to-face embracing position (heterosexual copulation is also sometimes done in this position, but not as often as in lesbian {270} interactions). One female stands on all fours and literally "carries" or lifts her partner off the ground; the female on the bottom wraps her legs around the other's waist and clings to her as they rapidly rub their genitals against one another, directly stimulating each other's clitoris. Some scientists believe that the particular shape and location of the Bonobo's genitals have evolved specifically for lesbian rather than heterosexual interactions. During GG-rubbing, each female rhythmically swings her pelvis from side to side — precisely timed so that each partner is thrusting in opposite directions — at a rate of about two thrusts per second. This is comparable to the thrusting rate seen in males during heterosexual interactions, but males thrust vertically rather than sideways. In addition, although both homosexual and heterosexual copulations are quite brief, same-sex interactions generally last slightly longer — an average of about 15 seconds (maximum of 1 minute) compared to about 12 seconds (maximum of 45 seconds) for heterosexual matings. Sometimes females GG-rub with the same partner several times in a row.
      As shown by their facial expressions, vocalizations, and genital engorgement, females experience intense pleasure — and probably orgasm — during homosexual interactions. Partners gaze intensely into each other's eyes and maintain eye contact throughout the interaction. Sometimes, females grimace or "grin" by baring their teeth wide and also utter screams or squeals that are thought to be associated with sexual climax. The Bonobo's clitoris is prominent and well-developed; during sexual arousal it undergoes a full erection of both the shaft and glans (in humans, only the glans of the clitoris becomes enlarged), swelling to nearly twice its regular size. Remarkably, clitoral penetration has occasionally been observed between females during homosexual interactions {271} (in captivity). When penetration occurs, the females often switch to vertical thrusting (as in heterosexual mating) rather than the usual sideways hip movements.
      Genital stimulation between females is sometimes performed in different positions: the two partners may both hang from a branch facing each other; one female may mount the other from behind; one female might lie on her back while the other stands facing away from her, rubbing her genitals on her recumbent partner's vulva; or both females may lie on their backs or stand rump-to-rump while GG-rubbing. In the face-to-face position, females may alternate between who is on bottom and who is on top; prior to interacting, they often "negotiate" positions by lying down with legs spread to see whether the other partner wants to be on top. GG-rubbing occurs among females of all ages, from adolescent to very old, but if an older and a younger female are interacting, often the younger female will be on top. Sexual activity may also be more common when the females are of different ranks. Homosexual interactions are often initiated with a characteristic series of "courtship" signals: approaching the partner and peering closely, standing on the hind legs and raising the arms over the head while making eye contact, and/or touching the shoulder or knee while staring. Among captive Bonobos, partners may also use a highly developed "lexicon" of manual gestures to help negotiate the position(s) to be used in sexual interactions (see pp. 66-69 for more detailed discussion).
      Females may have multiple sexual partners. In one troop containing ten females, each female interacted sexually with five other females on average, and some had as many as nine different partners. Group sexual activity also occasionally takes place, with three to five females simultaneously rubbing their genitals together. Some females are considered especially {272} "attractive" — usually because of the shape, size, and coloration of their genital swellings — and individuals may have preferred partners that they tend to interact with more often. In fact, females typically form strongly bonded, enduring relationships with one another that are fostered by sexual interactions and include such activities as mutual grooming, play, food-sharing, and alliance-formation (often for challenging males). Females generally prefer each other's company, and their same-sex bonds form the core of social organization. In addition, when new females (usually adolescents) join a troop, they often pair up with an older female with whom they have most of their sexual and affectionate interactions. These bonds need not be exclusive — either party may have sex with other females or males — but such mentorlike pairings can last for a year or more until the newcomer is fully integrated into the troop. In this species, a sort of homosexual "incest taboo" is in effect for these pair-bonds: most females are unrelated to the Bonobos in their new troop, but those who are related are not chosen as special partners. Some homosexual activity does, however, occur between mothers and their daughters.
      Male Bonobos also have a wide variety of homosexual interactions. Sometimes, two males mutually stimulate each other's genitals using a face-to-face position similar to GG-rubbing: one male lies on his back and spreads his legs while the other thrusts on him, rubbing their erections together (in this and all other male homosexual activity, anal penetration is not involved). If there is an age difference between partners, often the younger male will be on the bottom. Occasionally, two males hang from a branch facing each other and engage in what is known as PENIS FENCING, swinging their hips from side to side as they rub their erect penises on each other or cross them as if they were fencing with swords. Another activity is RUMP RUBBING, in which two males stand on all fours in opposite directions, pressing their buttocks against each other and mutually rubbing their anal and scrotal regions. Both males often have erections. Males also mount each other from behind and either mountee or mounter may make thrusting movements. Sometimes the males switch positions, and the mounter may scream or grin in sexual arousal as in lesbian or heterosexual interactions. Bonobo males have also been seen standing on their hind legs, one embracing the other from behind. Other sexual activities include oral sex, or fellatio, in which one male sucks another's penis at the initiation of either partner (usually seen only in younger males). Manual stimulation of the {273} genitals by a partner also occurs: typically an adolescent male spreads his legs and presents his erect penis to an adult male, who takes the shaft in his hand and caresses it with up-and-down movements. Younger males (and occasionally females) also sometimes give each other openmouthed kisses, often with extensive mutual tongue stimulation. Although males do not appear to form pairlike bonds with sexual partners (as do some females), occasionally two or three males are intimately associated as companions, constantly accompanying each other and foraging together.

   
A male Bonobo mounting another male from behind

      Frequency: Homosexual activity is nearly as common as heterosexual activity in Bonobos, accounting for 40-50 percent of all sexual interactions; two-thirds to three-quarters of this same-sex activity is between females (mostly GG-rubbing). Daily life among Bonobos is characterized by numerous relatively brief episodes of sexual activity scattered throughout the day, and homosexual interactions are frequent. Each female participates in GG-rubbing on average once every two hours or so, and some newcomers to a troop do so even more often, on an hourly basis.


Two younger male Bonobos engaging in fellatio

      Orientation: Virtually all Bonobos are bisexual, interacting sexually with both males and females. In fact, motherhood and homosexual activity are fully integrated among Bonobos, as a female often GG-rubs with another female while her infant is clinging to her belly. Usually same-sex and opposite-sex activities are interspersed or alternated, although both may occur simultaneously during group sexual interactions. Nevertheless, it appears that — among some females at least — homosexual activity is preferred. Although females vary along a continuum, with one-third to nearly 90 percent of their interactions being with partners of the same sex, overall there is often a predominance of homosexual activity. An average of two-thirds of all sexual interactions among females are with other females, and individuals generally have more female than male sexual partners. In addition, females have sometimes been observed consistently ignoring males who are soliciting them for sex, preferring instead to GG-rub with each other.

     
An adult male Bonobo (left) manually stimulating the penis of a younger male

      Nonreproductive and Alternative Heterosexualities
      Variety, flexibility, and frequency of sexual interactions are not limited to contact between Bonobos of the same sex — heterosexual activity is replete with nonreproductive behaviors. Rump rubbing, fellatio, and manual stimulation of the genitals by either sex (including fondling of the scrotum) are all aspects of male-female sexual interactions. In addition, females occasionally mount males from behind (REVERSE mounts), and heterosexual copulation often does not involve penetration and/or ejaculation, but simply mutual rubbing of genitals. Both male and female Bonobos also masturbate (males sometimes using inanimate objects to stimulate themselves). Group sexual activity occurs as well, often with one individual thrusting against a pair who are copulating, and individuals may participate in several bouts of heterosexual activity in rapid succession. Sometimes, because of the frequency and persistence of sexual invitations — often associated with begging for food — individuals (especially males) may even become annoyed and try to avoid {274} further heterosexual interaction. In addition, females occasionally cooperate with one another in harassing and attacking males, in some cases causing severe injuries by holding a male down and biting his ears, fingers, toes, or genitals.
      Bonobos mate during all phases of a female's sexual cycle, and about a third of copulations occur during periods when fertilization is unlikely or impossible. Mating also takes place during pregnancy, sometimes as late as one month before delivery. Both adult males and females interact sexually with adolescents and juveniles (three-to-nine-year-olds). In fact, young females go through a five-to-six-year period sometimes referred to as ADOLESCENT STERILITY (although no pathology is involved) during which they actively participate in heterosexual mating (often with adults) but never get pregnant. Sexual behavior between adults and infants of both sexes is also common — about a third of the time it is initiated by the infant and may involve genital rubbing and full copulatory postures (including penetration of an adult female by a male infant). Another form of nonreproductive sexuality involves contact with other species: younger male Bonobos have occasionally been observed engaging in playful sexual interactions with redtail monkeys (Cercopithecus ascanius) in the wild.


Two male Bonobos "rump rubbing"

      Sources (* asterisked references discuss homosexuality/transgender)
      * Blount, B. G. (1990) "Issues in Bonobo (Pan paniscus) Sexual Behavior." American Anthropologist 92: 702-14.
      * Enomoto, T. (1990) "Social Play and Sexual Behavior of the Bonobo (Pan paniscus) With Special Reference to Flexibility." Primates 31:469-80.
      * Furuichi, T. (1989) "Social Interactions and the Life History of Female Pan paniscus in Wamba, Zaire." International Journal of Primatology 10:173-97.
      * Hashimoto, C. (1997) "Context and Development of Sexual Behavior of Wild Bonobos (Pan paniscus) at Wamba, Zaire." International Journal of Primatology 18:1-21.
      * Hashimoto, C., T. Furuichi, and O. Takenaka (1996) "Matrilineal Kin Relationships and Social Behavior of Wild Bonobos (Pan paniscus): Sequencing the D-loop Region of Mitochondrial DNA." Primates 37:305-18.
      * Hohmann, G. and B. Fruth (1997) "The Function of Genito-Genital Contacts among Female Bonobos (Pan paniscus)." In M. Taborsky and B. Taborsky, eds., Contributions to the XXV International Ethological Conference, p. 112. Advances in Ethology no. 32. Berlin: Blackwell Wissenschafts-Verlag.
      * Idani, G. (1991) "Social Relationships Between Immigrant and Resident Bonobo (Pan paniscus) Females at Wamba." Folia Primatologica 57:83-95.
      * Kano, T. (1992) The Last Ape: Pygmy Chimpanzee Behavior and Ecology. Stanford: Stanford University Press. Translated from the Japanese by Evelyn Ono Vineberg.
      * --- (1990) "The Bonobos' Peaceable Kingdom." Natural History 99(11):62-71.
      * --- (1989) "The Sexual Behavior of Pygmy Chimpanzees." In P. G. Heltne and L. A. Marquardt, eds., Understanding Chimpanzees, pp.176-83. Cambridge, Mass.: Harvard University Press.
      * --- (1980) "Social Behavior of Wild Pygmy Chimpanzees (Pan paniscus) of Wamba: A Preliminary Report." Journal of Human Evolution 9:243-60.
      * Kitamura, K. (1989) "Genito-Genital Contacts in the Pygmy Chimpanzee (Pan paniscus)." African Study Monographs 10:49-67.
      * Kuroda, S. (1984) "Interactions Over Food Among Pygmy Chimpanzees." In R. L. Susman, ed., The Pygmy Chimpanzee: Evolutionary Biology and Behavior, pp. 301-24. New York: Plenum Press.
      * --- (1980) "Social Behavior of Pygmy Chimpanzees." Primates 21:181-97.
      * Parish, A. R. (1996) "Female Relationships in Bonobos (Pan paniscus): Evidence for Bonding, Cooperation, and Female Dominance in a Male-Philopatric Species." Human Nature 7:61-96.
      * --- (1994) "Sex and Food Control in the 'Uncommon Chimpanzee': How Bonobo Females Overcome a Phylogenetic Legacy of Male Dominance." Ethology and Sociobiology 15:157-79.
      * Roth, R. R. (1995) "A Study of Gestural Communication During Sexual Behavior in Bonobos (Pan paniscus Schwartz)". Master's thesis, University of Calgary. {275}
      Sabater Pi, J., M. Bermejo, G. Illera, and J. J. Vea (1993) "Behavior of Bonobos (Pan paniscus) Following Their Capture of Monkeys in Zaire." International Journal of Primatology 14:797-804.
      * Savage, S. and R. Bakeman (1978) "Sexual Morphology and Behavior in Pan paniscus." In D. J. Chivers and J. Herbert, eds., Recent Advances in Primatology, vol. 1, pp. 613-16. New York: Academic Press.
      * Savage-Rumbaugh, E. S., and R. Lewin (1994) Kanzi: The Ape at the Brink of the Human Mind. New York: John Wiley & Sons.
      * Savage-Rumbaugh, E. S., and B. J. Wilkerson (1978) "Socio-sexual Behavior in Pan paniscus and Pan troglodytes. A Comparative Study." Journal of Human Evolution 7:327-44.
      * Savage-Rumbaugh, E. S., B. J. Wilkerson and R. Bakeman (1977) "Spontaneous Gestural Communication among Conspecifics in the Pygmy Chimpanzee (Pan paniscus)." In G. Bourne, ed., Progress in Ape Research, pp. 97-116. New York: Academic Press.
      * Takahata, Y., H. Ihobe, and G. Idani (1996) "Comparing Copulations of Chimpanzees and Bonobos: Do Females Exhibit Proceptivity or Receptivity?." In W. C. McGrew, L. F. Marchant, and T. Nishida, eds., Great Ape Societies, pp. 146-55. Cambridge: Cambridge University Press.
      Takeshita, H., and V. Walraven (1996) "A Comparative Study of the Variety and Complexity of Object Manipulation in Captive Chimpanzees (Pan troglodytes) and Bonobos (Pan paniscus)." Primates 37: 423-41.
      * Thompson-Handler, N., R. K. Malenky, and N. Badrian (1984) "Sexual Behavior of Pan paniscus Under Natural Conditions in the Lomako Forest, Equateur, Zaire." In R.L. Susman, ed., The Pygmy Chimpanzee: Evolutionary Biology and Behavior, pp. 347-68. New York: Plenum Press.
      * de Waal, F. B. M. (1997) Bonobo: The Forgotten Ape. Berkeley: University of California Press.
      * --- (1995) "Sex as an Alternative to Aggression in the Bonobo." In P. A. Abramson and S. D. Pinkerton, eds., Sexual Nature, Sexual Culture, pp. 37-56. Chicago: University of Chicago Press.
      * --- (1989a) Peacemaking Among Primates. Cambridge, Mass.: Harvard University Press.
      * --- (1989b) "Behavioral Contrasts Between Bonobo and Chimpanzee." In P. G. Heltne and L. A. Marquardt, eds., Understanding Chimpanzees, pp. 154-73. Cambridge, Mass.: Harvard University Press.
      * --- (1988) "The Communicative Repertoire of Captive Bonobos (Pan paniscus), Compared to That of Chimpanzees." Behavior 106:184-251.
      * --- (1987) "Tension Regulation and Nonreproductive Functions of Sex in Captive Bonobos (Pan paniscus)." National Geographic Research 3:318-35.
      Walraven, V., L. Van Elsacker, and R. F. Verheyen (1993) "Spontaneous Object Manipulation in Captive Bonobos." In L. Van Elsacker, ed., Bonobo Tidings: Jubilee Volume on the Occasion of the 150th Anniversary of the Royal Zoological Society of Antwerp, pp. 25-34. Leuven: Ceuterick Leuven.
      * White, F., and N. Thompson-Handler (1989) "Social and Ecological Correlates of Homosexual Behavior in Wild Pygmy Chimpanzees, Pan paniscus." American Journal of Primatology 18:170.
{276}
Great Apes
      COMMON CHIMPANZEE (Pan troglodytes)
IDENTIFICATION: The familiar small ape, with black, gray, or brownish fur, prominent ears, and variable facial coloring, from black to brown and pink (especially in younger animals). DISTRIBUTION: Western and central Africa, from southeastern Senegal to western Tanzania; endangered. HABITAT: Woodland savanna, grassland, tropical rain forest. STUDY AREAS: Mahale Mountains National Park and the Gombe Stream National Park, Tanzania; Budongo Forest, Uganda; eastern Congo (Zaire); Arnhem Zoo, the Netherlands; Anthropoid Station, Tenerife; Yale University Primate Laboratory and chimpanzee colony (New Haven, Conn., Franklin, N.H., and Orange Park, Fla.); ARL Chimpanzee Colony, N.Mex.; Delta Regional Primate Research Center, La.; subspecies P.t. schweinfurthii.

      Social Organization
      Common Chimpanzees live in groups or communities of 40-60 individuals, usually with twice as many adult females as males. Within each group, smaller subgroups often form, and some individuals form longer-lasting bonds with each other as part of a complex network of social and communicative interactions. The mating system is promiscuous or polygamous: males and females each mate with multiple partners, and males do not generally participate in raising their own offspring.


The kiss: two male Chimpanzees

      Description
      Behavioral Expression: Female Common Chimpanzees participate in a variety of same-sex activities. One form of mutual genital stimulation is sometimes known as BUMPRUMP: two females, standing on all fours and facing in opposite directions, rub their rumps together (usually in an up-and-down motion), stimulating their genital and anal regions. Sometimes one female lies on top of the other in a face-to-face position — or the two sit facing one another — rubbing their genitals together. Mounting also occurs in the front-to-back position typical of heterosexual mating. Unlike male-female mountings, though, the angle and position of the mounting female's body and arms may be slightly different from that of a male, her pelvic thrusts may be slower or more perfunctory, and she may rub against the other female's genitals with her belly rather than her own genital region. Occasionally female Chimps also engage in cunnilingus: one individual presents her {277} buttocks by crouching in front of the other, who stimulates her external genitalia with her lips and tongue.
      Among males, several different kinds of same-sex interactions occur. Manual contact or stimulation of a partner's genitals, for example, can involve fondling, rubbing, or gripping of the penis and/or touching of the scrotum, sometimes while the partner makes pelvic thrusts that "bounce" his genitals on his partner's hand. Chimps occasionally also engage in fellatio, mutual penis-rubbing while sitting face-to-face, mounting in a front-to-back position (sometimes with pelvic thrusts or body shaking), and even insertion of a finger into the partner's anus and oralanal "grooming" in a 69 position. A number of these activities — notably genital touching, mounting, and anal contact — occur as ritualized sexual gestures in the context of greeting, enlisting of support, reconciliation, and/or reassurance. They are often combined with affectionate gestures between males such as embracing, kissing (including openmouthed contact), grooming, and genital kissing or nuzzling. Males who participate in such activities may be bonded together in a mutually supportive "friendship" or COALITION. Occasionally male Chimpanzees also interact sexually with male Savanna Baboons in the wild. One adolescent Chimp, for example, was observed holding and fondling the penis of an adult male Baboon.
      Transgendered or intersexual Common Chimpanzees occasionally occur as well. One individual who was physically and anatomically a male was chromosomally a mosaic, combining both the male (XY) and the female (XX) chromosome types.

      Frequency: The prevalence of same-sex activities between male Common Chimpanzees is highly variable. Mounting between males constitutes anywhere from 1-2 percent to one-third or one-half of the behaviors involved in reassurance, enlistment of support, and other activities during or following conflicts. Kissing and embracing between males constitute from 12-30 percent of such interactions (depending on the population). Overall, 29-33 percent of all mounting activity occurs between males. Less detailed information is available for females, but a similar range of frequencies is probably involved. Other homosexual activities such as bumprump and oral or manual stimulation of genitals have so far been observed largely in captivity, where they may be fairly common.

      Orientation: Most adult male Chimpanzees that participate in same-sex mounting, genital handling, or other activities also mate with females. Younger (adolescent or juvenile) males, who occasionally engage in such activities as fellatio or mutual genital rubbing, may be less heterosexually involved. In some populations, virtually all adult males participate in same-sex mounting, although such behavior may constitute anywhere from one-fifth to three-quarters of an individual's mounting activity. Females that participate in same-sex activities are also usually functionally bisexual, copulating with males as well. However, a few individuals appear to be more exclusively homosexual: one female, for example, refused to mate with males and was only involved sexually with other females for many years. She even developed a close relationship with another female and her {278} offspring. Socially, she occupied an intermediate position between the male and female subgroups: she often associated with males and "ganged up" with them against other individuals, but she also maintained primary bonds with females and sometimes even defended them against the sexual advances of males. Later, however, she also mated with males.

      Nonreproductive and Alternative Heterosexualities
      Common Chimpanzees engage in a variety of nonprocreative heterosexual practices that parallel their same-sex behaviors. Heterosexual oral sex involves both cunnilingus (males licking the vagina or mouthing the labia) and fellatio (females sucking or nuzzling the penis). Manual stimulation of the genitals also occurs: males sometimes insert a finger into the vagina (the female may then move his hand in order to stimulate herself), while females occasionally fondle their partner's penis. In addition, bumprump takes place between males and females (sometimes including thrusting and scrotum handling), and both sexes masturbate — stimulating their own genitals manually or with various implements. Some males even perform AUTO-FELLATIO, i.e., they suck their own penis. Male Chimpanzees occasionally mount females without achieving penetration or ejaculate after withdrawing; they may also mate with females who are not in heat. Another form of nonprocreative sex is copulation during pregnancy: some females participate in heterosexual activity for 75-80 percent of the time that they are pregnant. In addition, male Chimps have been observed copulating with female Savanna Baboons in the wild.
      When females are in heat, they typically mate numerous times and with multiple partners — as often as six or more times a day (sometimes with two to seven males in quick succession), for a total of several hundred times for each baby conceived. In some cases, though, heterosexual relations are less than amicable: males occasionally try to force females to consort and mate with them by threatening and even violently attacking them, and females often display "blunt refusal" or "abhorrence" reactions toward the advances of older males. Copulations are often interrupted or harassed by other Chimps trying to disrupt the sexual activities. In addition, infanticide and even cannibalism occasionally occur. For example, infants conceived outside the community may be killed by the resident males, and most females mate with males belonging to their own social group. However, in some populations a considerable number of females seek partners outside their group, engaging in "furtive" matings with them. In one community, for example, more than half of all offspring were sired by males living in other groups.
      Although incestuous matings between adults are not common, mothers engage in sexual activity with their infant sons fairly often. Young females typically experience a one-to-three-year period of ADOLESCENT STERILITY after their first menstruation, during which time they mate heterosexually without conceiving. Some adult females practice a unique form of birth control: they simulate the contraceptive effect of nursing by stimulating their own nipples, in some cases preventing pregnancy for up to ten years. Females may also experience a postreproductive or "menopausal" period later in their lives, lasting up to two years (about 4-5 percent {279} of the maximum life span). During this time they often continue to mate, accounting for up to 20 percent of all female sexual activity in a group.

