Bruce Bagemihl - Biological Exuberance

Behavioral Expression: Male American Bison participate in a variety of homosexual activities. Among younger bulls (less than five years old, particularly one-to-three-year-olds), anal intercourse is common. One male mounts the other with an erect penis and achieves anal penetration; the animal being mounted often facilitates the sexual interaction by positioning his hips or backing toward the other male with his tail lifted to the side. Homosexual copulation lasts on average nearly twice as long as heterosexual mating. The same bull may be mounted several times in succession by one or several other males, but reciprocal mounting is less common, since bulls that mount other males often do not allow themselves to be mounted (although males that are mounted do try to mount their partners). Males that are frequently mounted by other males often exhibit tears in the skin on their back where the mounting bull’s hooves rub on either side of their spine. An identical type of skin abrasion is seen in female Bison that are frequently mounted by males. Homosexual mounting also occurs in a number of other contexts: in Bison (both American and European) and African Buffalo, males sometimes mount each other during play-fighting. An adult male American Bison may also mount another bull at the conclusion of an aggressive interaction. In these two contexts, mounting usually does not involve penetration, although erection of the penis and pelvic thrusting may occur. Sometimes one male will rest his chin on the other’s rump as a prelude to mounting, often while making a soft panting sound. Female homosexual mounting and CHIN-RESTING also occur in Wisent and African Buffalo.

American Bison bulls—especially younger males—also sometimes form a TENDING BOND or consortship with 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.

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).

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.

*asterisked references discuss homosexuality/transgender

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

*Caboń-Raczyńska, K., M. Krasinska, Z. Krasiński, and J. M. Wójcik (1987) “Rhythm of Daily Activity and Behavior of European Bison in the Białowieża 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.