Biological Exuberance: Animal Homosexuality and Natural Diversity

another male. This paired association resembles the temporary (from a few hours to several days) monogamous bond formed between males and females during the rutting season. In a homosexual tending, one male closely follows and defends another male and may mount him as well. In some pairs mounting is reciprocal; in others, only one partner mounts or is mounted. In addition, younger males sometimes form “tending groups” of four to five individuals who take turns mounting one another or the same individual. Homosexual tending groups are unique in the joint participation of all the males in sexual activity: although several males often accompany heterosexual tending pairs, they never participate in sexual activity with either member of the pair.

Among American Bison, various types of intersexuality or hermaphroditism occasionally occur spontaneously in nature. Some transgendered individuals are known as BUFFALO ox and grow to be extraordinarily tall—they may be one and a half times bigger than a nontransgendered bull and generally have shorter fur as well. Other intersexual individuals are intermediate in size between males and females, possess malelike horns, and have female external genitalia and a uterus combined with testes. During tending bonds, these animals interact with both males and females: one individual tended females the way a (heterosexual) male would, but was also tended by other bulls as in heterosexual and homosexual interactions.

Frequency: Homosexual mounting is very prevalent among American Bison bulls, especially during the rutting season, when it may be seen several times a day. In fact, homosexual mounting is more common than heterosexual mounting in this species, since each female rarely mates with a male more than once a year, while each male may engage in same-sex mounting many times a day. The behavior is especially frequent among younger males, peaking in three-year-olds. Studies of semiwild populations have found that more than 55 percent of mounting in younger males is same-sex, and for some age categories all mounting behavior may be homosexual. It is less common among older adult males and three-to-four-year-olds. Female homosexual mounting in Bison and African Buffalo, as well as male same-sex mounting in African Buffalo, occurs occasionally.

Orientation: In American (and probably also European) Bison, younger bulls—nearly two-thirds of the male population—are functionally bisexual, although many actually participate exclusively in homosexual activity. It was once thought that such males only engage in homosexual mounting because older bulls prevent their access to females; however, studies on captive herds have shown that bulls still participate extensively in homosexual activity even when older bulls are not present. Older bulls, as well as females in Wisent and African Buffalo, are probably functionally bisexual but primarily heterosexual, with many individuals never engaging in homosexual activity.

Nonreproductive and Alternative Heterosexualities

As noted above, large portions of the Bison bull population do not breed: males of both the American and European species are sexually mature by the time they are three years old, yet they do not get a chance to breed until they are six and large enough to compete with older males. Even among older bulls, more than a quarter do not copulate heterosexually during the rutting period, and as many as 15 percent of females may not breed in a given year. In Wisent and African Buffalo, there are some postreproductive males and females as well—older individuals who have ceased breeding in the later years of their life. Nonprocreative sexual activities also figure in the social lives of heterosexual Bison: female American Bison often mount the male during tending, for example, and male Wisent occasionally ejaculate by rubbing the penis against the female’s flanks. More than 20 percent of American Bison females engage in repeated copulations (only a single mating is necessary for procreation), and Wisent females have been observed mating with the same male eight times within half an hour. Wisent females also occasionally copulate during pregnancy (as late as three to four days before birth), and heterosexual activity sometimes occurs outside the breeding season. In American Bison, a notable separation and even hostility often exists between the sexes. As mentioned above, males and females live apart from one another for most of the year; during the rutting season, females frequently refuse the advances of males, and females often bear the scars of repeated heterosexual matings (described above). Wisent family life is occasionally marked by violence or abuse: calves have been killed by rutting bulls, and females sometimes desert their calves (especially those born late in the calving season).

Other Species

Among feral Water Buffalo (Bubalus bubalis) in Australia, female homosexual mounting is common: all cows mount other cows in heat, with 15–20 percent of the female population participating at any given time.

Sources

*asterisked references discuss homosexualityltransgender

Cabo-Raczyska, K., M. Krasinska, and Z. Krasiski (1983) “Behavior and Daily Activity Rhythm of European Bison in Winter.” Acta Theriologica 28:273–99.

*Cabo-Raczyska, K., M. Krasinska, Z. Krasiski, and J. M. Wojcik (1987) “Rhythm of Daily Activity and Behavior of European Bison in the Bialowiea Forest in the Period without Snow Cover.” Acta Theriologica 32:335-72.

*Jaczewski, Z. (1958) “Reproduction of the European Bison, Bison bonasus (L.), in Reserves.” Acta Theriologica 1:333–76.

*Komers, P. E., F. Messier, and C. C. Gates (1994) “Plasticity of Reproductive Behavior in Wood Bison Bulls: When Subadults Are Given a Chance.” Ethology Ecology & Evolution 6:313–30.

*———(1992) “Search or Relax: The Case of Bachelor Wood Bison.” Behavioral Ecology and Sociobiology 31:195–203.

Krasinska, M., and Z. A. Krasiski (1995) “Composition, Group Size, and Spatial Distribution of European Bison Bulls in Bialowieza Forest.” Acta Theriologica 40:1– 21.

*Krasiski, Z., and J. Raczyski (1967) “The Reproduction Biology of European Bison Living in Reserves and in Freedom.” Acta Theriologica 12:407-44.

*Lott, D. F. (1996–7) Personal communication.

*———(1983) “The Buller Syndrome in American Bison Bulls.” Applied Animal Ethology 11:183–86.

———(1981) “Sexual Behavior and Intersexual Strategies in American Bison (Bison bison).” Zeitschrift fur Tierpsychologie 56:115–27.

*———(1974) “Sexual and Aggressive Behavior of Adult Male American Bison (Bison bison).” In V. Geist and E Walther, eds., Behavior in Ungulates and Its Relation to Management, vol. 1, pp. 382–94. Morges, Switzerland: International Union for Conservation of Nature and Natural Resources.

*Lott, D. F., K. Benirschke, J. N. McDonald, C. Stormont, and T. Nett (1993) “Physical and Behavioral Findings in a Pseudohermaphrodite American Bison.” Journal of Wildlife Diseases 29: 360–63.

*McHugh, T. (1972) The Time of the Buffalo. New York: Knopf.

*———(1958) “Social Behavior of the American Buffalo (Bison bison bison).” Zoologica 43:1–40.

*Mloszewski, M. J. (1983) The Behavior and Ecology of the African Buffalo. Cambridge: Cambridge University Press.

*Reinhardt, V. (1987) “The Social Behavior of North American Bison.” International Zoo News 203:3–8.

*———(1985) “Social Behavior in a Confined Bison Herd.” Behavior 92:209– 26.

*Roe, F. G. (1970) The North American Buffalo: A Critical Study of the Species in Its Wild State. Toronto: University of Toronto Press.