      Sources (* asterisked references discuss homosexuality/transgender)
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      * de Waal, F. B. M., and J. A. R. A. M. van Hooff (1981) "Side-directed Communication and Agonistic Interactions in Chimpanzees." Behavior 77:164-98.
      Wrangham, R. W. (1997) "Subtle, Secret Female Chimpanzees." Science 277:774-75.
      * Yerkes, R. M. (1939) "Social Dominance and Sexual Status in the Chimpanzee." Quarterly Review of Biology 14:115-36.
{280}
Great Apes
      GORILLA (Gorilla gorilla)
IDENTIFICATION: A massive ape (adult males generally weigh over 300 pounds) with black fur; old males are called silverbacks because of the silvery-gray fur on their backs. DISTRIBUTION: Central Africa including Congo (Zaire), Uganda, Rwanda; southeastern Nigeria to southern Congo; endangered. HABITAT: Bamboo forests, rain forests. STUDY AREAS: Virunga Mountains, Rwanda and Congo (Zaire), subspecies G.g. beringei, the Mountain Gorilla; Basel, Metro Toronto, and St. Louis Zoos, subspecies G.g. gorilla, the Lowland Gorilla.

      Social Organization
      Gorillas live in small groups of eight to fifteen individuals, usually consisting of three to six adult females, one mature male, one to two juvenile males, and five to seven immature offspring. All-male groups also regularly occur. The mating system is polygynous, i.e., the mature male mates with all of the females in the group. The females are usually not related to each other, since they generally leave their family group once reaching adulthood — in many other group-living primates, males leave a core group of (usually related) females.

      Description
      Behavioral Expression: Within her group, a female Gorilla sometimes forms an intense pairlike friendship with another female, spending as much time with her as with the breeding male of the group. Her interactions with this "favorite" female consist of constant touching while they spend time together, sitting with each other or lying one against the other, and frequent mutual grooming. Female Gorillas also frequently have sex with other females in their group. In a typical lesbian interaction, one female approaches another directly, often making copulatory vocalizations, after which they may sit quietly together for a while. Often they will begin to fondle each other's genitals or bring their face into intimate contact with the other's vulva, smelling or touching with their mouths. This is usually followed by embracing in a face-to-face position (usually lying down) with rubbing of the genitals against each other, sometimes accompanied by growling, grunting, screaming, or pulsing whimpers. The animals may also pause during periods of pelvic thrusting to caress each other, shift their positions, or masturbate themselves. {281}
      Lesbian sexual activity is notable for its differences from heterosexual copulation, probably related to an emphasis on achieving mutual pleasure. First of all, the more intimate face-to-face position is rarely used between males and females, who instead mate with the male mounting from behind (and often with the male thrusting and vocalizing significantly less than his partner). Sexual interactions between females are also generally more affectionate, involving much more embracing and grooming, and they usually last longer. One study revealed that sexual interactions between females last on average five times longer than heterosexual ones, and that lesbian activity involves considerably more thrusting and genital stimulation.
      Female Gorillas also exhibit clear preferences for particular female sexual partners within their group. Although lesbian activity generally occurs among all members of a group, each female usually has a favorite partner with whom she interacts more often. Homosexuality is also integrated into the general reproductive cycle of the group: breeding females (including mothers) have sex with other females as much as do nonbreeding females, and lesbian sex is common even during pregnancy, sometimes as late as a week or two before birth.
      Although male Gorillas (especially younger animals) sometimes mount each other in cosexual groups, homosexuality occurs most commonly in all-male groups, where probably more than 90 percent of all same-sex activity between males takes place. Such groups result when females leave their home group to join another, or when males occasionally leave their own group upon reaching maturity and band together. All-male groups persist for many years and have a complex network of homosexual pairings. Each male has preferred partners whom he courts and has sex with; some interact with only one other male in the group, while others have multiple partners (up to five have been recorded for one individual). Durations of individual pairings can be anywhere from a few months to a year or more. Participants are sometimes related to each other: in one all-male group, about 40 percent of all homosexual activity occurred between half brothers. There is often intense competition among the males for "preferred" partners — often the younger males — and older, higher-ranking males frequently "guard" their favorite males and fight to protect them from the advances of other males. Nevertheless, rates of aggression are significantly lower in all-male groups than in cosexual groups, and some male groups exhibit a high degree of cohesiveness attributable to the sexual bonding and mediating activities of their members.
      When one male Gorilla is courting another, he approaches while making intense panting sounds; sometimes contact is initiated with one (or both) males reaching out to touch the other, or one may make a more subtle soliciting approach. Sexual activity involves one male mounting another and thrusting, in either the face-to-face or front-to-back position; both males often emit grumbling, growling, or panting sounds. Orgasm is signaled when the animal emits a deep sigh on dismounting, and often there is direct evidence of ejaculation (e.g., semen spilled on his partner). Most males both mount and are mounted, except for the oldest silverback males, who only mount. Like lesbian interactions, male homosexual encounters tend to last, on average, longer than heterosexual ones and to use the {282} face-to-face position more often than in male-female interactions (though less often than between females). Male Gorillas also touch and fondle each other's genitals in addition to mounting one another.

     
Male Gorillas having sex with each other in the mountain rain forests of Rwanda, showing two mounting positions: front-to-back (left) and face-to-face

      Frequency: In cosexual groups, 9 percent of all sexual activity is lesbian and 58 percent of all social/affectionate interactions of females are with other females (mostly with their "favorite" partner); about 2 percent of mounting episodes occur between adult males in such groups. Among younger animals (e.g., adolescents and juveniles) in cosexual groups, 7-36 percent of mounts are between males and 9-14 percent between females. Male homosexual courtship and copulation occur daily in some all-male groups and are thought to exceed the amount of heterosexual activity that takes place in cosexual groups. Some males may engage in homosexual copulation more than 75 times a year in such groups, and homosexual courtship, at its peak, can take place as often as 7 times an hour. Up to 10 percent of groups in some populations are all-male, and Gorillas spend an average of six years in such groups, with some males staying ten or more years (and even occasionally remaining until their death).

      Orientation: Many female Gorillas are bisexual, having sexual and affectionate relationships with both males and females, but there are clear differences in the extent to which various individuals participate in homosexual versus heterosexual activity. In general, it appears that a continuum exists from those females who prefer lesbian activity (they account for a large proportion of the same-sex interactions), to those who have a fairly equal amount of interaction with both males and females, to those who interact primarily with males. Many male Gorillas are probably sequentially {283} bisexual, spending portions of their lives having only homosexual encounters (in all-male groups), followed by periods of only heterosexual interactions, and so on. Other males, especially younger ones, may be simultaneously bisexual. Depending on the circumstances (such as the particular group composition), some males may also have primarily or exclusively homosexual interactions throughout their lives, while others may have only heterosexual ones, but it appears that all males at least have the capacity for bisexuality.

      Nonreproductive and Alternative Heterosexualities
      As noted above, sex (both heterosexual and homosexual) during pregnancy is common among Gorillas. Both males and females also engage in masturbation, and younger animals frequently participate in nonpenetrative sexual activity. Mountings of the latter type are usually incestuous, involving siblings, half siblings, or (more rarely) parents and their offspring (or their siblings' offspring). In captivity, oral sex and manual stimulation of genitals have also been observed in heterosexual interactions. Male Gorillas generally appear to have less interest in sex than females and are sometimes rather reluctant or perfunctory participants in mating. Heterosexual interactions are nearly always initiated by females (whose advances are often initially ignored by the males), males often thrust and vocalize much less than females during copulation (often for no more than 20 seconds), and females generally determine when a particular sexual interaction is finished. However, females may be sexually inactive for up to three or four years while nursing their young. Infanticide is quite common among wild Gorillas: more than 40 percent of all infant deaths in one population were due to infanticide, usually by an adult male trying to gain breeding access to a female (although females have been known to kill infants as well). Probably all adult males commit infanticide at least once during their lifetime, while most females are likely to lose at least one infant during their lifetime to killing by another of their own species.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Coffin, R. (1978) "Sexual Behavior in a Group of Captive Young Gorillas." Boletin de Estudios Medicos y Bi-ologicos 30:65-69.
      * Fischer, R. B. and R.D. Nadler (1978) "Affiliative, Playful, and Homosexual Interactions of Adult Female Lowland Gorillas." Primates 19:657-64.
      * Fossey, D. (1990) "New Observations of Gorillas in the Wild." In Grzimek's Encyclopedia of Mammals, vol. 2, pp. 449-62. New York: McGraw-Hill.
      (1984) "Infanticide in Mountain Gorillas (Gorilla gorilla beringei) with Comparative Notes on Chimpanzees." In G. Hausfater and S. B. Hrdy, eds., Infanticide: Comparative and Evolutionary Perspectives, pp. 217-35. New York: Aldine.
      * --- (1983) Gorillas in the Mist. Boston: Houghton Mifflin.
      * Harcourt, A. H. (1988) "Bachelor Groups of Gorillas in Captivity: The Situation in the Wild." Dodo 25:54-61.
      * --- (1979a) "Social Relations Among Adult Female Mountain Gorillas." Animal Behavior 27:251-64.
      --- — (1979b) "Social Relationships Between Adult Male and Female Mountain Gorillas in the Wild." Animal Behavior 27:325-42.
      * Harcourt, A. H., D. Fossey, K. J. Stewart, and D. P. Watts (1980) "Reproduction in Wild Gorillas and Some Comparisons with Chimpanzees." Journal of Reproduction and Fertility suppl. 28:59-70.
      Harcourt, A. H., and K. J. Stewart (1978) "Sexual Behavior of Wild Mountain Gorillas." In D. J. Chivers and J. Herbert, eds., Recent Advances in Primatology, vol. 1, pp. 611-12. New York: Academic Press. {284}
      * Harcourt, A. H., K. J. Stewart, and D. Fossey (1981) "Gorilla Reproduction in the Wild." In C. E. Graham, ed., Reproductive Biology of the Great Apes, pp. 265-79. New York: Academic Press.
      * Hess, J. P. (1973) "Some Observations on the Sexual Behavior of Captive Lowland Gorillas, Gorilla g. gorilla (Savage and Wyman)." In R. P. Michael and J. H. Crook, eds., Comparative Ecology and Behavior of Primates, pp. 507-81. London: Academic Press.
      * Nadler, R. D. (1986) "Sex-Related Behavior of Immature Wild Mountain Gorillas." Developmental Psychobiology 19:125-37.
      * Porton, I., and M. White (1996) "Managing an All-Male Group of Gorillas: Eight Years of Experience at the St. Louis Zoological Park." In AAZPA Regional Conference Proceedings, pp. 720-28. Wheeling, W.V.: American Association of Zoological Parks and Aquariums.
      * Robbins, M. M. (1996) "Male-Male Interactions in Heterosexual and All-Male Wild Mountain Gorilla Groups." Ethology 102:942-65.
      * --- (1995) "A Demographic Analysis of Male Life History and Social Structure of Mountain Gorillas." Behavior 132:21-47.
      * Schaller, G. (1963) The Mountain Gorilla. Chicago: University of Chicago Press.
      * Stewart, K. J. (1977) "Birth of a Wild Mountain Gorilla (Gorilla gorilla beringei)." Primates 18:965-76.
      Watts, D. P. (1990) "Mountain Gorilla Life Histories, Reproductive Competition, and Sociosexual Behavior and Some Implications for Captive Husbandry." Zoo Biology 9:185-200.
      --- (1989) "Infanticide in Mountain Gorillas: New Cases and a Reconsideration of the Evidence." Ethology 81:1-18.
      * Yamagiwa, J. (1987a) "Intra- and Inter-Group Interactions of an All-Male Group of Virunga Mountain Gorillas (Gorilla gorilla beringei)." Primates 28:1-30.
      * --- (1987b) "Male Life History and the Social Structure of Wild Mountain Gorillas (Gorilla gorilla beringei)." In S. Kawano, J. H. Connell, and T. Hidaka, eds., Evolution and Coadaptation in Biotic Communities, pp. 31-51. Tokyo: University of Tokyo Press.

Great Apes
      ORANG-UTAN (Pongo pygmaeus)
IDENTIFICATION: A medium-sized ape (adult males generally weigh around 170 pounds) with a long, reddish brown coat; some older males develop prominent cheek pads or "flanges." DISTRIBUTION: Sumatra, Borneo (Indonesia); vulnerable. HABITAT: Swamps, lowland and mountain rain forests. STUDY AREAS: Ketambe region of North Sumatra, Indonesia, subspecies P.p. abelii, the Sumatran Orang-utan; Regent's Park Zoo and Singapore Zoological Garden, including subspecies P.p. pygmaeus, the Bornean Orang-utan.
{285}
      Social Organization
      Adult Orang-utans are largely solitary — males and females live separate from each other and interact only when the female is ready to mate. Younger Orangs, however, are more sociable and may actively seek each other's company and interact in groups. The mating system is polygynous: males copulate with multiple females and no long-lasting heterosexual pairing occurs, although males and females may "consort" together for shorter periods during mating. Males do not participate in parenting.

      Description
      Behavioral Expression: Orang-utans engage in a variety of homosexual activities, including a range of different sexual techniques and various affectionate and pairing behaviors. Mounting among male Orangs, especially younger adults (10-15 years old) and adolescents (7-10 years old) often develops into full anal intercourse, with erection of the penis, pelvic thrusting, penetration, and ejaculation. In a more unusual type of homosexual penetration, a male sometimes tries to insert his penis into the small hollow formed when his partner's penis retracts. Another prominent homosexual activity is fellatio (oral-genital contact): one male will lick and suck another's erect penis. In some cases, males take turns fellating each other. Males occasionally also fondle and touch the erect penis of another male, often examining the organ closely by parting the hairs in the genital region. Lesbian activity in Orangs usually involves one female fondling the genitals of another female, often inserting her fingers (thumb or other digits) into the vagina of the other. Sometimes she also masturbates herself with her foot while she is penetrating the other female. Mounting rarely, if ever, occurs among female Orangs, unlike in many other animals in which females engage in homosexual behavior. Female homosexual encounters may last for up to 12 minutes, comparable to the 10-15 minute duration of most heterosexual copulations. Although Orang-utans are usually willing participants in homosexual encounters, sometimes one animal is more reluctant and the partner will then attempt to restrain him or her, for example by using the feet to hold him or her down. However, this contrasts sharply with heterosexual encounters, in which females often scream and struggle violently while males attempt to forcibly mate with them (see the discussion on heterosexualities below).
      Sexual behavior often occurs within a "bonding" or special friendship-like pairing between younger animals of the same sex. Two males or two females may become quite attached, following one another over several days, playing together (including play-wrestling), sharing food, and generally spending a great deal of time together and coordinating their activities. One partner may even throw a "temper tantrum" when the other ventures too far away or fails to wait for its companion. Female Orangs have also been known to compete with males for sexual access to a favorite female partner with whom they later develop a bonded relationship. Same-sex companions demonstrate a number of affectionate behaviors toward each other — females, for example, may embrace, cling to one other, walk in tandem, or groom each other, and males may "kiss" each other. While in {286} some cases this mouth-to-mouth contact may be for the exchange of food or drink, in other cases it appears to be more of an affectionate or greeting gesture. Such companionships also develop between animals of the opposite sex, and indeed they resemble in many ways the "consortships" that sometimes characterize heterosexual mating relations. Companionships, however, need not involve any sexual contact, whether between animals of the same or opposite sex.     
      Homosexual interactions sometimes also occur between male Orangs and Crab-eating Macaques. These monkeys often associate with Orangs, feeding in the same areas and interacting nonaggressively. Orangs and Crab-eating Macaques may groom each other, and male Orang-utans will occasionally suck the penis of an adult male Crab-eating Macaque.
      Transgendered Orang-utans occasionally occur as well: individuals have been found who are physically male yet have a female (XX) chromosome pattern.


Fellatio in two younger male Orang-utans in Sumatra: the male on the lower right is sucking his partner's penis

      Frequency: Approximately 9 percent of all Orang-utan sexual encounters in some populations involve males mounting each other; the proportion of same-sex activity is probably even higher, since male oral-genital contacts and female homosexual encounters are not included in this figure. Females who engage in lesbian activity may do so frequently and repeatedly over several days, similar to the repeated sexual interactions in a heterosexual consortship.

      Orientation: Male homosexual behavior is characteristic of younger Orang-utans. Not all younger males engage in same-sex activity, but those who do are probably bisexual, since most such individuals are also involved in heterosexual pursuits. Mature adult males probably have a bisexual potential: although they rarely engage in homosexual activity in the wild, in captivity they often do (even in the presence of females). Female Orangs are probably also bisexual — for example, one female who was sexually active with another female later mated heterosexually and raised young. However, while engaged in homosexual behavior, she was exclusively lesbian, since she completely ignored males and focused her attentions entirely on other females.

     
A female Orang-utan in the forests of Sumatra masturbating with a tool she made from a piece of liana
{287}
      Nonreproductive and Alternative Heterosexualities
      A wide variety of nonprocreative heterosexual activities are found in Orang-utans. Both males and females often stimulate their partner's genitals with their mouth or hands, and females may also rub their genitals against the male. The female has a prominent clitoris that is stimulated during intercourse, and she often takes the initiative in heterosexual activity, actually mounting the male, manually guiding his penis into her, and performing pelvic thrusts while he lies on his back. A variety of positions are used for heterosexual copulation, including face-to-face (the most common), front-to-back, and sideways. In almost 30 percent of mounts, vaginal penetration and/or ejaculation do not occur. Anal stimulation can be a component of heterosexual interactions as well: both males and females lick, suck, blow on, insert fingers into, and rub their genitals on their partner's anus; males have also been known to engage in anal intercourse (penetration) with females. Females may consort and copulate with multiple male partners, and copulation can occur throughout pregnancy up to the time of birth. Masturbation is also common among Orangs — females rub their fingers or foot on their clitoris or insert a finger or toe into their vagina, while males rub their penises with their fist or foot. Both males and females also use inanimate objects or "tools" to masturbate. Males sometimes become sexually aroused and spontaneously ejaculate during long-calling (a courtship and territorial vocalization used by mature males). Mothers frequently engage in incestuous contact with their infants, manually or orally stimulating the penis or clitoris (or being stimulated by the infant), and may even mount the infants.
      Heterosexual relations are sometimes characterized by aggression and violence rather than pleasure and consensuality. Younger males often chase, harass, and rape females. During such interactions, which may account for the majority of copulations in some populations, the male may grab, slap, bite, and forcibly restrain the female, who struggles violently while screaming or whimpering. Occasionally (about 7-8 percent of the time) she does manage to break free. An unusual form of reproductive suppression also occurs among male Orangs. Although they become sexually mature at seven to ten years old, males generally fail to develop the full range of secondary sexual characteristics (such as the large cheek pads or "flanges," a throat pouch, and a general weight increase) for another seven years, and sometimes this is delayed for as long as two decades. It is thought that this development is suppressed by the presence of a mature male, perhaps through social intimidation or stress, although the exact mechanism is not known. Nonbreeding males have been found to have higher estrogen levels than breeding males, so perhaps a physiological effect is also involved. Interestingly, nonflanged younger males have been observed copulating repeatedly with females without resulting in any pregnancies; perhaps this is related to their arrested sexual development, although it is also possible that they were simply mating during the nonovulatory phase of the female's cycle. In addition, adolescent females experience ADOLESCENT STERILITY, lasting a year or longer, during which they can copulate without becoming pregnant. In fact, adolescent females have higher copulation rates than adult females, accounting for more than 60 percent of heterosexual mating. Adult females breed {288} relatively infrequently, perhaps once every four to eight years. Because females in some populations tend to have synchronized reproductive cycles, there may be periods of up to two years when no adult females are available for mating.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Dutrillaux, B., M.-O. Rethore, and J. Lejeune (1975) "Comparaison du caryotype de l'orang-outang (Pongo pygmaeus) a celui de l'homme, du chimpanze, et du gorille [Comparison of the Karyotype of the Orang-utan to Those of Man, Chimpanzee, and Gorilla]." Annales de Genetique 18:153-61.
      Galdikas, B. M. F. (1995) "Social and Reproductive Behavior of Wild Adolescent Female Orangutans." In R. D. Nadler, B. M. F. Galdikas, L. K. Sheeran, and N. Rosen, eds., The Neglected Ape, pp. 183-90. New York: Plenum Press.
      --- (1985) "Orangutan Sociality at Tanjung Puting." American Journal of Primatology 9:101-19.
      --- (1981) "Orangutan Reproduction in the Wild." In C. E. Graham, ed., Reproductive Biology of the Great Apes, pp. 281-300. New York: Academic Press.
      Harrisson, B. (1961) "A Study of Orang-utan Behavior in the Semi-Wild State." International Zoo Yearbook 3:57-68.
      Kaplan, G., and L. Rogers (1994) Orang-Utans in Borneo. Armidale, Australia: University of New England Press.
      Kingsley, S. R. (1988) "Physiological Development of Male Orang-utans and Gorillas." In J.H. Schwartz, ed., Orang-utan Biology, pp. 123-31. New York: Oxford University Press.
      --- (1982) "Causes of Nonbreeding and the Development of the Secondary Sexual Characteristics in the Male Orang Utan: A Hormonal Study." In L. E. M. de Boer, ed., The Orang Utan: Its Biology and Conservation, pp. 215-29. The Hague: Dr W. Junk Publishers.
      * MacKinnon, J. (1974) "The Behavior and Ecology of Wild Orang-utans (Pongo pygmaeus)." Animal Behavior 22:3-74.
      * Maple, T. L. (1980) Orang-utan Behavior. New York: Van Nostrand Reinhold.
      Mitani, J. C. (1985) "Mating Behavior of Male Orangutans in the Kutai Game Reserve, Indonesia." Animal Behavior 33:392-402.
      * Morris, D. (1964) "The Response of Animals to a Restricted Environment." Symposia of the Zoological Society of London 13:99-118.
      Nadler, R. D. (1988) "Sexual and Reproductive Behavior." In J. H. Schwartz, ed., Orang-utan Biology, pp. 105-16. New York: Oxford University Press.
      --- (1982) "Reproductive Behavior and Endocrinology of Orang Utans." In L. E. M. de Boer, ed., The Orang Utan: Its Biology and Conservation, pp. 231-48. The Hague: Dr W. Junk Publishers.
      * Poole, T. B. (1987) "Social Behavior of a Group of Orangutans (Pongo pygmaeus) on an Artificial Island in Singapore Zoological Gardens." Zoo Biology 6:315-30.
      * Rijksen, H. D. (1978) A Fieldstudy on Sumatran Orang Utans (Pongo pygmaeus abelii Lesson 1827): Ecology, Behavior, and Conservation. Wageningen, Netherlands: H. Veenman & Zonen b.v.
      Rodman, P. S. (1988) "Diversity and Consistency in Ecology and Behavior." In J. H. Schwartz, ed., Orang-utan Biology, pp. 31-51. New York: Oxford University Press.
      Schurmann, C. (1982) "Mating Behavior of Wild Orang Utans." In L. E. M. de Boer, ed., The Orang Utan: Its Biology and Conservation, pp. 269-84. The Hague: Dr W. Junk Publishers.
      Schurmann, C., and J. A. R. A. M. van Hooff (1986) "Reproductive Strategies of the Orang-Utan: New Data and a Reconsideration of Existing Sociosexual Models." International Journal of Primatology 7:265-87.
      * Turleau, C., J. de Grouchy, F. Chavin-Colin, J. Mortelmans, and W. Van den Bergh (1975) "Inversion peri-centrique du 3, homozygote et heterozygote, et translation centromerique du 12 dans une famille d'orangs-outangs. Implications evolutives [Pericentric Inversion of Chromosome 3, Homozygous and Heterozygous, and Transposition of Centromere of Chromosome 12 in a Family of Orang-utans. Implications for Evolution]." Annales de Genetique 18:227-33.
      Utani, S., and T. M. Setia (1995) "Behavioral Changes in Wild Male and Female Sumatran Orangutans (Pongo pygmaeus abelii) During and Following a Resident Male Take-over." In R. D. Nadler, B.M.F. Galdikas, L.K. Sheeran, and N. Rosen, eds., The Neglected Ape, pp. 183-90. New York: Plenum Press.
{289}
Gibbons or Lesser Apes
      WHITE-HANDED GIBBON (Hybolates lar)
IDENTIFICATION: A small ape (weighing up to 13 pounds) with a variable coat color (cream, black, brown, or reddish) and a white face ring, hands, and feet. DISTRIBUTION: China, Thailand, Laos, Burma, Malay Peninsula, Sumatra. HABITAT: Lowland and mountain deciduous and rain forests. STUDY AREAS: Huai Kha Khaeng Wildlife Sanctuary, Thailand.
      SIAMANG (Hybolates syndactylus)
IDENTIFICATION: Similar to White-handed Gibbon, but larger (up to 24 pounds), with all-black fur and a prominent throat sac. DISTRIBUTION: Sumatra, Malay Peninsula. HABITAT: Lowland and mountain forests. STUDY AREA: Milwaukee County Zoo, Wisconsin.

      Social Organization
      Gibbons generally live in family groups consisting of a paired male and female and their offspring. Siamang heterosexual pairs may be more closely bonded than those of White-handed Gibbons. Both males and females perform complex vocal duets as part of bonding and territorial displays, although separate family groups have relatively little interaction with one another.

      Description
      Behavioral Expression: Within their nuclear family groups, male Gibbons sometimes engage in homosexual activities with each other. This incestuous activity often takes place between an adolescent or younger male and his father (or stepfather, if his parents have divorced and re-paired); in Siamangs it may also occur between brothers. A typical homosexual encounter between father and son in White-handed Gibbons occurs in the trees in the morning or early afternoon, while the family is resting or feeding. The mother is generally nonchalant about such encounters, ignoring the sexual activity even if she is close at hand. The two males often groom each other or engage in playful wrestling or chasing as part of their interaction. During such activities, either male may approach the other to initiate sex, which consists primarily of the two males rubbing their erect penises together, {290} often leading to orgasm. This is done face-to-face (unlike heterosexual copulation, which is typically performed front-to-back). The father lifts up his knees and spreads his legs wide while sitting on a branch or hanging by his arms — this is an invitation to his son to have sex. The adolescent male embraces his father around the waist with his legs, then lowers his body until he is, in effect, sitting in his father's lap, with his legs resting on top of the older male's thighs. This allows their genitals to come into direct contact, and the younger male usually begins rapidly thrusting against his father; sometimes the older male will make pelvic thrusts as well. If his son ejaculates on him, the father may scoop up the semen and eat it. Genital contact can last for up to a minute, although the average is about 20 seconds; in comparison, heterosexual copulations in this species average only about 15 seconds.
      A similar form of genital rubbing occurs between father and son in Siamangs. While both males are hanging by their arms, the younger grasps his father around the waist with his legs and both thrust against each other (in this species, heterosexual mating is occasionally also performed face-to-face). Unlike in White-handed Gibbons, this activity is sometimes accompanied by threats between the two males, and it appears that the younger male may on occasion want to terminate the activity before his father does. Sometimes two brothers — juveniles or adolescents, four to nine years old — thrust against each other face-to-face as well. Brothers are also generally affectionate with each other, touching and grooming one another, putting their arms over each other's shoulders, and wrestling together. Fellatio also sometimes occurs in Siamangs: usually an older brother will lick and gently nibble on the penis and groin of his younger brother (who may be only one to three years old) while the latter dangles by his arms above him or sits with his legs spread. The older male may also masturbate the younger by pulling on his erect penis; if ejaculation occurs, the semen may be eaten. Occasionally, a son will lick and groom his father's genital area, or the father might insert one of his fingers into his son's anus.

      Frequency: In those Gibbon families where homosexual activity takes place, it occurs quite frequently, and at rates that may equal or exceed heterosexual activity. In one White-handed Gibbon family, the father and son sometimes had sexual encounters as often as 8 times a day — although they averaged about twice a day — and homosexual activity took place on more than a third of the days that the family was observed. In fact, during one 18-day period, 44 homosexual interactions were recorded. In comparison, 23 heterosexual copulations were observed in another family over 18 (different) days, at a rate of 1-3 per day; other studies have found rates of 2 heterosexual matings per day (equivalent to heterosexual activity on about a third of the observation days). In a Siamang family observed in a zoo, about 30 percent of all sexual interactions were between males. It is not yet known, however, in what proportion of families homosexual activity occurs (in either of these species).

      Orientation: Male Gibbon sexual life is probably sequentially bisexual, characterized by alternating periods of heterosexual and homosexual activity, with {291} occasional long-term exclusive homosexuality. Younger males may experience entirely homosexual interactions with their fathers, or sexual activity with both parents (see below) while they are growing up, and then go on to mate heterosexually as adults. Once paired with a female, they may engage in incestuous encounters with their offspring of both sexes or have extended periods of exclusive homosexuality. In one White-handed Gibbon family, no heterosexual interactions were observed between the father and his female mate during the entire two years that homosexual activity was taking place between him and his son.

      Nonreproductive and Alternative Heterosexualities
      Like many other species where homosexual activity occurs between related individuals, heterosexual incest is also prominent among Gibbons. Siamang mothers and fathers both interact sexually with their offspring of the opposite sex, as do siblings. Adult males sometimes perform copulation-like thrusting with their daughters, as well as oral and manual stimulation of their genitals. In one case, a Siamang father was observed fondling his adolescent daughter's vulva with his fingers while her younger brother licked her clitoris. Mothers may invite their juvenile sons — as young as four to five years — to lick and groom their genitals (usually with no hostile reaction from the father). When offspring grow up, mother-son pairs (and occasionally, brother-sister pairs) may sometimes develop in both White-handed Gibbons and Siamangs, often when a father dies and is replaced by his son. Nonreproductive sexual behaviors such as oral sex are also commonly performed in non-incestuous contexts, e.g., between a pair-bonded male and female. Cunnilingus (including direct clitoral licking), manual fondling of the vulva, and vaginal penetration with the fingers have all been observed in mated pairs. Females probably also experience orgasm during heterosexual encounters: in one episode in which a male and female were thrusting against each other, a shudder coursed through the female's body, and she remained still for almost half a minute after a period of intense stimulation. Female White-handed Gibbons sometimes masturbate by rubbing their genitals against a surface, and they may experience orgasm this way; male Siamangs also masturbate, though not necessarily to orgasm.
      In White-handed Gibbons, about 6-7 percent of heterosexual copulations occur when the female cannot conceive, e.g., during pregnancy or lactation. Some of these matings may be with males other than her mate. Although most Gibbon pairs are monogamous, it is estimated that 10-12 percent of White-handed Gibbon copulations are promiscuous. Nonmonogamous sexual activity also occurs in Siamangs and may be initiated by the female. Similarly, although many Gibbons (of both species) pair for life, divorce also occurs. In one study that followed 11 Gibbon heterosexual pairs over six years, 5 of them split up — usually when one partner left his or her mate to be with another individual. As a result, many White-handed Gibbon families — perhaps up to a third — involve step-parenting. Interestingly, even though there is a wide variety of possible sexual and pairing activities in these species, heterosexual activity is a relatively rare occurrence in wild Gibbons. For example, sexual behavior between male and female White-handed Gibbons generally occurs only once every two years or so, and for periods of only four or five months {292} at a time when it does (females generally breed only every two to three years). In Siamangs, females go through regular periods of asexuality in which they delay breeding and turn over the care of their young to males. Females of this species look after their young only until they are 12-16 months old; at that time, males assume full responsibility for the offspring, but females do not reproduce again for another year. It is thought that this period of nonreproduction enables them to assume leadership roles in their group.

      Sources (* asterisked references discuss homosexuality/transgender)
      Brockelman, W. Y., U. Reichard, U. Treesucon, and J. J. Raemaekers (1998) "Dispersal, Pair Formation, and Social Structure in Gibbons (Hylobates lar)." Behavioral Ecology and Sociobiology 42:329-39.
      Chivers, D. J. (1974) The Siamang in Malaya: A Field Study of a Primate in Tropical Rain Forest. Contributions to Primatology, vol. 4. Basel: S. Karger.
      --- . (1972) "The Siamang and the Gibbon in the Malay Peninsula." In D. M. Rumbaugh, ed., Gibbon and Siamang, vol.1, pp. 103-35. Basel: S. Karger.
      Chivers, D. J., and J. J. Raemaekers (1980) "Long-term Changes in Behavior." In D. J. Chivers, ed., Malayan Forest Primates: Ten Years' Study in Tropical Rain Forest, pp. 209-60. New York: Plenum.
      * Edwards, A.-M. A. R., and J. D. Todd (1991) "Homosexual Behavior in Wild White-handed Gibbons (Hylobates lar)." Primates 32:231-36.
      Ellefson, J. O. (1974) "A Natural History of White-handed Gibbons in the Malayan Peninsula." In D. M. Rumbaugh, ed., Gibbon and Siamang, vol. 3, pp. 1-136. Basel: S. Karger.
      * Fox, G. J. (1977) "Social Dynamics in Siamang." Ph.D. thesis, University of Wisconsin-Milwaukee.
      --- (1972) "Some Comparisons Between Siamang and Gibbon Behavior." Folia Primatologica 18:122- 39.
      Koyama, N. (1971) "Observations on Mating Behavior of Wild Siamang Gibbons at Fraser's Hill, Malaysia." Primates 12:183-89.
      Leighton, D. R. (1987) "Gibbons: Territoriality and Monogamy." In B. B. Smuts, D. L. Cheney, R. M. Seyfarth, R. W. Wrangham, and T. T. Struhsaker, eds., Primate Societies, pp. 135-45. Chicago: University of Chicago Press.
      Mootnick, A. R., and E. Baker (1994) "Masturbation in Captive Hylobates (Gibbons)." Zoo Biology 13:345- 53.
      Palombit, R. (1996) "Pair Bonds in Monogamous Apes: A Comparison of the Siamang Hylobates syndacty-lus and the White-handed Gibbon Hylobates lar." Behavior 133:321-56.
      --- (1994a) "Dynamic Pair Bonds in Hylobatids: Implications Regarding Monogamous Social Systems." Behavior 128:65-101.
      --- (1994b) "Extra-pair Copulations in a Monogamous Ape." Animal Behavior 47:721-23.
      Raemaekers, J. J., and P. M. Raemaekers (1984) "Vocal Interaction Between Two Male Gibbons, Hylobates lar." Natural History Bulletin of the Siam Society 32:95-106.
      Reichard, U. (1995a) "Extra-pair Copulation in Monogamous Wild White-handed Gibbons (Hylobates lar)." Zeitschrift fur Saugetierkunde 60:186-88.
      --- (1995b) "Extra-pair Copulation in a Monogamous Gibbon (Hylobates lar)." Ethology 100:99-112.
{293}
      LANGURS AND LEAF MONKEYS
Langurs
      HANUMAN LANGUR (Presbytis entellus)
IDENTIFICATION: A medium-sized monkey with a silver-gray or brown coat, black face, slender limbs, and a long tail (over 3 feet). DISTRIBUTION: Throughout India, Pakistan, Bangladesh, Sri Lanka, Burma. HABITAT: Scrub and deciduous forests. STUDY AREAS: Numerous locations in India, including Jodhpur, Abu, Kumaon Hills; Polonnaruwa, Sri Lanka; Melemchi, Nepal; University of California-Berkeley.
      NILGIRI LANGUR (Presbytis johnii)
IDENTIFICATION: Similar to Hanuman Langur but with shiny black fur, a light brown hood, and a prominent brow tuft. DISTRIBUTION: Southwestern India; vulnerable. HABITAT: Montane evergreen rain forests, woodlands. STUDY AREAS: Nilgiri district, Mundanthurai Tiger Reserve, Anaimalai Wildlife Sanctuary, India.

      Social Organization
      Hanuman Langurs live in cosexual troops (some contain only one male) and also in all-male groups. The latter typically include up to 30 or more individuals; about 20 percent of the population in some areas lives in male-only groups. Nilgiri Langurs live in both cosexual troops (usually eight to nine monkeys each, with one or two adult males) and same-sex groupings (usually two or three males, occasionally more, constituting about a quarter to a third of the adult males). Troop life and stability generally revolve around the females; males are distinctly peripheral to the overall social system, playing only a minor role in defending the troop and minimally helping raise the young.


A female Hanuman Langur in India mounting another female
{294}
      Description
      Behavioral Expression: Homosexual mounting is a prominent feature of female interactions in Hanuman Langurs. One female climbs on the back of another and begins pelvic thrusting. Unlike in other species that engage in homosexual mounting, the female does not rub her genitals on the rump of the other female, but rather thrusts against her buttocks. The mounter may experience indirect stimulation of the area surrounding her clitoris, while the mountee may have direct clitoral stimulation from the female on top of her. In many ways such mounts resemble heterosexual matings, for example in their duration (5 to 10 seconds), number of pelvic thrusts (two to eleven), the grunting and grimacing of the mounter, and the JUMPING DISPLAY, which often precedes or follows. In other respects, however, homosexual mountings are strikingly different. For example, most heterosexual matings are solicited by the female, who lowers her head and shakes it while presenting her hindquarters to the male. While a similar solicitation occurs in about 13 percent of mounts between females, the majority (79 percent) are initiated by the mounting female. In both homosexual and heterosexual mounts, the partners groom following a mount; however, between females the mounter usually grooms the mountee, while in heterosexual mounts, the mountee (female) typically grooms the mounter (male). Finally, only about 30 percent of homosexual mounts are interrupted by other individuals; in contrast, more than 80 percent of heterosexual copulations are harassed by other animals trying to disrupt (and prevent) the mating. Up to seven animals of all ages and sexes may converge on an opposite-sex mating pair and directly attack the animals, slapping them, trying to push the male off or chase the female out from under him, and even kicking the male's testicles.
      All females participate freely in homosexual mounting, including lactating, pregnant, menstruating, ovulating, and nonovulating females. This behavior is especially common among mothers, who have developed a special "baby-sitting" system: they transfer their young to other individuals in the troop (usually other females but sometimes males) for a short time (a similar pattern is found in Nilgiri Langurs). This allows them to engage in homosexual (and other) activities. Most mounting between females occurs among adults, though some involves adults with {295} juveniles (up to four years old), usually with the younger female mounting the older one. Although most homosexual participants are unrelated, some mountings are incestuous, mostly between half sisters (about 27 percent of all lesbian mounts) and, more rarely, between mother and daughter (about 1 percent of mounts); heterosexual matings are virtually never incestuous.
      Male Hanuman Langurs mount each other as well, especially in the all-male bands. Unlike homosexual mounting between females, this activity is typically initiated by the mountee, who invites another male to mount him by performing a head-shaking display (sometimes combined with small jumps and "snoring" vocalizations). Mounting often involves one male rubbing and thrusting his erect penis against the other's body and may be accompanied by a number of affectionate activities that are typically associated with sexual arousal. These include embracing (in which one male buries his head in the chest or shoulder of another), mouth-to-mouth contact or "kissing," reciprocal grooming (often accompanied by erections), and touching or grooming of the genitals with the hand or lips. Males also "cuddle," one sitting closely behind the other, resting his head on the back of the male seated between his legs while touching his loins. Hanuman males sometimes form DOUS — companionships in which two males live and travel together, visiting troops in other areas or sometimes settling into all-male bands. Some duos are short-lived (a month or less), others more long-lasting.
      Male Nilgiri Langurs also interact erotically with each other in a number of ways, usually incorporating three types of activities: grooming, embracing, and mounting. These are not entirely separate behaviors, and they often combine with each other. Grooming is an intensely pleasurable, relaxing, and arousing experience: one or both males usually get an erection during grooming, and this may lead to ejaculation (a male may even eat his own semen afterward). In embracing, one monkey runs up to another and gives him a long, clinging hug; this is often combined with grooming and has a noticeable soothing effect. Male Nilgiri Langurs also mount each other, using the same position as for heterosexual intercourse. One male may directly approach another male and present his hindquarters to the other, or else he may go through a more stylized presentation known as REAR-END FLIRTATION, in which he slowly walks by the other male and turns his hindquarters toward him as he passes by. During same-sex mounting, one male climbs on top of the other's rump, grabbing the mounted monkey by the ankles with his feet while making pelvic thrusts (often simultaneously mouthing his back); the mountee sometimes looks or reaches back to grasp the other male. Following mounting, the monkeys often groom or embrace-groom. In cosexual troops with more than one male, two males who engage in homosexual mounting may cooperate in launching attacks against males in neighboring groups.
      Intersexual Hanuman Langurs also occur: for example, anatomically male animals with female chromosomes (XX) have been documented. This is thought to be the result of a "sex change" in the chromosomal structure of the animal.

      Frequency: Female homosexual mounting is a common and regular occurrence in Hanuman Langurs, comprising 37 percent of all mounting activity in {296} some regions; each female participates in a homosexual mount roughly once every five days, usually in the morning or late afternoon. There is also considerable geographic variation in the frequency of mounting between females. Male homosexual mounting in both Hanuman and Nilgiri Langurs is less common, though it can occur frequently in Hanuman all-male bands (especially during periods of excitement). In one study, more than 40 homosexual interactions between male Hanumans were observed during three months. Among Nilgiri Langur males, nearly half of all grooming sessions are between males and over 10 percent of embracing is between males.

      Orientation: All female Hanuman Langurs participate in homosexual activity, to varying degrees; most females are probably bisexual, also mating heterosexually to a greater or lesser extent. Male Hanuman Langurs are probably sequentially bisexual, since each male spends some part of his life in an all-male band, where homosexual activities typically occur — and at any given time, as much as 75-90 percent of the male population may be living in such bands. Some males are exclusively homosexual for long periods, since they may stay in these bands for more than five years — in some cases, decade-long residencies have been documented. In fact, some males never mate heterosexually, since they spend their entire adult lives in all-male bands. The highest-ranking male in a Nilgiri Langur troop engages in both homosexual and heterosexual mounting. The other males in the group, however, participate only in homosexual mounting during their stay in the troop, which can last for four or more years.

      Nonreproductive and Alternative Heterosexualities
      A large proportion of male Hanuman Langurs are nonbreeding: about a quarter of all males never reproduce during their lifetime, and (as noted above) the majority of the male population lives in all-male bands. Individual females occasionally go through nonbreeding periods in which menstruation may cease for months at a time. Furthermore, both males and females experience a postreproductive or "menopausal" period later in their lives: about 14 percent of the female population consists of nonbreeding older females who nevertheless are still sexually active. This period can last up to nine years, fully one-quarter of the average female's life span. Males frequently rejoin all-male bands after they have bred, where they live out the remainder of their lives (six or more years). Langurs also participate in a variety of nonprocreative sexual behaviors during their breeding prime: in Hanumans, about 8 percent of copulations occur outside of the female's fertilizable period, while sexual activity during pregnancy is common (especially during the second and third months of the six-to-seven-month gestation period). Females also occasionally mount males, while adult-juvenile heterosexual interactions also occur. Male Nilgiri Langurs often masturbate, and in some populations of this species, heterosexual mating is remarkably infrequent. In fact, the sexes often lead largely separate lives: adult males and females hardly ever interact with one another, and most social interactions take place within small subgroups consisting of monkeys of the same sex and age. {297}
      The breeding system of Hanuman Langurs is in many ways characterized by hostility and violence between the sexes and toward infants. As mentioned above, group members often harass and disrupt heterosexual matings, with the result that less than half of all copulations are completed (harassment also occurs in more than three-quarters of Nilgiri Langur copulations). Moreover, a systematic pattern of infanticide is prominent in Hanuman Langurs: males attempting to gain sexual access to females often brutally kill their infants. In some populations, infanticide accounts for as many as 30-60 percent of all infant deaths. The stress of male takeover attempts also sometimes results in abortion of fetuses, and in a few cases females even appear to induce the abortions themselves rather than have their babies subsequently killed by a male. For example, pregnant females may press and slide their bellies on the ground or allow other females to climb on or jump forcefully against them. During the raising of infants, abuse and neglect by females is also not uncommon, occurring in 12 percent of mother-infant interactions and 17 percent of "baby-sitter" interactions. Mistreatment includes abandonment; dangling, dropping, or dragging of the baby; shoving it against the ground; biting; and even kicking and throwing infants out of trees. Remarkably, infants are rarely seriously hurt as a result of such behaviors, although a few deaths (including choking) have been documented. In addition, young females from one group sometimes "kidnap" a baby from a neighboring group, keeping the infant for up to 33 hours before its mother is able to retrieve it. Occasionally the stolen baby dies as a result of the mishandling or neglect it experiences during a kidnapping.

      Sources (* asterisked references discuss homosexuality/transgender)
      Agoramoorthy, G., and S. M. Mohnot (1988) "Infanticide and Juvenilicide in Hanuman Langurs (Presbytis entellus) Around Jodhpur, India." Human Evolution 3:279-96.
      Agoramoorthy, G., S. M. Mohnot, V. Sommer, and A. Srivastava (1988) "Abortions in Free-ranging Hanuman Langurs (Presbytis entellus) — a Male Induced Strategy?" Human Evolution 3:297-308.
      Borries, C. (1997) "Infanticide in Seasonally Breeding Multimale Groups of Hanuman Langurs (Presbytis entellus) in Ramnagar (South Nepal)." Behavioral Ecology and Sociobiology 41:139-50.
      * Dolhinow, P. (1978) "A Behavioral Repertoire for the Indian Langur (Presbytis entellus)." Primates 19:449- 72.
      * Egozcue, J. (1972) "XX Male Presbytis entellus? A Retrospective Study." Folia Primatologica 17:292-96.
      * Hohmann, G. (1989) "Group Fission in Nilgiri Langurs (Presbytis johnii)." International Journal of Primatology 10:441-54.
      Hohmann, G., and L. Vogl (1991) "Loud Calls of Male Nilgiri Langurs (Presbytis johnii): Age-, Individual-, and Population-Specific Differences." International Journal of Primatology 12:503-24.
      Hrdy, S. B. (1978) "Allomaternal Care and Abuse of Infants Among Hanuman Langurs." In D. J. Chivers and J. Herbert, eds., Recent Advances in Primatology, vol. 1, pp. 169-72. London: Academic Press.
      * --- (1977) The Langurs of Abu: Male and Female Strategies of Reproduction. Cambridge, Mass.: Harvard University Press.
      Johnson, J. M. (1984) "The Function of All-Male Trouping Structure in the Nilgiri Langur, Presbytis johnii." In M. L. Roonwal, S. M. Mohnot, and N. S. Rathore, eds., Current Primate Researches, p. 397. Jodhpur, India: Jodhpur University.
      * Mohnot, S. M. (1984) "Some Observations on All-Male Bands of the Hanuman Langur, Presbytis entellus." In M. L. Roonwal, S. M. Mohnot, and N. S. Rathore, eds., Current Primate Researches, pp. 343-59. Jodhpur, India: Jodhpur University.
      --- (1980) "Intergroup Infant Kidnapping in Hanuman Langur." Folia Primatologica 34:259-77.
      * Poirier, F. E. (1970a) "The Nilgiri Langur (Presbytis johnii) of South India." In L. A. Rosenblum, ed., Primate Behavior: Developments in Field and Laboratory Research, vol .1, pp. 251-383. New York: Academic Press. {298}
      * --- (1970b) "The Communication Matrix of the Nilgiri Langur (Presbytis johnii) of South India." Folia Primatologica 13:92-136.
      --- (1969) "Behavioral Flexibility and Intertroop Variation Among Nilgiri Langurs (Presbytis johnii) of South India." Folia Primatologica 11:119-33.
      Rajpurohit, L. S., V. Sommer, and S. M. Mohnot (1995) "Wanderers Between Harems and Bachelor Bands: Male Hanuman Langurs (Presbytis entellus) at Jodhpur in Rajasthan." Behavior 132:255-99.
      Sommer, V. (1989a) "Sexual Harassment in Langur Monkeys (Presbytis entellus): Competition for Nurture, Eggs, and Sperm?" Ethology 80:205-17.
      --- (1989b) "Infant Mistreatment in Langur Monkeys — Sociobiology Tackled from the Wrong End?" In A. E. Rasa, C. Vogel, and E. Voland, eds., The Sociobiology of Sexual and Reproductive Strategies, pp. 110-27. London and New York: Chapman and Hall.
      * --- (1988) "Female-Female Mounting in Langurs (Presbytis entellus)." International Journal of Primatology 8:478.
      Sommer, V., and L. S. Rajpurohit (1989) "Male Reproductive Success in Harem Troops of Hanuman Langurs (Presbytis entellus)." International Journal of Primatology 10:293-317.
      Sommer, V., A. Srivastava, and C. Borries (1992) "Cycles, Sexuality, and Conception in Free-Ranging Langurs (Presbytis entellus.)" American Journal of Primatology 28:1-27.
      * Srivastava, A., C. Borries, and V. Sommer (1991) "Homosexual Mounting in Free-Ranging Female Hanuman Langurs (Presbytis entellus.)" Archives of Sexual Behavior 20:487-516.
      Tanaka, J. (1965) "Social Structure of Nilgiri Langurs." Primates 6:107-22.
      Vogel, C. (1984) "Patterns of Infant-Transfer within Two Troops of Common Langurs (Presbytis entellus) Near Jodhpur: Testing Hypotheses Concerning the Benefits and Risks." In M. L. Roonwal, S. M. Mohnot, and N. S. Rathore, eds., Current Primate Researches, pp. 361-79. Jodhpur, India: Jodhpur University.
      * Weber, I. (1973) "Tactile Communication Among Free-ranging Langurs." American Journal of Physical Anthropology 38:481-86.
      * Weber, I., and C. Vogel (1970) "Sozialverhalten in ein- und zweigeschlechtigen Langurengruppen [Social Behavior in Unisexual and Heterosexual Langur Groups]." Homo 21:73-80.
      * Weinrich, J. D. (1980) "Homosexual Behavior in Animals: A New Review of Observations From the Wild, and Their Relationship to Human Sexuality." In R. Forleo and W. Pasini, eds., Medical Sexology: The Third International Congress, pp. 288-95. Littleton, Mass.: PSG Publishing.
{299}
Leaf Monkeys
      PROBOSCIS MONKEY (Nasalis larvatus)
IDENTIFICATION: A long-tailed monkey with a reddish orange to gray coat; males are bigger than females (weighing up to 50 pounds) and develop an enlarged, pendulous nose with age. DISTRIBUTION: Borneo; vulnerable. HABITAT: Coastal swamp forests. STUDY AREAS: Tanjung Puting National Park in Kalimantan Tengah, Indonesia.
      GOLDEN MONKEY (Pygathrix roxellana)
IDENTIFICATION: A medium-sized, long-tailed monkey with a dark brown back and tail; golden orange chest, underparts, and elongated shoulder hairs; and a prominent white muzzle and blue face. DISTRIBUTION: South-central China; vulnerable. HABITAT: Mountain coniferous and bamboo forests. STUDY AREAS: Beijing Raising and Training Center for Endangered Animals, China; subspecies R.r. roxellana.

      Social Organization
      Both Proboscis and Golden Monkeys usually live in polygamous groups consisting of one male and several adult females (five on the average), along with several adolescent or juvenile females. Younger male Proboscis Monkeys sometimes join all-male troops before reaching adolescence — such groups contain males of all ages, including adults — while some male Golden Monkeys are solitary or peripheral. Cosexual groups of Proboscis Monkeys are female-centered, since female Proboscis Monkeys direct most of their behaviors — both friendly and aggressive — toward other females rather than males, and such female relationships hold the group together. In many cases females also take the initiative in directing the movement of the group, for example when leaving a sleeping tree or crossing a river. Although little else is known about the social organization of Golden Monkeys, it appears that they may also gather into huge troops — up to 600 animals — which are among the largest groupings found in any tree-living primate.

      Description
      Behavioral Expression: Both male and female Proboscis Monkeys participate in homosexual mounting. An adult female may mount another from behind, in a position similar to heterosexual mounting, and thrust against her. Such behavior {300} sometimes occurs when two social groups meet each other. Unlike heterosexual copulation, lesbian mounting is usually not preceded by solicitation behavior on the part of the female being mounted (solicitation involves a special "pout" face with pursed lips, shaking of the head from side to side, and presentation of the hindquarters to the mounting animal). Male homosexual mounting — also in the front-to-back position, and with pelvic thrusting — occurs in younger animals (adolescents or juveniles) and is often a part of play-wrestling matches. It may also be interspersed with masturbation, in which the mounting male stimulates his penis with his hand. In some cases, the male being mounted may not be an entirely willing participant and will try to get away as the other male restrains him by biting gently on the neck; similar escape behavior is sometimes shown by females during heterosexual mounting. In Golden Monkeys, homosexual behavior has only been seen among females and again consists of one female mounting another.

      Frequency: Same-sex mounting probably occurs only occasionally in Proboscis and Golden Monkeys. However, in Proboscis Monkeys at least, heterosexual mounting is also infrequent: in one study, only 12 mountings were observed over an entire year, and 2 of these (17 percent) were same-sex.

      Orientation: Female Proboscis Monkeys that engage in same-sex mounting are probably bisexual, since they may alternate same-sex and opposite-sex activity during the same session. Golden Monkey females probably have a bisexual potential, since same-sex mounting has so far only been observed in captive situations when males are not present, and all such females engaging in same-sex mounting also mated heterosexually and raised young.

      Nonreproductive and Alternative Heterosexualities
      As noted above, female Proboscis Monkeys often refuse heterosexual copulation by breaking away from the male during mounting. A male may exhibit indifference to a female's solicitations as well, either ignoring her completely or snarling at her to indicate his unwillingness. Male Golden Monkeys also frequently ignore females' sexual invitations: nearly 50 percent of all female invitations fail to result in mounting by the male. Furthermore, many mounts by males do not result in ejaculation: for some Golden males, 18-97 percent of their copulations are nonejaculatory. Females, however, display an intense interest in sexual activity, frequently soliciting the male and copulating repeatedly — one female solicited a male 34 times, and was mounted 23 times, in one day. REVERSE mountings, in which the female mounts the male, are common in Golden Monkeys as well, accounting for anywhere from 3-40 percent of all heterosexual mounts. In such cases, the male usually adopts the prostrate solicitation posture typical of females inviting copulation. Heterosexual copulations in Proboscis Monkeys are sometimes also harassed or interrupted by younger animals, who try to disrupt the mating pair by climbing on the male, pulling at his nose, or making noises and distracting movements. Female Proboscis Monkeys often have sex when they are pregnant, in some cases {301} soliciting copulations from males as late as two weeks before birth. In fact, heterosexual mating may occur more frequently during pregnancy than at any other time of the year. Golden Monkeys engage in sexual mounting outside of the mating season, and females often solicit sexual behavior while they are menstruating. As noted above, masturbation in Proboscis Monkeys may occur in same-sex contexts; similar behavior has been observed in heterosexual contexts among Golden Monkeys. In such cases, both males and females may eat the semen after ejaculation. A number of adult, sexually mature Proboscis males are nonbreeders, since they live in all-male groups: in one population, such individuals comprised 28 percent of all adult males. Solitary male Golden Monkeys are probably also nonbreeders.

      Sources (* asterisked references discuss homosexuality/transgender)
      Clarke, A. S. (1991) "Sociosexual Behavior of Captive Sichuan Golden Monkeys (Rhinopithecus roxellana)." Zoo Biology 10:369-74.
      Gorzitze, A. B. (1996) "Birth-related Behaviors in Wild Proboscis Monkeys (Nasalis larvatus)." Primates 37:75-78.
      Kawabe, M., and T. Mano (1972) "Ecology and Behavior of the Wild Proboscis Monkey, Nasalis larvatus (Wurmb) in Sabah, Malaysia." Primates 13:213-27.
      Poirier, F. E., and H. Hongxhin (1983) "Macaca mulatta and Rhinopithecus in China: Preliminary Research Results." Current Anthropology 24:387-88.
      Qi, J.-F. (1988) "Observation Studies on Reproduction of Golden Monkeys in Captivity: I. Copulatory Behavior." Acta Theriologica Sinica 8:172-75.
      * Ren, R., K. Yan, Y. Su, H. Qi, B. Liang, W. Bao, and F. B. M. de Waal (1995) "The Reproductive Behavior of Golden Monkeys in Captivity." Primates 36:135-43.
      --- (1991) "The Reconciliation Behavior of Golden Monkeys (Rhinopithecus roxellanae roxellanae) in Small Breeding Groups." Primates 32:321-27.
      Schaller, G. B. (1985) "China's Golden Treasure." International Wildlife 15:29-31.
      * Yeager, C. P. (1990a) "Notes on the Sexual Behavior of the Proboscis Monkey." American Journal of Primatology 21:223-27.
      --- (1990b) "Proboscis Monkey (Nasalis larvatus) Social Organization: Group Structure." American Journal of Primatology 20:95-106.
{302}
      MACAQUES
Macaques
      JAPANEESE MACAQUES (Macaca fuscata)
IDENTIFICATION: A medium-sized (3-foot-long) monkey with a brownish gray coat, short tail, and red facial skin. DISTRIBUTION: Japan; endangered. HABITAT: Forests, including subalpine and snow-covered terrain. STUDY AREAS: Wild: near Arashiyama, Takasakiyama (Kyushu), Shiga Heights (Jigokundai), Koshima, Miyajima, and other areas of Japan; semiwild: near Laredo, Texas; the Oregon Regional Primate Research Center; captivity: Laboratory of Behavioral Primatology, St-Hyacinthe, Quebec; Calgary Zoo; Cavriglia Park (Italy).

      Social Organization
      Japanese Macaques live in cosexual troops of 20-100 individuals, subdivided into smaller matrilineal groups composed of numerous related females and several unrelated males. Males usually leave their birth group on reaching maturity and may even periodically transfer to different groups, live in all-male groups, or become solitary or peripheral. Females, in contrast, generally remain in their home group for life. As a result, the group is centered around the kinship and bonding between females (and some groups have only one regular adult male member).
     

Female Japanese Macaques in a sexual embrace. This face-to-face position is less common during heterosexual and male homosexual interactions.

      Description
      Behavioral Expression: Female Japanese Macaques form intense, exclusive pair-bonds with each other based on mutual sexual attraction. These pairings are known as CONSORTSHIPS and are characterized by a number of distinctive affectionate, sexual, and social activities. Female partners in a consortship typically sit together, huddling or in close physical contact, and often spend long periods grooming one another between their sexual interactions. They also synchronize their movements, including traveling in tandem and persistently following one {303} another, and may make cooing sounds toward one another. Consorts become agitated when another animal approaches or intrudes, responding with threats, shudders, vocalizing, or withdrawal. They sometimes actively separate themselves from their relatives (temporarily forgoing the time they would usually spend grooming their young or other kin), even occasionally withdrawing from the main troop as a whole. Partners in homosexual consortships often forge strong supportive "alliances" with each other, defending their partner and intervening on her behalf when she is threatened by another individual. Most such interventions do not disrupt the traditional hierarchy or rank system of the troop. However, some interventions are termed REVOLUTIONARY because partners challenge higher-ranking individuals, while others are ARBITRATING interventions, involving mediation between individuals with more ambiguous rankings. Females also actively compete with individuals of both sexes for access to other females as sexual partners, sometimes even incurring severe injuries when they challenge intruding males. Consortships typically last from a few days to several weeks during the mating season, although partners often develop a strong friendship as a result of a consortship and remain bonded throughout the year (in contrast to heterosexual consortships, which generally do not extend beyond the mating season). Females are often serially monogamous, forming several exclusive consortships sequentially during the mating season, although they generally have fewer partners than individuals engaging in heterosexual or male homosexual activities. Homosexual pairings occur among females of all ages, from adolescents to the very old, and sometimes an adult female will pair with a pubescent female. Interestingly, an incest taboo is in effect for homosexual but not heterosexual consortships: females never choose close relatives (mothers, sisters, daughters, granddaughters, first cousins) as partners, whereas brother-sister and mother-son consorts do occasionally occur. Aunts and nieces, however, do not generally recognize each other as kin in this species, and so they sometimes consort together.
      As signaled by the reddening of their faces and sexual skin (which also swells), females in consortships are usually "in heat," and sexual activity is a regular and prominent feature of these homosexual pairings. Females engage in a variety of behaviors that involve genital stimulation, usually in the form of one female mounting another. Fully seven different positions are used for homosexual copulation (as well as for heterosexual mating, although with different frequencies). Most commonly, one female sits or lies on the back of the other, making pelvic thrusts and rubbing her clitoris against her partner's rump. The mountee's clitoris maybe stimulated by her partner's thrusting or with her own tail. Two females also sometimes embrace each other in a face-to-face position and rub their genitals together, either lying down or "sitting in each other's lap"; these postures are more common in lesbian interactions than heterosexual ones. Other positions include the "double-foot-clasp" (one female mounts from behind, grasping her partner's ankles or thighs with her feet); rear mounts where the mounter keeps her feet on the ground; and thrusting against the partner in sideways or variable postures. During mounting, females sometimes make vocalizations such as hoarse, cackling ko-ko-ko-ko sounds. Females being mounted commonly reach back and grab their partner, gazing {304} intensely into her eyes and grimacing, while the mounter clutches the fur on her partner's back — indications that both females probably experience orgasm during homosexual interactions. Consorts usually mount each other in a series of three or more consecutive mounts (as in heterosexual mating), and mounting is often reciprocal (partners exchange positions). In addition to mounting and genital rubbing, consorts occasionally suck each other's nipples. Sexual interactions are frequently initiated by the mountee, who performs a number of characteristic "courtship" behaviors to solicit or "demand" a mount from her consort. She may slap the ground while shrieking, run away from her partner and then return while presenting her hindquarters, or else display a variety of other behaviors such as head bobbing, vocalizing, arching of the back, lip quivering, intense staring, and even spasms and more aggressive pushing and grabbing. All of these are distinct from heterosexual courtship, in which the female usually invites the male to mount by slowly inching toward him in a sitting position, with mutual flipping of ears and eyebrows. A wide variety of sounds are used in both heterosexual and homosexual courtships, including cooing, whistling, warbling, squawking, chirping, barking, and squeaking — the latter is more typical of interactions between females, however.
      Male Japanese Macaques also mount each other. They do not generally form homosexual consortships — indeed, some males mount up to 24 different partners — but some individuals do have certain preferred partners, usually of the same age. Males also sometimes engage in affectionate and playful activities in combination with their sexual interactions, including touching, huddling, and grooming. Unlike heterosexual and lesbian interactions, most mounts between males are single (rather than series) and are generally briefer, although they can still involve full erections, pelvic thrusting, penetration, and/or ejaculation. The double-foot-clasp is the preferred posture between males, and sitting or lying on the partner's back is rarely if ever used. Young males often make a distinctive purring or churring sound deep in the throat while mounting each other; this vocalization is not heard in heterosexual contexts. Sexual activity between males differs from male-female behavior in a number of other ways: homosexual mounting is more common outside or toward the end of the breeding season, while heterosexual mounts are more frequently interrupted by other individuals than mounts between males.

      Frequency: The prevalence of homosexual activity in Japanese Macaques varies greatly between different troops, although it can be found to some degree in virtually every population. In some cases, more than a quarter of all consortships are between females and up to a third or more of all mounting episodes are homosexual; five to ten mounts between males may occur each morning in some troops. In other troops, same-sex behavior is much less frequent.

      Orientation: Again, the proportion of the female population participating in homosexual activity is highly variable, ranging from 12-78 percent, averaging 43 percent (in semiwild troops). In some troops, all females that participate in same-sex consortships are bisexual, also consorting with males; however, while paired with a female they remain faithful to their partner, ignoring or rebuffing any {305} advances made by males toward them. In other troops, though, some females are exclusively lesbian, engaging in sexual interactions only with females: in these cases, an average of 9 percent of females are homosexual, 56 percent bisexual, and 35 percent exclusively heterosexual. Among males, there is a similar variation in the proportion of individuals participating in homosexual mounting, from as low as 0-15 percent, to virtually all the males in a troop. Generally, though, males that engage in same-sex activity also participate in opposite-sex mounting. Interestingly, some of the most intense homosexual activity, involving complete mounts with ejaculation, is exhibited by males who are also the most active heterosexually.

      Nonreproductive and Alternative Heterosexualities
      Nonprocreative heterosexual activities are a prominent feature of Japanese Macaque life. In some populations, as many as three-quarters of all females actively seek sexual interactions while they are pregnant, half do so while menstruating, and individual females may copulate with an average of ten different males during the mating season. Most heterosexual mounts (nearly two-thirds) do not lead to ejaculation. In addition, REVERSE mounting is common, in which a female climbs on top of a male and rubs her genitals on his back. In some troops, about 40 percent of all females engage in this behavior and it occurs in about a third of all heterosexual interactions. Masturbation is also common in both males and females. Females in some troops frequently form consortships with sexually immature (preadolescent) males; as noted above, incestuous pairings also sometimes occur, and up to 15 percent of heterosexual mountings may be between related individuals.
      Heterosexual mating occurs year round, but rarely leads to pregnancy when it takes place outside of the breeding season. Nor are females unique in experiencing a sexual cycle with distinct nonreproductive periods: males undergo a yearly seasonal fluctuation in their hormone levels that results in retraction of their testicles, cessation of ejaculation, and loss of color in their sexual skin during the nonmating season. In addition, approximately 10 percent of Japanese Macaques in some troops form nonbreeding or celibate heterosexual pairs: the partners specifically avoid sexual activities with each other, although they may interact sexually with other individuals. Many females also experience a long postreproductive period later in their lives, generally lasting four to five years and constituting about 16 percent of the average life span. Such individuals continue to be sexually active, copulating with males at rates comparable to those of breeding females and also interacting with the same number of female sexual partners as do younger females.
      In some troops, a unique form of "baby-sitting" has developed. Although males in this species do not typically participate in parenting, high-ranking males in some populations take care of infants that are not their own for short periods. They groom, carry, embrace, and protect the infants, usually with the consent of their mothers. A few females also act as baby-sitters; however, nonbreeding females have also been known to kidnap infants, sometimes keeping them permanently. In addition, a few male caretakers interact sexually with infants (usually females), masturbating themselves while carrying them or even thrusting against them.
{306}
      Sources (* asterisked references discuss homosexuality/transgender)
      * Chapais, B., C. Gauthier, J. Prud'homme, and P. Vasey (1997) "Relatedness Threshold for Nepotism in Japanese Macaques." Animal Behavior 53:1089-1101.
      * Chapais, B., and C. Mignault (1991) "Homosexual Incest Avoidance Among Females in Captive Japanese Macaques." American Journal of Primatology 23:171-83.
      * Corradino, C. (1990) "Proximity Structure in a Captive Colony of Japanese Monkeys (Macaca fuscata fuscata): An Application of Multidimensional Scaling." Primates 31:351-62.
      * Eaton, G. G. (1978) "Longitudinal Studies of Sexual Behavior in the Oregon Troop of Japanese Macaques." In T. E. McGill, D. A. Dewsbury, and B. D. Sachs, eds., Sex and Behavior: Status and Prospectus, pp. 35-59. New York: Plenum Press.
      * Enomoto, T. (1974) "The Sexual Behavior of Japanese Monkeys." Journal of Human Evolution 3:351-72.
      * Fedigan, L. M. (1982) Primate Paradigms: Sex Roles and Social Bonds. Montreal: Eden Press.
      * Fedigan, L. M., and H. Gouzoules (1978) "The Consort Relationship in a Troop of Japanese Monkeys." In D. Chivers, ed., Recent Advances in Primatology, vol. 1: pp. 493-95. London: Academic Press.
      * Gouzoules, H., and R. W. Goy (1983) "Physiological and Social Influences on Mounting Behavior of Troop-Living Female Monkeys (Macaca fuscata)." American Journal of Primatology 5:39-49.
      * Green, S. (1975) "Variation of Vocal Pattern with Social Situation in the Japanese Monkey (Macaca fuscata): A Field Study." In L. A. Rosenblum, ed., Primate Behavior: Developments in Field and Laboratory Research, vol. 4, pp. 1-102. New York: Academic Press.
      * Hanby, J. P. (1974) "Male-Male Mounting in Japanese Monkeys (Macaca fuscata)." Animal Behavior 22:836-49.
      * Hanby, J. P., and C. E. Brown (1974) "The Development of Sociosexual Behaviors in Japanese Macaques Macaca fuscata." Behavior 49:152-96.
      * Hanby, J. P., L. T. Robertson, and C. H. Phoenix (1971) "The Sexual Behavior of a Confined Troop of Japanese Macaques." Folia Primatologica 16:123-43.
      Itani, J. (1959) "Paternal Care in the Wild Japanese Monkey, Macaca fuscata fuscata." Primates 2:61-93.
      * Lunardini, A. (1989) "Social Organization in a Confined Group of Japanese Macaques (Macaca fuscata). An Application of Correspondence Analysis." Primates 30:175-85.
      * Rendall, D., and L. L. Taylor (1991) "Female Sexual Behavior in the Absence of Male-Male Competition in Captive Japanese Macaques (Macaca fuscata)." Zoo Biology 10:319-28.
      * Sugiyama, Y. (1960) "On the Division of a Natural Troop of Japanese Monkeys at Takasakiyama." Primates 2:109-48.
      * Takahata, Y. (1982) "The Socio-sexual Behavior of Japanese Monkeys." Zeitschrift fur Tierpsychologie 59:89-108.
      * --- (1980) "The Reproductive Biology of a Free-Ranging Troop of Japanese Monkeys." Primates 21:303-29.
      Takahata, Y., N. Koyama, and S. Suzuki (1995) "Do the Old Aged Females Experience a Long Postreproductive Life Span?: The Cases of Japanese Macaques and Chimpanzees." Primates 36:169-80.
      * Tartabini, A. (1978) "An Analysis of Dyadic Interactions of Male Japanese Monkeys (Macaca fuscata fuscata) in a Cage-Room Observation." Primates 19:423-36.
      Tokuda, K. (1961) "A Study on the Sexual Behavior in the Japanese Monkey Troop." Primates 3:1-40.
      * Vasey, P. L. (1998) "Female Choice and Inter-sexual Competition for Female Sexual Partners in Japanese Macaques." Behavior 135:1-19.
      * --- (1996-98) Personal communication.
      * --- (1996) "Interventions and Alliance Formation Between Female Japanese Macaques, Macaca fuscata, During Homosexual Consortships." Animal Behavior 52:539-51.
      * Vasey, P. L., B. Chapais, and C. Gauthier (1998) "Mounting Interactions Between Female Japanese Macaques: Testing the Influence of Dominance and Aggression." Ethology 104:387-98.
      * Wolfe, L. D. (1986) "Sexual Strategies of Female Japanese Macaques (Macaca fuscata)." Human Evolution 1:267-75.
      * --- (1984) "Japanese Macaque Female Sexual Behavior: A Comparison of Arashiyama East and West." In M. F. Small, ed., Female Primates: Studies by Women Primatologists, pp. 141-58. New York: Alan R. Liss.
      * --- (1979) "Behavioral Patterns of Estrous Females of the Arashiyama West Troop of Japanese Macaques (Macaca fuscata)." Primates 20:525-34.
      * Wolfe, L. D., and M. J. S. Noyes (1981) "Reproductive Senescence Among Female Japanese Macaques (Macaca fuscata fuscata)." Journal of Mammology 62:698-705.
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Macaques
      RHESUS MACAQUE (Macaca mulatta)
IDENTIFICATION: A brown monkey with a pale reddish face and rump, and a medium-sized tail (up to I foot long). DISTRIBUTION: Afghanistan, India, southern China, northern Southeast Asia. HABITAT: Variable, including semidesert, forests, swamps. STUDY AREAS: Wild: near Dehra Dun, India; semiwild: Cayo Santiago Island, Puerto Rico; captivity: Caribbean Primate Research Center, Sabana Seca, Puerto Rico; California, Tulane, Wisconsin, and Yerkes Regional Primate Research Centers; and other locations.

      Social Organization
      Rhesus Macaques live in troops numbering up to 80-100 individuals. These are composed of several cosexual subgroups (averaging around 18 members) organized along matrilineal kinship. Males typically leave their subgroup during adolescence and establish themselves elsewhere — sometimes in all-male groups — leaving the female line of descent intact.


Courtship between two female Rhesus Macaques: a game of "hide-and-seek"

      Description
      Behavioral Expression: In female Rhesus Macaques, homosexual behavior usually takes place in a CONSORTSHIP, a type of pair-bond between two females that can last anywhere from a few days to many months (consortships are also characteristic of heterosexual relations). Two consorts follow and spend a great deal of time with each other, and participate in a wide variety of courtship, affectionate, and sexual activities; consort partners also sometimes cooperate in attacking other individuals. Females might consort with several other females, although most have only one partner. Lesbian courtship is highly distinctive, and involves five different playful pursuit games: "hide-and-seek," in which two females peek at each other from around a tree trunk; "kiss and run," in which one female rushes up to another and briefly kisses or nuzzles her before running off, the other in pursuit; "follow the leader," in which the females alternate positions following one another; "lipsmack and circle," where one female circles closer and closer to the other while making lip-smacking noises; and "present and run," where one female invites the other to mount her and then teasingly runs off. {308}
      Sexual activity usually involves one female mounting the other, either in the position used for heterosexual mounting (with the mounter's feet on the mountee's legs), or in a position unique to homosexual mounting, in which one female climbs directly on the back of the other female and rubs her genitals on the mountee's rump. Mounting from the side also occurs. The mounter sometimes stimulates her clitoris or has her partner do it for her, during a mount. Both females show signs of orgasm: the mounter often "pauses" the way a male does at the moment of ejaculation, while the mountee often reaches back and clutches her partner. In some consortships the two females mount each other reciprocally, although in many cases one female is consistently the mounter and her partner always the mountee. Sometimes two females also participate in sexual hugging, in which they wrap their arms and legs around each other while one or both of them engage in clitoral stimulation (including rubbing their genitals on the ground). Combined with sexual stimulation, females also kiss (touching lips or tongues), caress each other's face, gently bite one another's ears, and groom each other. Pregnant females sometimes participate in homosexual mounting and consortships as well. Occasionally, females behave aggressively toward a female sexual partner, as also seen in heterosexual interactions (see below).
      Male Rhesus Macaques also mount each other, sometimes within a consortship as well. Mounting can include full anal penetration and ejaculation, or else simple thrusting against the partner. Sometimes the mounted male masturbates himself or his partner, and reciprocal mounting is also common (in which the two males take turns mounting each other). In some cases, one male performs a series of mounts one after the other on his partner, as in heterosexual mating. Homosexual activity may be accompanied by grooming or play-wrestling, and the two partners in a consortship can be highly affectionate toward each other, with extended periods of touching, holding, and embracing. Mounting between brothers has also been observed, as well as with males of other species such as Crab-eating Macaques (in captivity). {309}
      Several types of intersexuality occur spontaneously in Rhesus Macaques, including hermaphrodite monkeys whose internal gonads are a combination of ovaries and testes, as well as individuals that have female external genitalia but are missing a female sex chromosome and have no ovaries.

      Frequency: In wild and semiwild populations of Rhesus Macaques, anywhere from 16 percent to 47 percent of mounting is between animals of the same sex; the majority of homosexual mounting (84 percent) is between males. Within a lesbian consortship, two females may mount each other more than 200 times over six months, and one couple participated in homosexual mounting more than 1,000 times during that time.

      Orientation: Depending on the population, 20-90 percent of females participate in homosexual mounting and/or consortships. The majority of these females are bisexual, since they also engage in heterosexual activity (either concurrently or during other periods of their lives), and some even alternate between same-sex and opposite-sex activities in the same day. At least some females that are bisexual nevertheless do seem to prefer homosexual activity, since they return to their female consorts even after having mated with males; a female consort may also try to "win" her female partner back whenever she is temporarily with a male. In addition, some individuals participate in lesbian consortships more frequently than others and generally have much less contact with the opposite sex. Females may also be generally more receptive to same-sex advances: in one population, for example, only 6 percent of attempted homosexual mounts were rejected, compared to 29 percent of heterosexual attempts. Many male Rhesus Macaques are bisexual as well, and individuals vary in their participation in homosexual versus heterosexual activity. As with females, though, some individuals do seem to show a "preference" for homosexuality, since males may mount each other while ignoring available females. Moreover, in a detailed study of one male homosexual consortship or sexual "friendship" in captivity, both males preferred each other's company to that of a female and chose each other as sexual partners when given a preference test (even though both were able to perform heterosexually with a female).

      Nonreproductive and Alternative Heterosexualities
      Rhesus Macaques are noted for their nonprocreative heterosexual behaviors. Half or more of all pregnant females engage in sexual behavior (including mating), and 12 percent of all copulations involve pregnant females. Some individual males even seem to prefer mating with females after they conceive, since nearly half of their copulations are with pregnant females. In fact, parturition itself sometimes stimulates sexual activity in attendants and onlookers, who may masturbate themselves or even mount the mother shortly after she gives birth. More than 40 percent of menstruating females also engage in sexual activity. The typical pattern for heterosexual copulation includes a large number of nonreproductive mounts, since the male may mount the female up to 100 or more times as part of each "copulation." Although penetration may occur during each mount, usually only the final {310} mount in the series involves ejaculation. Females often initiate sexual behavior with males and commonly experience orgasm during heterosexual mating. They may also copulate with several different males — in fact, females typically mate with more consort partners than do males, to such an extent that they experience a phenomenon known as VAGINAL OVERFLOW because of the amount of sperm they receive from such multiple matings. Rhesus Macaque females also sometimes mount males — such REVERSE mountings can account for 2-6 percent of all heterosexual mountings. Males may become sexually stimulated while a female is mounting them, masturbating or ejaculating spontaneously, and she may also achieve orgasm from rubbing during the mount. Males often masturbate to ejaculation on their own, while females have been observed fondling and sucking their own nipples. Sexual activity with nonoptimal partners also occurs: males occasionally mount their mothers or sisters (incestuous activity accounts for 12-15 percent of all sexual interactions in some populations), and adult-juvenile sexuality (primarily mounting but also fellatio, including with infants) may account for more than 15 percent of all sexual activity. A wide range of interspecies sexual interactions in captivity have also been observed (including a female Rhesus soliciting copulations from a Dog).
      Male Rhesus Macaques have a yearly hormonal cycle with a distinct nonbreeding period. Females also commonly experience a postreproductive or "menopausal" stage later in their lives, in which they no longer breed but may still be sexually active. They may also continue to be valued members of the troop, even contributing to the care and raising of infants and juvenile monkeys. In addition, females of all ages participate in a type of "baby-sitting," in which individuals — in — cluding nonbreeding monkeys — look after infants belonging to other females (and also act as "attendants" during their births). These "aunts," as they are sometimes called (though they need not be genetically related to the mother), often protect and take care of the infants. Males (who generally do not participate in parenting) also occasionally engage in similar behavior and may even adopt orphaned infants. In some cases, though, "aunts" engage in aggressive or sexual interactions with the infants as well and may even try to "kidnap" another female's baby. Mothers are also sometimes abusive toward their own infants — shoving, biting, and stepping on the baby's head have all been observed, and one study showed that about 11 percent of infants are abused in their first two years of life. In addition, heterosexual relations are often characterized by aggression: males frequently attack and may severely wound females that they mate or consort with.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Akers, J. S., and C. H. Conaway (1979) "Female Homosexual Behavior in Macaca mulatta." Archives of Sexual Behavior 8:63-80.
      * Altmann, S. A. (1962) "A Field Study of the Sociobiology of Rhesus Monkeys, Macaca mulatta." Annals of the New York Academy of Sciences 102:338-435.
      * Carpenter, C. R. (1942) "Sexual Behavior of Free Ranging Rhesus Monkeys (Macaca mulatta). I. Specimens, Procedures, and Behavioral Characteristics of Estrus. II. Periodicity of Estrus, Homosexual, Autoerotic, and Non-Conformist Behavior." Journal of Comparative Psychology 33:113-62.
      Conaway, C. H., and C. B. Koford (1964) "Estrous Cycles and Mating Behavior in a Free-ranging Band of Rhesus Monkeys." Journal of Mammalogy 45:577-88.
      * Erwin, J., and T. Maple (1976) "Ambisexual Behavior with Male-Male Anal Penetration in Male Rhesus Monkeys." Archives of Sexual Behavior 5:9-14. {311}
      * Fairbanks, L. A., M. T. McGuire, and W. Kerber (1977) "Sex and Aggression During Rhesus Monkey Group Formation." Aggressive Behavior 3:241-49.
      * Gordon, T. P., and I. S. Bernstein (1973) "Seasonal Variation in Sexual Behavior of All-Male Rhesus Troops." American Journal of Physical Anthropology 38:221-26. *
      Hamilton, G. V. (1914) "A Study of Sexual Tendencies in Monkeys and Baboons." Journal of Animal Behavior 4:295-318.
      * Huynen, M. C. (1997) "Homosexual Interactions in Female Rhesus Monkeys, Macaca mulatta." In M. Taborsky and B. Taborsky, eds., Contributions to the XXV International Ethological Conference, p. 211. Advances in Ethology no. 32. Berlin: Blackwell Wissenschafts-Verlag.
      Kaufmann, J. H. (1965) "A Three-Year Study of Mating Behavior in a Free-Ranging Band of Rhesus Monkeys." Ecology 46:500-12.
      * Kempf, E. J. (1917) "The Social and Sexual Behavior of Infrahuman Primates With Some Comparable Facts in Human Behavior." Psychoanalytic Review 4:127-54.
      * Lindburg, D. G. (1971) "The Rhesus Monkey in North India: An Ecological and Behavioral Study." In L. A. Rosenblum, ed., Primate Behavior: Developments in Field and Laboratory Research, vol. 2, pp. 1-106. New York: Academic Press.
      Loy, J. D. (1971) "Estrous Behavior of Free-Ranging Rhesus Monkeys (Macaca mulatta)." Primates 12:1-31.
      --- (1970) "Peri-Menstrual Sexual Behavior Among Rhesus Monkeys." Folia Primatologica 13:286-97.
      Michael, R. P., M. I. Wilson, and D. Zumpe (1974) "The Bisexual Behavior of Female Rhesus Monkeys." In R. C. Friedman, ed., Sex Differences in Behavior, pp. 399-412. New York: John Wiley & Sons.
      Missakian, E. A. (1973) "Genealogical Mating Activity in Free-Ranging Groups of Rhesus Monkeys (Macaca mulatta) on Cayo Santiago." Behavior 45:225-41.
      Partch, J. (1978) "The Socializing Role of Postreproductive Rhesus Macaque Females." American Journal of Physical Anthropology 48:425.
      * Reinhardt, V., A. Reinhardt, F. B. Bercovitch, and R. W. Goy (1986) "Does Intermale Mounting Function as a Dominance Demonstration in Rhesus Monkeys?" Folia Primatologica 47:55-60.
      Rowell, T. E., R. A. Hinde, and Y. Spencer-Booth (1964) "'Aunt'-Infant Interaction in Captive Rhesus Monkeys." Animal Behavior 12:219-26.
      * Sade, D. S. (1968) "Inhibition of Son-Mother Mating Among Free-Ranging Rhesus Monkeys." In J. H. Masserman, ed., Animal and Human, pp. 18-38. Science and Psychoanalysis, vol. 12. New York: Grune & Stratton.
      Schapiro, S. J., and G. Mitchell (1983) "Infant-Directed Abuse in a Seminatural Environment: Precipitating Factors." In M. Reite and N. G. Caine, eds., Child Abuse: The Nonhuman Primate Data, pp. 29-48. Monographs in Primatology, vol.1. New York: Alan R. Liss.
      * Sullivan, D. J., and H. P. Drobeck (1966) "True Hermaphrodism in a Rhesus Monkey." Folia Primatologica 4:309-17.
      Tilford, B. (1981) "Nondesertion of a Postreproductive Rhesus Female by Adult Male Kin." Journal of Mammalogy 62:638-39.
      Vessey, S. H., and D. B. Meikle (1984) "Free-Living Rhesus Monkeys: Adult Male Interactions with Infants and Juveniles." In D. M. Taub, ed., Primate Paternalism, pp. 113-26. New York: Van Nostrand Reinhold.
      * Weiss, G., R. F. Weick, E. Knobil, S. R. Wolman, and F. Gorstein (1973) "An X-O Anomaly and Ovarian Dysgenesis in a Rhesus Monkey." Folia Primatologica 19:24-7.
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Macaques
      STUMPTAIL MACAQUE (Macaca arctoides)
IDENTIFICATION: A medium-sized (2-foot-long) monkey with dark or reddish brown fur, a short, almost hairless tail, and mottled black-and-red skin on the face. DISTRIBUTION: Southeast Asia and south-central China; vulnerable. HABITAT: Dense forests, including mountainous regions. STUDY AREAS: Semiwild: island of Toto-gochillo, Lake Catemaco, Mexico; captivity: Stanford University; University of Helsinki; the Netherlands Primate Center; Yerkes and Wisconsin Regional Primate Research Centers; Calcutta and Paris Zoos.

      Social Organization
      Few field studies of Stumptail Macaques have been conducted, so little is known of their social organization in the wild. They generally appear to live in cosexual groups of 20-50 individuals with a matrilineal organization. The mating system is probably polygamous or promiscuous, involving copulations with multiple partners and little male parental involvement.


Two male Stumptail Macaques in mutual fellatio

      Description
      Behavioral Expression: Male Stumptails form intense sexual "friendships" with each other, within which an extraordinary variety of homosexual activities are expressed. One male may develop strong affectionate bonds with another male, as shown by their embracing, gently nibbling at each other's mouth, and huddling together. The two partners may even sleep together, one closely hugging the other from behind while holding his partner's penis. The affection between these males is also expressed through sexual activity, ranging from mounting to oral sex to mutual masturbation. Mounting occurs in the typical front-to-back position found in heterosexual mating; pelvic thrusting, anal penetration, and occasionally ejaculation can all be components of this activity. Fellatio or oral-genital activity involves one male licking or sucking on the penis of the other for up to two minutes at a time. This is done in a variety of positions, for example with one male behind the other or mounted on him, sucking his genitals between his legs. The males may even perform mutual fellatio in a 69 position. Males also fondle one another's scrotum and penis, rubbing the hand up and down the shaft; again, a number of positions are used — one male may stand sideways in front of another who is sitting down, {313} spreading his thighs to allow the seated male to masturbate him, or they may engage in mutual masturbation by backing up toward each other and fondling each other's genitals between their legs. Sometimes male Stumptails also sit together and masturbate themselves, stimulated by the sight of one another or of a nearby heterosexual mating. The partners in a sexual friendship may be of the same age, or one may be considerably younger than the other, perhaps even an infant.
      Female Stumptails also form sexual friendships with one another. These relationships, which involve a considerable amount of affectionate behavior as well, may be a stable association between just two females, or they may be more fluid, involving a network of three females, for example, or more short-lived pairings. Sexual behavior involves mounting with intense genital stimulation and orgasm. One female will climb onto the back of her favorite partner, using a position slightly different from heterosexual mating that allows her to rub her genitals against the rump of the other female. This may also be accomplished in a front-to-back sitting position, one female pulling the other up against her belly, and the two may even end up lying or leaning back together in this configuration. Lesbian interactions are prolonged, lasting up to two minutes (a duration similar to heterosexual mating), and the females usually make numerous pelvic thrusts comparable to the amount performed by a male in a heterosexual mounting. Orgasm is striking: the mounting female tenses up, first pausing and then showing a number of body spasms; her fur stands on end, and this is combined with a characteristic frowning and round-mouthed facial expression (also found in ejaculating males) and rapid breathing sounds. She also experiences a number of intense uterine contractions lasting for nearly a minute. The female being mounted does {314} not, apparently, have the same sort of orgasmic response, although she is in a state of high sexual arousal, and will often reach back to clutch the mounting female and even kiss her during the climax. Following orgasm, the females usually hug one another and make teeth-chattering or squeaking sounds. In some cases females can apparently reach orgasm without direct genital stimulation, particularly when they are hugging their favorite female partner in great excitement after being reunited.


A female Stumptail Macaque kissing her female partner at the climax of mounting

      Frequency: Homosexual activity is common in Stumptail Macaques, accounting for as much as 25-40 percent of all sexual encounters in some captive and semi-wild groups. In one study, nearly two-thirds of this same-sex activity was between females, while in another population, all same-sex mounting was between males.

      Orientation: Most Stumptail females are probably simultaneously bisexual, interspersing heterosexual activity with homosexual activity. In fact, females have been known to participate in lesbian activities when they are lactating (and possibly even during pregnancy), indicating an easy compatibility between motherhood and homosexuality in this species. Some males show a decrease in the intensity of their same-sex friendships as they get older and may begin engaging in a larger proportion of heterosexual activity as they mature. Nevertheless, most males probably continue to have some homosexual contact throughout their lives.


Male Stumptail Macaques manually stimulating each other's genitals. Mutual or reciprocal sexual behaviors such as this are good examples of homosexual activity that is not "dominance" oriented.

      Nonreproductive and Alternative Heterosexualities
      Male Stumptails engage in both masturbation and nonreproductive heterosexual mating. In the latter case, males have been observed mounting females without full penetration, mating with menstruating females, rubbing their genitals on the female (sometimes to ejaculation), and even stimulating the penis with their own foot while mounted on the female. Both male and female orgasm can be a component of heterosexual mating. Sometimes, however, mating is distinctly less pleasurable — especially for the female, who may collapse under the weight of the male during copulation (he may be up to twice as heavy as she is). Females are also sometimes bitten by males during mounting, resulting in shallow cuts on her shoulders and upper arms (this occurs in about 15-18 percent of copulations). More than half of all matings involve male aggression (including chasing the female, pushing or pulling her, and fighting or biting her) and/or female resistance (including running away from the male, screaming, trying to dislodge him, and fighting with him). In addition, heterosexual copulations are often harassed by other individuals (of both sexes), sometimes in spectacular outbursts of activity that involve an entire social group. This often occurs following ejaculation while the two mating animals remain attached in a "copulatory tie," similar to that of mating Dogs.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Bernstein, I. S. (1980) "Activity Patterns in a Stumptail Macaque Group (Macaca arctoides)." Folia Primatologica 33:20-45.
      * Bertrand, M. (1969) The Behavioral Repertoire of the Stumptail Macaque: A Descriptive and Comparative Study. Bibliotheca Primatologica 11. Basel: S. Karger. {315}
      * Chevalier-Skolnikoff, S. (1976) "Homosexual Behavior in a Laboratory Group of Stumptail Monkeys (Macaca arctoides): Forms, Contexts, and Possible Social Functions." Archives of Sexual Behavior 5:511-27.
      * --- (1974) "Male-Female, Female-Female, and Male-Male Sexual Behavior in the Stumptail Monkey, with Special Attention to the Female Orgasm." Archives of Sexual Behavior 3:95-116.
      * Estrada, A., and R. Estrada (1978) "Changes in Social Structure and Interactions After the Introduction of a Second Group in a Free-ranging Troop of Stumptail Macaques (Macaca arctoides): Social Relations II." Primates 19:665-80.
      * Estrada, A., R. Estrada, and F. Ervin (1977) "Establishment of a Free-ranging Colony of Stumptail Macaques (Macaca arctoides): Social Relations I." Primates 18:647-76.
      * Goldfoot, D. A., H. Westerborg-van Loon, W. Groeneveld, and A. K. Slob (1980) "Behavioral and Physiological Evidence of Sexual Climax in the Female Stump-tailed Macaque (Macaca arctoides)." Science 208:1477-79.
      Gouzoules, H. (1974) "Harassment of Sexual Behavior in the Stumptail Macaque, Macaca arctoides." Folia Primatologica 22:208-17.
      * Leinonen, L., I. Linnankoski, M.-L. Laakso, and R. Aulanko (1991) "Vocal Communication Between Species: Man and Macaque." Language and Communication 11:241-62.
      * Linnankoski, I., and L. M. Leinonen (1985) "Compatibility of Male and Female Sexual Behavior in Macaca arctoides." Zeitschrift fur Tierpsychologie 70:115-22.
      Niemeyer, C. L., and A. S. Chamove (1983) "Motivation of Harassment of Matings in Stumptailed Macaques." Behavior 87:298-323.
      * O'Keefe, R. T., and K. Lifshitz (1985) "A Behavioral Profile for Stumptail Macaques (Macaca arctoides)." Primates 26:143-60.
      * Slob, A. K., and P. E. Schenk (1986) "Heterosexual Experience and Isosexual Behavior in Laboratory-Housed Male Stump-tailed Macaques (M. arctoides)." Archives of Sexual Behavior 15:261-68.
      * de Waal, F. B. M. (1989) Peacemaking Among Primates. Cambridge, Mass.: Harvard University Press.
      de Waal, F. B. M., and R. Ren (1988) "Comparison of the Reconciliation Behavior of Stumptail and Rhesus Macaques." Ethology 78:129-42.
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Macaques
      BONNET MACAQUE (Macaca radiata)
IDENTIFICATION: A grayish brown monkey with a circular "cap" of hair on the head, a prominent wrinkled brow and forehead, and a long tail (over 2 feet in males). DISTRIBUTION: Southern India. HABITAT: Forests, scrub, open areas. STUDY AREAS: Near Somanathapur Sandal Reserve and Byrankuppe (Mysore State), Dharwar, Karnataka (Tamil Nadu), and Lal Bagh (Bangalore), India; California Primate Research Center; State University of New York; subspecies M.r. diluta.
      CRAB-EATING MACAQUE (Macaca fascicularis)
IDENTIFICATION: A gray-green to reddish brown monkey with a slight pointed crest, pinkish face, and long tail. DISTRIBUTION: Southeast Asia including Indonesia, Philippines, Nicobar Islands, and introduced to Palau. HABITAT: Forests, swamps. STUDY AREAS: Angaur Island, Palau, Micronesia; Yerkes Regional Primate Research Center; University of California — Berkeley.

      Social Organization
      Both Bonnet and Crab-eating Macaques live in fairly large matriarchal groups containing numerous adult males and females as well as youngsters; males typically emigrate from their home group on becoming adults. Bonnet groups can be as large as 50-60 monkeys, but most average around 18-20 individuals, with four or five each of adult males and females. Male Bonnets demonstrate a strong tendency to interact and cooperate with one another, often forming supportive COALITIONS together. Crab-eating Macaques live in troops containing 40-50 individuals on average; smaller groups each contain 2-9 adult males. Large subgroups of youngsters, as well as some peripheral or solitary animals, also occur.


Two male Bonnet Macaques embracing each other in a "greeting" gesture. The male on the left is fondling the scrotum of the other male with his right hand, an activity also found in male Savanna Baboons, where it is known as "diddling."

      Description
      Behavioral Expression: Male Bonnet Macaques frequently mount one another, using the same front-to-back position found in heterosexual copulation. A male may have anywhere from two to five different partners that he mounts; each male also varies in the proportion of times he mounts or is mounted. One male acted as the mountee in only 9 percent of his homosexual mountings, another did so in all of his mountings, though the average is a roughly equal proportion of {317} mounter-mountee behavior, and reciprocal mounting occurs as well. In addition, male Bonnets engage in a wide variety of other same-sex behaviors, both affectionate and sexual, often within a coalition "bond" between them. Masturbation of another male is common in all age groups, especially younger males — one male holds or fondles the other's penis and may even eat the semen from the resulting ejaculation (mutual masturbation also occurs). Males also sometimes grip and gently tug on each other's scrotum; often, this is accompanied by embracing, nuzzling, grasping of the rump, tongue-clicking, and mouthing of the other's neck or shoulders, all combined into a sort of ritualized "greeting" interaction. Another behavior, unique to homosexual interactions, involves two males rhythmically rubbing their rumps and genital areas together, often reaching back between their legs to fondle each other's genitals. This behavior also occurs between females, as does mounting.
      Homosexual mounting also occurs in male Crab-eating Macaques. In addition, male Crab-eaters may mouth and fondle the genitals and anal region of another male, including using their index finger to investigate the area. Males can also develop intense sexual friendships with one another, especially between older and younger males. In one such pair observed in captivity, affectionate embraces frequently led to sexual arousal and homosexual mounting, often accompanied by excited lip-smacking or crooning sounds; the male being mounted sometimes even turned his head to kiss his partner during a mount. Both consensual and nonconsensual mounting occurs in Crab-eating Macaques — in the former (54 percent of mounts between males), the mounted animal fully cooperates by standing still and helps support the weight of the other male (and perhaps even initiates the encounter). In nonconsensual mounts (46 percent of mounts between males), the mounting animal may corner his partner and hold him down (this also occurs in heterosexual mounting). Male Crab-eaters also occasionally engage in homosexual contact with other species. Wild Crab-eating Macaques sometimes allow male Orang-utans to perform fellatio on them, while in captivity they have been known to attempt copulation with males of a number of nonprimate species, including foxes.


An older male Bonnet Macaque in India mounting a younger male
{318}
      Frequency: Homosexual mounting is very common in male Bonnet Macaques. In some populations, same-sex mounts exceed the number of heterosexual mounts by as much as four to one, and mounting between males can comprise 31 percent to 79 percent of all mounting. Sexual and affectionate behaviors between males occur in about a quarter of their interactions with one another. Female homosexual activity is somewhat less common: one study found that mounting between females occurred at rates that were two to seven times less than male-female or male-male mounting, although the rates of mutual rump rubbing with genital stimulation between females were only slightly less than between males. In Crab-eating Macaques, homosexual mounting accounts for 17-30 percent of mountings, and 10 percent of all interactions between males involve mounting (compared to nearly 50 percent of all interactions between males and females).

      Orientation: Nearly all male Bonnet Macaques participate in both homosexual and heterosexual mounting, but it appears that they generally have more different male partners than female ones. Some males participate very little in homosexual activity (accounting for about 10 percent of the same-sex mountings in a population), while others may be involved in more than half of all homosexual mounts. A similar variation occurs with respect to their heterosexual participation. However, males that are the least active heterosexually are not necessarily the most active homosexually: in many cases, those males that participate in a large number of homosexual mountings also have a large number of heterosexual mountings. No quantitative information on sexual orientation is available for Crab-eaters; however, observations in captivity indicate that males engage in both homosexual and heterosexual copulation, sometimes alternating relatively frequently between the two. Furthermore, males that are "bonded" to one another show a preference for their partner that even survives separation and intervening heterosexual activity. If such males are separated from one another, they rush to embrace each other on being reunited, resuming their sexual relationship where they left off.

      Nonreproductive and Alternative Heterosexualities
      As noted above, heterosexual matings in Crab-eating Macaques are not always consensual: about 19 percent of such mounts are forced by the male on the female. Furthermore, male Crab-eaters sometimes severely attack females with small babies and also occasionally kill those infants to gain sexual and breeding access to the female. Both Bonnets and Crab-eaters participate in a range of nonprocreative sexual behaviors. Among Crab-eaters, females copulate during pregnancy (though usually not during the first two to three weeks), while more than half of male-female copulations do not involve ejaculation. In both species, females have multiple male partners and copulations — during one six-month period, for example, each female Crab-eater mated an average of 45 times, with some copulating more than 110 times. Female Bonnets may mate with up to three different males in succession, and females also sometimes mount males (REVERSE mounting). Male Bonnet Macaques may also manually penetrate females, inserting a finger and then {319} licking or smelling it. Unlike in a number of other primates, in Bonnets this behavior does not appear to be simply a way of testing the sexual receptivity of the female. Both male and female Bonnets also masturbate, females sometimes employing innovative techniques (such as using objects or pulling their tail between their legs and using it to rub their labia while making pelvic thrusting movements). Crab-eating Macaques engage in an interesting form of "infidelity": heterosexual mating typically occurs within a short-term bond or consortship. However, nearly 20 percent of all copulations in some populations are nonmonogamous: half of all females and almost three-quarters of the males "steal" matings with other partners during a consortship, but return to their original partner afterward. The social system of Bonnet Macaques may entail considerable inbreeding, and incestuous mother-son matings that produce viable offspring do occur.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Bernstein, S. (1970) "Primate Status Hierarchies." In L. A. Rosenblum, ed., Primate Behavior: Developments in Field and Laboratory Research, vol. 1, pp. 71-109. New York: Academic Press.
      Emory, G. R., and S. J. Harris (1978) "On the Directional Orientation of Female Presents in Macaca fascicularis." Primates 19:227-29.
      * Hamilton, G. V. (1914) "A Study of Sexual Tendencies in Monkeys and Baboons." Journal of Animal Behavior 4:295-318.
      * Kaufman, I. C., and L. A. Rosenblum (1966) "A Behavioral Taxonomy for Macaca nemestrina and Macaca radiata: Based on Longitudinal Observation of Family Groups in the Laboratory." Primates 7:205-58.
      * Makwana, S. C. (1980) "Observations on Population and Behavior of the Bonnet Monkey, Macaca radiata." Comparative Physiology and Ecology 5:9-12.
      Moore, J., and R. Ali (1984) "Are Dispersal and Inbreeding Avoidance Related?" Animal Behavior 32:94-112.
      * Nolte, A. (1955) "Field Observations on the Daily Routine and Social Behavior of Common Indian Monkeys, with Special Reference to the Bonnet Monkey (Macaca radiata Geoffroy)." Journal of the Bombay Natural History Society 53:177-84.
      Noordwijk, M. A. van (1985) "Sexual Behavior of Sumatran Long-tailed Macaques (Macaca fascicularis)." Zeitschrift fur Tierpsychologie 70:277-96.
      * Poirier, F. E., and E. O. Smith (1974) "The Crab-Eating Macaques (Macaca fascicularis) of Angaur Island, Palau, Micronesia." Folia Primatologica 22:258-306.
      Rahaman, H., and M. D. Parthasarathy (1969) "Studies on the Social Behavior of Bonnet Monkeys." Primates 10:149-62.
      * --- (1968) "The Expressive Movements of the Bonnet Macaque." Primates 9:259-72.
      * Rasmussen, D. R. (1984) "Functional Alterations in the Social Organization of Bonnet Macaques (Macaca radiata) Induced by Ovariectomy: An Experimental Analysis." Psychoneuroendocrinology 9:343-74.
      * Silk, J. B. (1994) "Social Relationships of Male Bonnet Macaques: Male Bonding in a Matrilineal Society." Behavior 130:271-92.
      --- (1993) "Does Participation in Coalitions Influence Dominance Relationships Among Male Bonnet Macaques?" Behavior 126:171-89.
      Sinha, A. (1997) "Complex Tool Manufacture by a Wild Bonnet Macaque, Macaca radiata." Folia Primatologica 68:23-25.
      * Simonds, P. E. (1996) Personal communication.
      * --- (1965) "The Bonnet Macaque in South India." In I. DeVore, ed., Primate Behavior: Field Studies of Monkeys and Apes, pp. 175-96. New York: Holt, Rinehart, & Winston.
      * Sugiyama, Y. (1971) "Characteristics of the Social Life of Bonnet Macaques (Macaca radiata)." Primates 12:247-66.
      * Thompson, N. S. (1969) "The Motivations Underlying Social Structure in Macaca irus." Animal Behavior 17:459-67.
      * --- (1967) "Some Variables Affecting the Behavior of Irus Macaques in Dyadic Encounters." Animal Behavior 15:307-11.
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Macaques
      PIG-TAILED MACAQUE (Macaca nemestrina)
IDENTIFICATION: A medium-sized monkey (up to 30 pounds in males) with olive-brown fur and a short, curly, nearly naked tail. DISTRIBUTION: Southeast Asia from Burma to Sumatra; vulnerable. HABITAT: Forests. STUDY AREAS: Near Mt. Kerinci, West Sumatra, Indonesia, subspecies M.n. nemestrina; Bernam River, western Malaysia; Washington and Yerkes Regional Primate Research Centers; State University of New York; Turin Zoo.
      CRESTED BLACK MACAQUE (Macaca nigra)
IDENTIFICATION: An entirely black monkey with a striking crest, long muzzle, high cheek and brow ridges, and a short tail. DISTRIBUTION: Sulawesi, Indonesia; endangered. HABITAT: Tropical forest. STUDY AREAS: Tangkoko-DuaSudara Nature Reserve, North Sulawesi, Indonesia; Oregon and Yerkes Regional Primate Research Centers; Woodland Park Zoological Gardens, Seattle, Washington.

      Social Organization
      Both of these species live in cosexual groups, containing 15-40 individuals in Pigtails and up to 40-90 individuals in Crested Black Macaques. Pig-tailed groups are matrilineal clans, in which females remain in their home (natal) group while males emigrate on reaching maturity. The heterosexual mating system is promiscuous: both sexes mate with multiple partners. Smaller Crested Black Macaque groups (6-15 individuals) may contain only one adult male.


Two female Crested Black Macaques masturbating each other

      Description
      Behavioral Expression: Pig-tailed Macaques engage in homosexual mounting as well as kissing. Male Pigtails mount each other using the posture found in heterosexual mating (one male behind the other, hands grasping the loins, and feet clasping the calves of the other), sometimes with erection of the penis and pelvic thrusting (though anal penetration does not occur). Females use the same position and also occasionally thrust against their female partner; the mounting female is usually in heat. Some Pigtails engage in same-sex mounting with only one partner, while other Pigtails have several partners (as many as seven for females, though the average is three). Individuals differ as to whether they prefer mounting or being {321} mounted in homosexual encounters: a few animals engage in only one or the other, while most exhibit a range of mounter/mountee behavior. Males may even mount each other reciprocally, exchanging positions in different mounting sessions. Same-sex kissing (mouth-to-mouth contact) occurs more often than heterosexual kissing and is most common between females. However, many female homosexual mounts are "forced" in the sense that the animal being mounted does not solicit the mounting, and aggression may also be involved: 48 percent of mounts between females are nonconsensual, compared to 18 percent of heterosexual ones. No mounts between males are forced. Some same-sex mounting is incestuous, e.g., between mother and daughter or siblings of either sex.
      Crested Black Macaques also participate in male and female homosexual mounting, similar in many ways to that found in Pigtails. Females often reach back to clasp the leg of a female mounting them, which is believed to be a sign of orgasm (it also occurs in heterosexual mounting), while males being mounted by other males frequently fondle their own penis. Mounting is sometimes preceded by a gesture of invitation known as REAR-END FLIRTATION, in which one male walks by another and presents his hindquarters. Younger males often mount older ones in this species. A number of other homosexual activities occur in Crested Black Macaques. Females engage in a form of mutual masturbation unique to homosexual interactions, in which they stand side by side facing in opposite directions (draping an arm over the other's waist) and fondle and sniff each other's vulva, sometimes with direct clitoral stimulation. Males often participate in a form of erotic grooming: one male uses his hands, lips, and tongue to groom the other, who usually has an erection and may masturbate himself by rolling his penis between his palms or licking it (he usually eats his own semen if he ejaculates). The grooming animal is often sexually aroused, too, as evidenced by his erection. Males (especially younger ones) also use a number of ritualized erotic "greeting" gestures with one another, including embracing, face-licking or kissing, fondling or grabbing of the erect penis, mounting, and rump fingering.

      Frequency: Same-sex mounting occurs frequently in Pig-tailed Macaques, accounting for 7-23 percent of all mounting activity. More than three-quarters of all kissing occurs between females. In Crested Black Macaques, about 5-8 percent of all mounting activity occurs between males. Ritualized penis-grabbing or fondling between males takes place regularly {322} in this species and can be observed weekly, and perhaps even daily, in some wild populations.

      Orientation: Most Pig-tailed Macaques are probably bisexual, engaging in both same- and opposite-sex mounting. However, individuals vary along a continuum of what percentage of their activity is homosexual: for some males, it is as little as 8 percent, while for others, nearly two-thirds of their mounting activity is same-sex. Although less specific information is available for Crested Black Macaques, they appear to have a similar orientation profile: in one wild troop, for example, all males participated in both heterosexual and homosexual mounting (as well as penis-grabbing) to varying degrees.

      Nonreproductive and Alternative Heterosexualities
      As noted above, some heterosexual copulations in Pig-tailed Macaques are forced, in that the female is an unwilling participant. Furthermore, more than a third of aggressive interactions in Pigtails are between males and females (73 percent are directed by the male against the female). Infanticide has also been seen among captive Pigtails — in some cases, infants as young as one day old have died from head and neck injuries inflicted by adult males. In addition, a 33 — year study of this species (spanning seven generations and nearly 400 individuals) found that one in eight infants is physically abused or neglected by its mother. This includes being dragged across the ground, having its fingers or tail chewed, suffering severe eye damage or blindness as a result of compulsive grooming around the eyes, having its head or body crushed on the ground, and/or being rejected, abandoned, or starved by its mother. Physical abuse accounts for about a third of all Pigtail infant injuries or deaths; it appears to run in families and is usually repeated with successive offspring. Infants can also be injured when they are kidnapped, which occurs only occasionally and is typically carried out by a nonbreeding female.
      A number of nonreproductive sexual behaviors occur in these two species as well. In Pigtails, males mount nonovulating females 8-15 percent of the time, and 1-2 percent of heterosexual behavior involves females mounting males (REVERSE mounts). In addition, female Pigtails may mate with up to five different males during a single period of heat. Mother-son mountings occur as well. In both of these species, heterosexual mounting sometimes does not involve penetration: nearly a fifth of Crested Black male-female mounts, for example, are "ritualized" or non-copulatory. Male Pigtails and Crested Black Macaques also masturbate, occasionally eating their own semen, while female Crested Black Macaques sometimes masturbate by inserting a finger into the vagina and simultaneously slapping their rump with one hand. Infant and very young male Crested Blacks often mount adult females, performing pelvic thrusts and even achieving penetration. Finally, spontaneous abortions occur among Pigtails, often associated with a number of physiological changes in the female's blood chemistry: one study in captivity found that 14 percent of pregnancies terminated in abortions (among females not otherwise at high risk for miscarriages).
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      Other Species
      Homosexual mounting occurs in three other species of Macaques: Lion-tailed (Macaca silenus), Tonkean (Macaca tonkeana), and Moor (Macaca maurus) Macaques. In the latter two species, 11-13 percent of mounting activity is same-sex.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Bernstein, I. S. (1972) "Daily Activity Cycles and Weather Influences on a Pigtail Monkey Group." Folia Primatologica 18:390-415.
      * --- (1970) "Primate Status Hierarchies." In L. A. Rosenblum, ed., Primate Behavior: Developments in Field and Laboratory Research, vol.1, pp. 71-109. New York: Academic Press.
      * --- (1967) "A Field Study of the Pigtail Macaque (Macaca nemestrina)." Primates 8:217-28.
      Bernstein, I. S., and S. C. Baker (1988) "Activity Patterns in a Captive Group of Celebes BlackApes (Macaca nigra)." Folia Primatologica 51:61-75.
      * Bound, V., H. Shewman, and J. Sievert (1988) "The Successful Introduction of Five Male Lion-tailed Macaques (Macaca silenus) at Woodland Park Zoo." In AAZPA Regional Conference Proceedings, pp. 122-31. Wheeling, W.Va.: American Association of Zoological Parks and Aquariums.
      * Caldecott, J. 0. (1986) An Ecological and Behavioral Study of the Pig-Tailed Macaque. Basel: Karger.
      * Dixson, A. F. (1977) "Observations of the Displays, Menstrual Cycles, and Sexual Behavior of the 'Black Ape' of Celebes (Macaca nigra)." Journal of Zoology, London 182:63-84.
      * Giacoma, C., and P. Messeri (1992) "Attributes and Validity of Dominance Hierarchy in the Female Pigtail Macaque." Primates 33:181-89.
      * Kaufman, I. C., and L. A. Rosenblum (1966) "A Behavioral Taxonomy for Macaca nemestrina and Macaca radiata: Based on Longitudinal Observation of Family Groups in the Laboratory." Primates 7:205-58.
      Kyes, R. C., R. E. Rumawas, E. Sulistiawati, and N. Budiarsa (1995) "Infanticide in a Captive Group of Pigtailed Macaques (Macaca nemestrina):" American Journal of Primatology 36:135-36.
      Maestripieri, D., K. Wallen, and K. A. Carroll (1997) "Infant Abuse Runs in Families of Group-Living Pigtail Macaques." Child Abuse and Neglect 21:465-71.
      * Matsumura, S., and K. Okamoto (1998) "Frequent Harassment of Mounting After a Takeover of a Group of Moor Macaques (Macaca maurus)." Primates 39:225-30.
      * Nickelson, S. A., and J. S. Lockard (1978) "Ethogram of Celebes Monkeys (Macaca nigra) in Two Captive Habitats." Primates 19:437-47.
      Oi, T. (1996) "Sexual Behavior and Mating System of the Wild Pig-tailed Macaque in West Sumatra." In J. E. Fa and D. G. Lindburg, eds., Evolution and Ecology of Macaque Societies, pp. 342-68. Cambridge: Cambridge University Press.
      * --- (1991) "Non-copulatory Mounting of Wild Pig-tailed Macaques (Macaca nemestrina nemestrina) in West Sumatra, Indonesia." In A. Ehara, T. Kimura, O. Takenaka, and M. Iwamoto, eds., Primatology Today, pp. 147-50. Amsterdam: Elsevier Science Publishers.
      * --- (1990a) "Patterns of Dominance and Affiliation in Wild Pig-tailed Macaques (Macaca nemestrina nemestrina) in West Sumatra." International Journal of Primatology 11:339-55.
      --- (1990b) "Population Organization of Wild Pig-tailed Macaques (Macaca nemestrina nemestrina) in West Sumatra." Primates 31:15-31.
      * Poirier, F. E. (1964) "The Communicative Matrix of the Celebes Ape (Cynopithecus niger): A Study of Sixteen Male Laboratory Animals." Master's thesis, University of Oregon.
      * Reed, C. (1997) Personal communication.
      * Reed, C., T. G. O'Brien, and M. F. Kinnaird (1997) "Male Social Behavior and Dominance Hierarchy in the Sulawesi Crested Black Macaque (Macaca nigra)." International Journal of Primatology 18:247-60.
      Schiller, H. S., G. P. Sackett, W. T. Frederickson, and L. J. Risler (1983) "Maintenance of High-density Lipoprotein Blood Levels Prior to Spontaneous Abortion in Pig-tailed Macaques (Macaca nemestrina)." American Journal of Primatology 4:127-33.
      * Skinner, S. W., and J. S. Lochard (1979) "An Ethogram of the Liontail Macaque (Macaca silenus) in Captivity." Applied Animal Ethology 5:241-53.
      * Thierry, B. (1986) "Affiliative Interference in Mounts in a Group of Tonkean Macaques (Macaca tonkeana)." American Journal of Primatology 11:89-97.
      * Tokuda, K., R. C. Simons, and G. D. Jensen (1968) "Sexual Behavior in a Captive Group of Pigtailed Monkeys (Macaca nemestrina)." Primates 9:283-94.
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      OTHER PRIMATES
Baboons
      SAVANNA BABOON (Papio cynocephallus)
IDENTIFICATION: The familiar baboon, with variable coat color (greenish to yellowish brown to grayish black), doglike head with a black face, and long tail (over 2 feet in males). DISTRIBUTION: Equatorial, eastern, and southern Africa. HABITAT: Scrub, savanna, woodland. STUDY AREAS: Gombe Stream National Park, Tanzania; Ishasha Forest and Queen Elizabeth National Park, Uganda; Amboseli National Park, and near Gilgil and the Athi River, Kenya; Cape of Good Hope Nature Reserve, South Africa; Namibia; subspecies P.c. anubis, the Olive Baboon; P.c. ursinus, the Chacma Baboon; and P.c. cynocephalus, the Yellow Baboon.
      HAMADRYAS BABOON (Papio hamadryas)
IDENTIFICATION: A gray baboon with a striking silver-gray "cape" or shoulder mane in adult males. DISTRIBUTION: Somalia, Ethiopia, southern Saudi Arabia, Yemen. HABITAT: Semidesert, steppe, savanna woodlands, rocky terrain. STUDY AREAS: Erer-Gota region, eastern Ethiopia; Brookfield (Illinois) and London Zoos.
      GELADA BABOON (Theropithecus gelada)
IDENTIFICATION: A brown baboon with a thick "cape" of fur in adult males; both sexes have an hourglass-shaped patch of bare skin on the chest, encircled by fleshy "beads" in estrous females. DISTRIBUTION: Northern and central Ethiopia. HABITAT: Mountain grasslands, rocky gorges. STUDY AREAS: Simien Mountain National Park, Ethiopia; Yerkes Regional Primate Research Center, Georgia; San Antonio Zoo, Texas.
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      Social Organization
      Savanna Baboons live in groups of 30-100 containing both adult males and females. Females form the matriarchal core of each group since they remain for life, whereas males often emigrate to a new group on reaching adulthood. However, some troops are strongly inbred because individuals rarely leave. In contrast, both Gelada and Hamadryas Baboons live in large troops that include so-called HAREM groups — bands that have a single male and several females. In Geladas, the primary social bonds are between the females in such groups (most of whom are related to each other, as in Savanna Baboons), whereas in Hamadryas Baboons the primary bonds are between the male and the females. Unlike many other primates, Hamadryas females emigrate from the group while males remain (hence, most of the females in a group are not related to each other). Geladas also have "bachelor" troops of nonbreeding males, and "bachelor" Hamadryas or Gelada males sometimes associate with a harem group and may develop a close relationship with its male leader.


Mounting between two male Savanna Baboons in Tanzania

      Description
      Behavioral Expression: Homosexual mounting among both males and females occurs in all three of these Baboon species. The position used is similar to that for heterosexual copulation: the mounting animal places its hands on the mountee's lower back and clasps the mountee's ankles or thighs with its feet. Both sexes often make pelvic thrusts during homosexual mounts; males usually have an erection, and ejaculation does occur in at least some Savanna Baboon mounts between males. Male Savanna Baboons also sometimes fondle their own or their partner's genitals during a same-sex mount, and male mounters may gently bite or nuzzle their partner's neck after a homosexual mount. Male Geladas have also been observed masturbating other males. Females of these species mount each other both during "heat" and outside of their sexual cycle; about 9 percent of lesbian mounts in Savanna Baboons involve a pregnant female mounting another female. Because most Savanna and Gelada females are related to the other females in a troop, at least some homosexual activity is incestuous.
      In Savanna Baboons, homosexual mounting occurs in a variety of contexts, including during good-natured play-fighting. However, in this species (and to some extent also in the other species) same-sex mounting is most prominent as {326} part of a unique form of male "greeting" interaction. Whenever two males meet each other, they exchange a series of ritualized sexual behaviors that may include homosexual mounting and invitations to mount, as well as a wide variety of other sexual and affectionate contacts. One such behavior is known as DIDDLING, in which the males fondle each other's genitals, including touching or pulling on the penis and fondling the scrotum. Males also embrace and kiss each other on the head or mouth, and may even bend down to kiss, lick, or nibble on another male's penis or nuzzle his groin and thighs. Sometimes a male will also nuzzle another male's back with his nose, especially during a mount. Another "greeting" behavior involves one male patting, grabbing, and sometimes even nuzzling or fingering another male's rear end. Although most "greeting" interactions are relatively brief and one-sided, occasionally two males develop a closer, bonded relationship sometimes known as a COALITION, in which the "greeting" interactions are more extensive, frequent, and reciprocated. Partners in such an alliance take turns exchanging sexual behaviors with each other (especially diddling), and they often protect and help one another. Such coalitions between males may become stable, long-lasting associations that persist for many years.
      Several different kinds of intersexual or hermaphrodite individuals occur spontaneously in Savanna Baboons. In South African populations, gender-mixing individuals sometimes become high-ranking and powerful members of their troops. Such animals have female genitalia and internal organs, yet their mammary glands are not developed. Genetically, they are male (having XY chromosomes), physically they are large — exceeding the proportions of nonintersexed females and sometimes even males — and sexually, they often interact with males. Another type of intersexuality found in Baboons involves animals that have male external genitals (including testes) combined with some female internal reproductive organs (such as a uterus and fallopian tubes).


A male Savanna Baboon in southern Africa nuzzling the genitals of another male

      Frequency: Among Savanna Baboons, homosexual activity is common: 13-24 percent of all mounting behavior is between males and up to 9 percent is between females. "Greetings" interactions — which include ritualized homosexual activities — occur more than twice as often as any other form of interaction between {327} males and take place roughly once every 50 minutes in some troops. Approximately 10 percent of males in some areas develop closely bonded coalitions, which comprise about 2 percent of all dyads between males. In Hamadryas Baboons, sexual behavior (homosexual or heterosexual) is overall less frequent, but approximately one-third to two-thirds of sexual activity may occur between animals of the same sex (mostly between males). In a study of wild Geladas, homosexual interactions between males were observed about once every two hours; in captivity, 14-25 percent of mounts are between males and 2-3 percent are between females.

      Orientation: In Savanna Baboons, the entire male population participates in homosexual "greetings" interactions; all adult males (including those in bonded coalitions with other males) are sexually active with females as well, indicating a high degree of bisexuality. This is probably true to a lesser extent for females, not all of whom engage in homosexual mounting. In Hamadryas Baboons, harem-holding males may be bisexual, mounting both males and females, while Gelada harem males are usually exclusively heterosexual (although they may engage in same-sex genital handling if there is another male in the troop). Some "bachelor" males in both species may engage solely in homosexual activity, especially adolescents and younger adults. In Geladas, for example, an average of 12 percent of the population lives in all-male groups (where same-sex activity usually occurs). In some areas this proportion is as high as 40 percent or more, although most such males do eventually breed.

      Nonreproductive and Alternative Heterosexualities
      A large proportion of Baboon heterosexual behavior involves nonprocreative activities. Savanna and Hamadryas Baboons commonly mate when the female cannot get pregnant. In some Savanna populations, up to 18 percent of heterosexual copulations occur during the nonfertilizable stages of her ovulatory cycle (including during menstruation) and 2-12 percent of matings happen when the female is already pregnant. Most females, however, remain abstinent while pregnant or lactating and in fact are (hetero)sexually active for less than 10 percent of their adult lives. Heterosexual mountings do not always involve penetration and/or ejaculation, either — in fact, one study found that less than 40 percent of opposite-sex matings in Savanna Baboons involved "full" copulation. Moreover, a variety of sexual behaviors besides vaginal intercourse occur, including fondling of genitals and females mounting males (REVERSE mounts). Masturbation is also a component of Baboon sexual expression, with several innovative techniques employed: Savanna males stimulate the penis with their hand, lick their own penis, rub their genitals against the ground, or stroke the penis with the tip of the tail, while females stimulate the clitoris and perineal area with the tail or fingers. Both males and females show evidence of sexual arousal during grooming, in the form of rhythmic erection of the genitals — "penis flicking" in males, and labial and clitoral swelling and "pulsation" in females. Sexual activity in Baboons also sometimes includes copulation with partners that are not optimal for breeding: adult male Savanna Baboons and adult female Hamadryas Baboons may mate with juvenile animals, incestuous {328} matings are common in inbred troops, while "friendships" and sexual behavior between Baboons and Common Chimpanzees have been observed in the wild (and between female Savanna Baboons and male Macaques in captivity). In addition, infertile females are occasionally found in Savanna Baboons — in one troop they constituted 10 percent of all the adult females — and these individuals continue to engage in sexual behavior.
      Several other forms of nonbreeding are found among Baboons. Geladas and Hamadryas Baboons, for example, have significant "bachelor" populations that do not generally participate in reproduction (constituting 20 percent of the male Hamadryas population). Older female Savanna Baboons sometimes experience a postreproductive period, while breeding-age males and females in this species often form platonic "friendships" with each other. Sexual relations in Baboons, however, are sometimes characterized by significant antagonism and even violence between the sexes. Hamadryas harem males often threaten and attack females, biting them on the neck to prevent them from leaving the group. Adult male Savanna Baboons sometimes rape younger females, often seriously injuring them, and adult females avoid or refuse a third of all mating attempts by males. In some populations, abortions and infanticide result when an outside male takes over a troop. He viciously attacks both mothers and infants to maximize his breeding opportunities; as a result of this brutality, females may suffer severe injuries as well as miscarriages, and infants may be killed. There is also evidence that females attack other females in order to suppress their reproduction. Infanticide was recently discovered among Geladas as well. Many male Baboons act as "baby-sitters" for infants, although occasionally the youngsters become injured during fights between their "baby-sitter" (or "kidnapper") and other males.

      Other Species
      Homosexual activity occurs in several other species of African monkeys. Same-sex mounting (in both males and females) is found in Vervets (Cercopithecus aethiops) (comprising about 11 percent of all mounting), Sooty Mangabeys (cercocebus torquatus) (about 18 percent of mounting), and Talapoins (Miopithecus talapoin). Mounting between male Vervets is often accompanied by grooming, embracing from behind, fondling and displaying of the genitals, and nuzzling of the perineum and scrotum. Same-sex mounting in Talapoins may also include embracing or play-wrestling. Among Patas Monkeys (Erythrocebus patas), adolescent and younger males often fondle and nuzzle the scrotum and genitals of adult males.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Abegglen, J.-J. (1984) On Socialization in Hamadryas Baboons: A Field Study. Lewisburg, Pa.: Bucknell University Press.
      * Bernstein, I. S. (1975) "Activity Patterns in a Gelada Monkey Group." Folia Primatologica 23:50-71.
      * --- (1970) "Primate Status Hierarchies." In L. A. Rosenblum, ed., Primate Behavior: Developments in Field and Laboratory Research, vol.l, pp. 71-109. New York: Academic Press.
      * Bielert, C. (1985) "Testosterone Propionate Treatment of an XY Gonadal Dysgenetic Chacma Baboon." Hormones and Behavior 19:372-85.
      * --- (1984a) "The Social Interactions of Adult Conspecifics with an Adult XY Gonadal Dysgenetic Chacma Baboon (Papio ursinus)." Hormones and Behavior 18:42-55. {329}
      * --- (1984b) "Estradiol Benzoate Treatment of an XY Gonadal Dysgenetic Chacma Baboon." Hormones and Behavior 18:191-205.
      * Bielert, C., R. Bernstein, G. B. Simon, and L. A. van der Walt (1980) "XY Gonadal Dysgenesis in a Chacma Baboon (Papio ursinus)." International Journal of Primatology 1:3-14.
      * Dixson, A. F., D. M. Scruton, and J. Herbert (1975) "Behavior of the Talapoin Monkey (Miopithecus talapoin) Studied in Groups, in the Laboratory." Journal of Zoology, London 176:177-210.
      Dunbar, R. (1984) Reproductive Decisions: An Economic Analysis of Gelada Baboon Social Strategies. Princeton: Princeton University Press.
      * Dunbar, R., and P. Dunbar (1975) Social Dynamics of Gelada Baboons. Basel: S. Karger.
      * Fedigan, L. M. (1972) "Roles and Activities of Male Geladas (Theropithecus gelada)." Behavior 41:82-90.
      * Gartlan, J. S. (1974) "Adaptive Aspects of Social Structure in Eryhthrocebus patas." In S. Kondo, M. Kawai, A. Ehara, and S. Kawamura, eds., Proceedings from the Symposia of the Fifth Congress of the International Primatological Society, pp. 161-71. Tokyo: Japan Science Press.
      * --- (1969) "Sexual and Maternal Behavior of the Vervet Monkey, Cercopithecus aethiops." Journal of Reproduction and Fertility, supplement 6:137-50.
      * Hall, K. R. L. (1962) "The Sexual, Agonistic, and Derived Social Behavior Patterns of the Wild Chacma Baboon, Papio ursinus." Proceedings of the Zoological Society of London 139:283-327.
      * Hausfater, G., and D. Takacs (1987) "Structure and Function of Hindquarter Presentations in Yellow Ba boons (Papio cynocephalus)." Ethology 74:297-319.
      * Kummer, H. (1968) Social Organization of Hamadryas Baboons. Chicago: University of Chicago Press.
      * Kummer, H., and F. Kurt (1965) "A Comparison of Social Behavior in Captive and Wild Hamadryas Baboons." In H. Vagtborg, ed., The Baboon in Medical Research, pp. 65-80. Austin: University of Texas Press.
      * Leresche, L. A. (1976) "Dyadic Play in Hamadryas Baboons." Behavior 57:190-205.
      * Marais, E. N. (1926) "Baboons, Hypnosis, and Insanity." Psyche 7:104-10.
      * --- (1922/1969) The Soul of the Ape. New York: Atheneum.
      * Maxim, P. E., and J. Buettner-Janusch (1963) "A Field Study of the Kenya Baboon." American Journal of Physical Anthropology 21:165-80.
      Mori, A., T. Iwamoto, and A. Bekele (1997) "A Case of Infanticide in a Recently Found Gelada Population in Arsi, Ethiopia." Primates 38:79-88.
      * Mori, U. (1979) "Individual Relationships within a Unit; Development of Sociability and Social Status." In M. Kawai (ed.) Ecological and Sociological Studies of Gelada Baboons, pp. 93-154. Basel: S. Karger.
      * Noe, R. (1992) "Alliance Formation Among Male Baboons: Shopping for Profitable Partners." In A. H. Harcourt and F. B. M. de Waal, eds., Coalitions and Alliances in Humans and Other Animals, pp. 284-321. Oxford: Oxford University Press.
      * Owens, N. W. (1976) "The Development of Sociosexual Behaviour in Free-Living Baboons, Papio anubis." Behavior 57:241-59.
      Packer, C. (1980) "Male Care and Exploitation of Infants in Papio anubis." Animal Behavior 28:512-20.
      Pereira, M. E. (1983) "Abortion Following the Immigration of an Adult Male Baboon (Papio cynocephalus)." American Journal of Primatology 4:93-98.
      * Ransom, T. W. (1981) Beach Troop of the Gombe. Lewisburg, Pa.: Bucknell University Press; London and Toronto: Associated University Presses.
      * Rowell, T. E. (1973) "Social Organization of Wild Talapoin Monkeys." American Journal of Physical Anthropology 38:593-98.
      * --- (1967a) "Female Reproductive Cycles and the Behavior of Baboons and Rhesus Macaques." In S. A. Altmann, ed., Social Communication Among Primates, pp. 15-32. Chicago: University of Chicago Press.
      " --- (1967b) "A Quantitative Comparison of the Behavior of a Wild and a Caged Baboon Group." Animal Behavior 15:499-509.
      Saayman, G. S. (1970) "The Menstrual Cycle and Sexual Behavior in a Troop of Free Ranging Chacma Baboons (Papio ursinus)." Folia Primatologica 12:81-110.
      Smuts, B. B. (1987) "What Are Friends For?" Natural History 96(2):36-45.
      --- (1985) Sex and Friendship in Baboons. New York: Aldine.
      * Smuts, B. B., and J. M. Watanabe (1990) "Social Relationships and Ritualized Greetings in Adult Male Baboons (Papio cynocephalus anubis)." International Journal of Primatology 11:147-72.
      * Struhsaker, T. T. (1967) Behavior of Vervet Monkeys (Cercopithecus aethiops). University of California Publications in Zoology, vol. 82. Berkeley: University of California Press.
      * Wadsworth, P. F., D. G. Allen, and D. E. Prentice (1978) "Pseudohermaphroditism in a Baboon (Papio anubis)." Toxicology Letters 1:261-66. {330}
      Wasser, S. K., and S. K. Starling (1988) "Proximate and Ultimate Causes of Reproductive Suppression Among Female Yellow Baboons at Mikumi National Park, Tanzania." American Journal of Primatology 16:97-121.
      * Weinrich, J. D. (1980) "Homosexual Behavior in Animals: A New Review of Observations From the Wild, and Their Relationship to Human Sexuality." In R. Forleo and W. Pasini, eds., Medical Sexology: The Third International Congress, pp. 288-95. Littleton, Mass.: PSG Publishing.
      * Wolfheim, J. H., and T. E. Rowell (1972) "Communication Among Captive Talapoin Monkeys (Miopithecus talapoin)." Folia Primatologica 18:224-55.
      * Zuckerman, S. (1932) The Social Life of Monkeys and Apes. New York: Harcourt, Brace and Company.

New World Monkeys
      (Common) SQUIRREL MONKEY (Saimiri sciureus)
IDENTIFICATION: A small (9-14 inch) monkey with a long tail; a pinkish white, heart- or skull-shaped facial pattern; and dense, yellowish or gray-green fur. DISTRIBUTION: Throughout most of northeastern South America, including Brazil, Colombia. HABITAT: Forests, swamps. STUDY AREAS: Monkey Jungle, Miami, Florida; Washington and California Regional Primate Research Centers; University of California — Santa Barbara; Max-Planck Institute of Psychiatry, Munich, Germany.
      RUFOUS-NAPED TAMARIN (Saguinus geoffroyi)
IDENTIFICATION: A squirrel-sized monkey with a mottled black and golden coat, a reddish tail and head, and a white crown. DISTRIBUTION: Northwestern Colombia through central Panama and Costa Rica. HABITAT: Tropical forests. STUDY AREA: Barro Colorado Island, Panama.

      Social Organization
      Squirrel Monkeys live in troops of 20-70 animals containing a majority of females. Younger males leave their home troops and live for several years in all-male "bachelor" bands of 2-10 monkeys, after which they join the cosexual troops as peripheral members. Females generally remain in their home troops for life, where they develop strong bonds with each other. Rufous-naped Tamarins live in cosexual {331} groups of 3-9 individuals in which usually only one male-female pair breeds; the remainder of the group consists of their offspring and unrelated adult nonbreeders.


A female Squirrel Monkey mounting another female

      Description
      Behavioral Expression: Female Squirrel Monkeys court and mount each other. Homosexual courtship is initiated by one female facing the other, tilting her head, and making a "purring" noise (a series of soft, guttural clicklike sounds). This may be accompanied by a GENITAL DISPLAY, in which the soliciting female positions herself in front of the other, spreading her thighs to expose her vulva and engorged or erect clitoris. As an invitation to the other female to mount, she turns around and presents her hindquarters, looking over her shoulder with her feet spread apart. This may be repeated several times, the presenting female moving away each time as the other female approaches in a sort of courtship "chase." Mounting is done in the same position used for heterosexual mating: one female grasps the other's waist with her hands and her calves with her feet, making thrusting movements with her pelvis. The mounted female frequently purrs during the sexual interaction. Sometimes two females take turns mounting each other, but often one female is more typically a mounter and the other a mountee.
      Female Squirrel Monkeys may develop a short, consortlike bond (also seen in heterosexual interactions) during which they interact sexually with one another. In addition, a number of other types of female bonding occur in this species. Females frequently have one close female "friend" with whom they travel and rest; often this relationship develops into a highly affectionate one and may even include coparenting. The two females frequently touch hands, kiss each other on the mouth, and huddle together. If one of them is a mother, the other helps her raise her infant; if both are mothers, they help each other with parenting, including nuzzling and carrying each other's infant and protecting them from predators. Often the infant develops a strong bond with the comother, although some females act as coparents for infants belonging to several different mothers. The coparenting female is sometimes known as an "aunt," although she need not be genetically related to the mother; her relationship with the mother often outlasts the duration of parenting. {332}
      Homosexual mounting sometimes occurs between male Squirrel Monkeys, especially younger individuals or between an older and a younger (adult) partner; adult males also perform the genital display to each other. During intense displays, one male will thrust his erect penis into the face of the other male while holding him down with his hands and may even climb onto the back of the other male (who also sometimes develops an erection). Several males can be drawn into the activity, forming a ball or "pileup" of three or four individuals all twisting and climbing on one another as they try to perform genital displays.
      In Rufous-naped Tamarins, homosexual behavior takes the form of same-sex mounting, including pelvic thrusting (as in heterosexual copulation); both males and females participate in homosexual mounts.


A male Squirrel Monkey (right) performing a "genital display" toward another male

      Frequency: In captivity, homosexual mounting can occur quite frequently in both mixed-sex and single-sex groups of Squirrel Monkeys: one study recorded mounts between females roughly once every 40 minutes, with homosexual activity taking place over three to seven days each month. An average of about 40 percent of genital displays occur between animals of the same sex; more than one-quarter are between females. In Rufous-naped Tamarins, homosexual mounting occurs sporadically.

      Orientation: Some female Squirrel Monkeys that bond with other females as coparents are themselves nonbreeders; to this extent, then, they are involved exclusively in same-sex activities. Most other Squirrel Monkeys, as well as Rufous-naped Tamarins, that participate in homosexual behavior are probably simultaneously bisexual. In a group of three Squirrel Monkeys (two females and one male) whose sexual activities were briefly sampled, for example, heterosexual and homosexual encounters alternated continuously for a half hour, and more than 25 percent of the courtship and sexual activities were between the females. However, no detailed long-term studies have been conducted to verify the extent of individuals' same-sex versus opposite-sex activity throughout their entire lives.


The kiss: two female Squirrel Monkeys
{333}
      Nonreproductive and Alternative Heterosexualities
      In addition to the female coparenting arrangement described above, other alternative family configurations and nonbreeding individuals occur in Squirrel Monkeys. One female sometimes adopts another female's infant, raising it along with her own baby, while some male Squirrel Monkeys never copulate at all during the mating season. Interestingly, these may be the highest-ranking males in the troop, who are often more aggressive and less patient than other males and therefore more likely to disturb females or fail to attract willing mates. Several other aspects of Squirrel Monkey heterosexual life reveal considerable antagonism and separation between the sexes. Females often form groups or COALITIONS during the mating season to chase off males who are pursuing unwilling females; females (and occasionally males) may also directly disrupt heterosexual copulations in progress. At other times, females persistently harass males so that they remain spatially segregated from the females, either on the periphery of the troop or closer to the ground. When a willing female is found and the sexual interaction is not disturbed, often several males will participate, all joining in by kissing the female on the mouth, displaying their genitals, and sniffing or nuzzling her genitalia. The mating system is promiscuous, as both males and females copulate with multiple partners.
      A number of nonprocreative sexual activities are also found in these New World monkeys. Male Squirrel Monkeys masturbate by either sucking their own penis or rubbing it with one or both hands, while females may copulate when not in heat or during pregnancy (up to the fourth month). In addition, females sometimes produce a vulvar plug from sloughed vaginal cells when they are in heat, which may serve to limit inseminations. Rufous-naped Tamarin males on occasion mount females without thrusting or penetration. Male Squirrel Monkeys also have a pronounced sexual cycle: for three to four months out of the year, they are sexually active, more aggressive, and develop a characteriscic appearance — heavier, with more fluffed fur — during which time they are known as FATTED MALES. For the remainder of the year, however, their testes are essentially dormant; they lose their "fatted" appearance and live largely separate from the females. In Rufous-naped Tamarins, as in other tamarins and marmosets, all but the highest-ranking female in a group forgo reproduction, perhaps through a complex mechanism of "self-restraint" that is mediated by pheromones from the lead female. As a result, only about half of all mature females actually reproduce at one time; however, nonbreeding individuals often continue to copulate. In addition, most matings outside the breeding season do not result in offspring, and it is thought that many embryos may be reabsorbed, aborted, or the young die soon after birth.

      Other Species
      Same-sex activity occurs in several other species of Central and South American monkeys. Homosexual mounting (in both males and females), including pelvic thrusting and genital rubbing on the partner, has been observed in a variety of Tamarin species, including the Saddle-back Tamarin (Saguinus fuscicollis), the Mustached Tamarin (S. mystax), and the Cotton-top Tamarin (S. oedipus). Both {334} male and female Lion Tamarins (Leontopithecus rosalia) sometimes mount their own offspring of both sexes, including adolescents and younger individuals. Approximately 1 percent of mounting activity in Common Marmosets (Callithrix jac-chus) occurs among adolescent and younger males (brothers living in the same family group). In White-fronted Capuchin Monkeys (Cebus albifrons), young males occasionally suck and fondle the scrotum of older males, while homosexual activity among females (including mounting) also occurs in Brown Capuchins (C. apella) and Weeper Capuchins (C. olivaceous). More than half of all mounting in White-faced Capuchins (C. capucinus) is between same-sex partners, often preceded by a type of courtship activity known as WHEEZE DANCING, involving contorted postures, wheezing vocalizations, and "slow-motion" chases.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Akers, J. S., and C. H. Conaway (1979) "Female Homosexual Behavior in Macaca mulatta." Archives of Sexual Behavior 8:63-80.
      * Anschel, S., and G. Talmage-Riggs (1978) "Social Structure Dynamics in Small Groups of Captive Squirrel Monkeys." In D. J. Chivers and J. Herbert, eds., Recent Advances in Primatology, vol. 1, pp. 601-4. New York: Academic Press.
      * Baldwin, J. D. (1969) "The Ontogeny of Social Behavior of Squirrel Monkeys (Saimiri sciureus) in a Seminatural Environment." Folia Primatologica 11:35-79.
      --- (1968) "The Social Behavior of Adult Male Squirrel Monkeys (Saimiri sciureus) in a Seminatural Environment." Folia Primatologica 9:281-314.
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      * Castell, R., and B. Heinrich (1971) "Rank Order in a Captive Female Squirrel Monkey Colony." Folia Primatologica 14:182-89.
      Dawson, G. A. (1976) "Behavioral Ecology of the Panamanian Tamarin, Saguinus oedipus (Callitrichidae, Primates)." Ph.D. thesis, Michigan State University.
      * Defler, T. R. (1979) "On the Ecology and Behavior of Cebus albifrons in Eastern Colombia: II. Behavior." Primates 20:491-502.
      * Denniston, R. H. (1980) "Ambisexuality in Animals." In J. Marmor, ed., Homosexual Behavior: A Modern Reappraisal, pp. 25-40. New York: Basic Books.
      * DuMond, F. V. (1968) "The Squirrel Monkey in a Seminatural Environment." In L. A. Rosenblum and R. W. Cooper, eds., The Squirrel Monkey, pp. 87-145. New York: Academic Press.
      DuMond, F. V., and T. C. Hutchinson (1967) "Squirrel Monkey Reproduction: The 'Fatted' Male Phenomenon and Seasonal Spermatogenesis." Science 158:1067-70.
      * Hoage, R. J. (1982) Social and Physical Maturation in Captive Lion Tamarins, Leontopithecus rosalia rosalia (Primates: Callitrichidae). Smithsonian Contributions to Zoology no. 354. Washington, D.C.: Smithsonian Institution Press.
      Hopf, S., E. Hartmann-Wiesner, B. Kuhlmorgen, and S. Mayer (1974) "The Behavioral Repertoire of the Squirrel Monkey (Saimiri)." Folia Primatologica 21:225-49.
      Latta, J., S. Hopf, and D. Ploog (1967) "Observation of Mating Behavior and Sexual Play in the Squirrel Monkey (Saimiri sciureus)." Primates 8:229-46.
      * Linn, G. S., D. Mase, D. LaFrancois, R. T. O'Keeffe, and K. Lifshitz (1995) "Social and Menstrual Cycle Phase Influences on the Behavior of Group-Housed Cebus apella." American Journal of Primatology 35:41-57.
      * Manson, J. H., S. Perry, and A. R. Parish (1997) "Nonconceptive Sexual Behavior in Bonobos and Capuchins." International Journal of Primatology 18:767-86.
      * Mendoza, S. P., and W. A. Mason (1991) "Breeding Readiness in Squirrel Monkeys: Female-Primed Females are Triggered by Males." Physiology & Behavior 49:471-79.
      Mitchell, C. L. (1994) "Migration Alliances and Coalitions Among Adult Male South American Squirrel Monkeys (Saimiri sciureus)." Behavior 130:169-90. {335}
      * Moynihan, M. (1970) Some Behavior Patterns of Platyrrhine Monkeys. II. Saguinus geoffroyi and Some Other Tamarins. Smithsonian Contributions to Zoology no. 28. Washington, D.C.: Smithsonian Institution Press.
      * Perry, S. (1998) "Male-Male Social Relationships in Wild White-faced Capuchins, Cebus capucinus." Behavior 135:139-72.
      Peters, M. (1970) "Mouth to Mouth Contact in Squirrel Monkeys (Saimiri sciureus)." Zeitschrift fur Tierpsychologie 27:1009-10.
      Ploog, D. W. (1967) "The Behavior of Squirrel Monkeys (Saimiri sciureus) as Revealed by Sociometry, Bioa-coustics, and Brain Stimulation." In S. Altmann, ed., Social Communication Among Primates, pp. 149 — 84. Chicago: University of Chicago Press.
      * Ploog, D. W., J. Blitz, and F. Ploog (1963) "Studies on the Social and Sexual Behavior of the Squirrel Monkey (Saimiri sciureus)." Folia Primatologica 1:29-66.
      Ploog, D. W., and P. D. Maclean (1963) "Display of Penile Erection in Squirrel Monkey (Saimiri sciureus)." Animal Behavior 11:32-39.
      Rosenblum, L.A. (1968) "Mother-Infant Relations and Early Behavioral Development in the Squirrel Monkey." In L. A. Rosenblum and R. W. Cooper, eds., The Squirrel Monkey, pp. 207-33. New York: Academic Press.
      * Rothe, H. (1975) "Some Aspects of Sexuality and Reproduction in Groups of Captive Marmosets (Callithrix jacchus)." Zeitschrift fur Tierpsychologie 37:255-73.
      * Shadle, A. R., E. A. Mirand, and J. T. Grace Jr. (1965) "Breeding Responses in Tamarins." Laboratory Animal Care 15:1-10.
      Skinner, C. (1985) "A Field Study of Geoffroy's Tamarin (Saguinus geoffroyi) in Panama." American Journal of Primatology 9:15-25.
      Snowdon, C. T. (1996) "Infant Care in Cooperatively Breeding Species." Advances in the Study of Behavior 25:643-89.
      Srivastava, P. K., F. Cavazos, and F. V. Lucas (1970) "Biology of Reproduction in the Squirrel Monkey (Saimiri sciureus): I. The Estrus Cycle." Primates 11:125-34.
      * Talmage-Riggs, G., and S. Anschel (1973) "Homosexual Behavior and Dominance in a Group of Captive Squirrel Monkeys (Saimiri sciureus)." Folia Primatologica 19:61-72.
      * Travis, J. C., and W. N. Holmes (1974) "Some Physiological and Behavioral Changes Associated with Oestrus and Pregnancy in the Squirrel Monkey (Saimiri sciureus)." Journal of Zoology, London 174:41 — 66.
      * Vasey, P. L.(1995) "Homosexual Behavior in Primates: A Review of Evidence and Theory." International Journal of Primatology 16:173-204.
{336}
Lemurs and Bushbabies
      VERREAUX'S SIFAKA (Propithecus verreauxi)
IDENTIFICATION: A long-legged lemur with a plush white coat, black face, black or brown crown and underparts, and long tail (nearly 2 feet). DISTRIBUTION: Western and southern Madagascar; vulnerable. HABITAT: Forests. STUDY AREA: Near Hazafotsy, Madagascar; subspecies P.v. verreauxi.
      LESSER BUSHBABY (Galago moholi)
IDENTIFICATION: A small, squirrel-like primate (7 inches, plus a foot-long tail) with silky, grayish-yellow fur, a broad face, and enormous eyes and ears. DISTRIBUTION: Sub-Saharan Africa. HABITAT: Woodland, savanna, scrub. STUDY AREA: Witwatersrand University, South Africa.

      Social Organization
      Verreaux's Sifakas live in cosexual groups of up to 12 individuals and sometimes associate as male-female pairs. As in most Lemurs, females are generally dominant to males in this species. Females typically remain in their birth group for life, while males leave their group on maturing and transfer between groups several times throughout their lives. The mating system has elements of POLYGYNANDRY, that is, females generally mate with more than one male and vice versa. Lesser Bushbabies generally live in family groups consisting of females and their offspring along with peripheral males. They are often found singly or in pairs and may form sleeping groups of up to seven individuals.

      Description
      Behavioral Expression: Male Verreaux's Sifakas sometimes mount other males during the mating season. The mounted animal — usually a younger adult or adolescent male — often snaps at the mounter and tries to wriggle free (as do females trying to escape from unwelcome heterosexual advances). In Lesser Bushbabies, females occasionally mount and thrust against each other when in heat. Like other species of Bushbabies, the genitals of female Lesser Bushbabies are unusual in several respects. The clitoris is long and pendulous, greatly resembling the male's penis, and the urethra extends through to the tip of the organ, so that females urinate through the clitoris rather than through a urethral opening near the vagina. {337} Females do not menstruate, and in fact the vagina remains closed at all times except during the mating season (which lasts no more than two to three weeks and occurs twice a year).

      Frequency: Homosexual mounting probably occurs only occasionally in Ver-reaux's Sifakas and Lesser Bushbabies. However, one study of wild Verreaux's Sifakas found that 3 out of 21 mountings (14 percent) were between males.

      Orientation: Lemurs and Bushbabies that participate in same-sex mounting probably also engage in heterosexual activity, although too little is known about individual life histories in these species to draw any firm conclusions.

      Nonreproductive and Alternative Heterosexualities
      Many heterosexual copulations in Verreaux's Sifakas — more than two-thirds in some populations — do not involve penetration or ejaculation, often because the female resists the mating attempt and wriggles free. Females sometimes also mate when they are not in heat: for some individuals, 30-80 percent of their sexual activity is nonprocreative, taking place during times when they cannot conceive. In some populations females also delay reproducing for several years, and only slightly more than half of all adult females reproduce each year. Infanticide occurs occasionally in this species, and possibly also abortions. In Lesser Bushbabies, heterosexual copulations can be lengthy — more than nine minutes in some cases — and a female often bites the male, "boxes" him with her hands, and tries to push him off or get away from him during mating.

      Sources (* asterisked references discuss homosexuality/transgender)
      * Andersson, A. B. (1969) "Communication in the Lesser Bushbaby (Galago senegalensis moholi)." Master's thesis, Witwatersrand University.
      Bearder, S. K., and G. A. Doyle (1974) "Field and Laboratory Studies of Social Organization in Bushbabies (Galago senegalensis)." Journal of Human Evolution 3:37-50.
      Brockman, D. K., and P. L. Whitten (1996) "Reproduction in Free-Ranging Propithecus verreauxi: Estrus and the Relationship Between Multiple Partner Matings and Fertilization." American Journal of Physical Anthropology 100:57-69.
      Butler, H. (1967) "The Oestrus Cycle of the Senegal Bush Baby (Galago senegalensis senegalensis) in the Sudan." Journal of Zoology, London 151:143-62.
      Dixson, A. F. (1995) "Sexual Selection and the Evolution of Copulatory Behavior in Nocturnal Prosimians." In L. Alterman, G. A. Doyle, and M. K. Izard, eds., Creatures of the Dark: The Nocturnal Prosimians, pp. 93-118. New York: Plenum Press.
      * Doyle, G. A. (1974a) "Behavior of Prosimians." Behavior of Nonhuman Primates 5:154-353.
      --- (1974b) "The Behavior of the Lesser Bushbaby." In R. D. Martin, G. A. Doyle, and A. C. Walker, eds., Prosimian Biology, pp. 213-31. Pittsburgh: University of Pittsburgh Press.
      Doyle, G. A., A. Pelletier, and T. Bekker (1967) "Courtship, Mating, and Parturition in the Lesser Bushbaby (Galago senegalensis moholi) Under Semi-Natural Conditions." Folia Primatologica 7:169-97.
      Kubzdela, K. S., A. F. Richard, and M. E. Pereira (1992) "Social Relations in Semi-Free-Ranging Sifakas (Propithecus verreauxi verreauxi) and the Question of Female Dominance." American Journal of Primatology 28:139-45.
      Lipschitz, D. L. (1996) "Male Copulatory Patterns in the Lesser Bushbaby (Galago moholi) in Captivity." International Journal of Primatology 17:987-1000.
      Lowther, F. D. L. (1940) "A Study of the Activities of a Pair of Galago senegalensis moholi in Captivity, Including the Birth and Postnatal Development of Twins." Zoologica 25:433-65. {338}
      Richard, A., (1992) "Aggressive Competition Between Males, Female-Controlled Polygyny, and Sexual Monomorphism in a Malagasy Primate, Propithecus verreauxi." Journal of Human Evolution 22:395-406.
      --- (1978) Behavioral Variation: Case Study of a Malagasy Lemur. Lewisburg, Pa.: Bucknell University Press.
      * --- — (1974a) "Intra-specific Variation in the Social Organization and Ecology of Propithecus verreauxi." Folia Primatologica 22:178-207.
      * --- (1974b) "Patterns of Mating in Propithecus verreauxi verreauxi." In R. D. Martin, G. A. Doyle, and A. C. Walker, eds., Prosimian Biology, pp. 49-74. London: Duckworth; Pittsburgh: University of Pittsburgh Press.
      Richard, A., P. Rakotomanga, and M. Schwartz (1991) "Demography of Propithecus verreauxi at Beza Ma-hafaly, Madagascar: Sex Ratio, Survival, and Fertility, 1984-1988." American Journal of Physical Anthropology 84:307-22.
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