Biological Exuberance: Animal Homosexuality and Natural Diversity

*Boyd, L. E. (1991) “The Behavior of Przewalski’s Horses and Its Importance to Their Management.” Applied Animal Behavior Science 29:301–18.

*———(1986) “Behavior Problems of Equids in Zoos.” In S. L. Crowell-Davis and K. A. Houpt, eds., Behavior, pp. 653–64. The Veterinary Clinics of North America: Equine Practice 2(3). Philadelphia: W. B. Saunders.

*Boyd, L. E. and K. A. Houpt (1994) “Activity Patterns.” In L. Boyd and K. A. Houpt, eds., Przewalski’s Horse: The History and Biology of an Endangered Species, pp. 195–227. Albany: State University of New York Press.

Houpt, K. A., and L. Boyd (1994) “Social Behavior.” In L. Boyd and K. A. Houpt, eds. Przewalski’s Horse: The History and Biology of an Endangered Species, pp. 229–54. Albany: State University of New York Press.

Klingel, H. (1990) “Horses.” In Grzimek’s Encyclopedia of Mammals, vol. 4, pp. 557 -94. New York: McGraw-Hill.

———(1969) “Reproduction in the Plains Zebra, Equus burchelli boehmi: Behavior and Ecological Factors.” Journal of Reproduction and Fertility, suppl. 6:339-45.

Lloyd, P. H., and D. A. Harper (1980) “A Case of Adoption and Rejection of Foals in Cape Mountain Zebra, Equus zebra zebra.” South African Journal of Wildlife Research 10:61–62.

Lloyd, P. H., and O. A. E. Rasa (1989) “Status, Reproductive Success, and Fitness in Cape Mountain Zebra (Equus zebra zebra).” Behavioral Ecology and Sociobiology 25:411–20.

*McDonnell, S. M., and J. C. S. Haviland (1995) “Agonistic Ethogram of the Equid Bachelor Band.” Applied Animal Behavior Science 43:147-88.

Monfort, S. L., N. P. Arthur, and D. E. Wildt (1994) “Reproduction in the Przewalski’s Horse.” In L. Boyd and K. A. Houpt, eds., Przewalski’s Horse: The History and Biology of an Endangered Species, pp. 173-93. Albany: State University of New York Press.

*Penzhorn, B. L. (1984) “A Long-term Study of Social Organization and Behavior of Cape Mountain Zebras Equus zebra zebra.” Zeitschrift fur Tierpsychologie 64:97–146.

Rasa, O. A. E., and P. H. Lloyd (1994) “Incest Avoidance and Attainment of Dominance by Females in a Cape Mountain Zebra (Equus zebra zebra) Population.” Behavior 128:169-88.

Ryder, O. A., and R. Massena (1988) “A Case of Male Infanticide in Equus przewalskii.” Applied Animal Behavior Science 21:187–90.

*Schilder, M. B. H. (1988) “Dominance Relationships Between Adult Plains Zebra Stallions in Semi-Captivity.” Behavior 104:300–319.

Schilder, M. B. H., and P. J. Boer (1987) “Ethological Investigations on a Herd of Plains Zebra in a Safari Park: Time-Budgets, Reproduction, and Food Competition.” Applied Animal Behavior Science 18:45–56.

van Dierendonck, M. C., N. Bandi, D. Batdorj, S. Dugerlham, and B. Munkhtsag (1996) “Behavioral Observations of Reintroduced Takhi or Przewalski Horses (Equus ferus przewalskii) in Mongolia.” Applied Animal Behavior Science 50:95–114.

WARTHOG

IDENTIFICATION: A 3—5-foot-long wild pig with a large head, prominent tusks, and distinctive warts in front of the eyes and on the jaw. DISTRIBUTION: Sub-Saharan Africa. HABITAT: Steppe, savanna. STUDY AREA: Andries Vosloo Kudu Reserve, South Africa.

COLLARED PECCARY

IDENTIFICATION: A piglike mammal with grayish, speckled, or salt-and-pepper fur and a light- colored collar. DISTRIBUTION: Arizona, New Mexico, Texas, southward to northern Argentina. HABITAT: Varied, including desert, woodland, rain forest. STUDY AREAS: In the Tucson Mountains and near Tucson, Arizona; University of Arizona; National Institute of Agronomic Research, French Guiana; subspecies T.t. sonoriensis.

Social Organization

Warthogs tend to associate in matriarchal groups (also known as SOUNDERS) of several females and their offspring, and in all-male “bachelor” groups. Only 3 percent of groups contain both males and females, and many Warthog males are solitary. Males join female groups only briefly for mating, which is usually promiscuous—both males and females copulate with multiple partners—and the only long-lasting bonds that form are between animals of the same sex, primarily females. Collared Peccaries live in herds of 5–15 individuals, containing animals of both sexes.

Description

Behavioral Expression: Homosexual mounting occurs in both Collared Peccaries and Warthogs. In Collared Peccaries, females in heat often RIDE or mount other females, and males occasionally mount one another as well. In Warthogs, homosexual mounting also takes place among females in heat, though it is less common. Sometimes a female Warthog will mount another female from the side, a position that is also occasionally used in heterosexual mounting. Warthog females often develop long-lasting bonds with each other, and same-sex mounting can be a part of these pairings (stable male-female pairs do not occur in this species). The two females associate together for many years and may even jointly raise their young, combining their litters and suckling each other’s offspring. In addition, when one female is injured or temporarily unable to look after her young, the other female will take over parental duties. One such pair was seen consistently chasing away males who tried to get close to them. Biologists studying Warthogs call these pairs or groups of adult females without any males or offspring SPINSTER groups—they typically contain an older female with a younger one. Some of these pairings involve related females, such as sisters or mother and daughter—in which case some same-sex mounting may be incestuous—although nonrelated pairings also occur. Occasionally two male Warthogs pair off as well, though no sexual behavior has been observed between them.

female Collared Peccary “riding” another female

Frequency: Homosexual mounting occurs commonly in Collared Peccaries during heat; it is less frequent in Warthogs, probably comprising 1–3 percent of all mountings. About 5 percent of all Warthog groups are “spinster” (female-only) groups.

Orientation: Females that participate in same-sex mounting are probably bisexual, since most also engage in heterosexual relations. Warthog female companions, for example, may mate with males and reproduce, even if they do not consistently socialize with males. More than a quarter of Warthog females do not get pregnant each season, however, so it is possible that some are involved exclusively in same-sex (bonding and/or sexual) activities.

Nonreproductive and Alternative Heterosexualities

Significant portions of Warthog populations do not procreate. In addition to the nonbreeding females and sex-segregated groups mentioned above, one- and two-year-olds that are sexually mature may remain with their mother’s group to help raise additional litters (rather than breeding themselves). These two species also participate in a variety of nonreproductive sexual behaviors. About 6 percent of heterosexual activity in Collared Peccaries, for example, involves females mounting males (REVERSE mounts), while another 22 percent of copulations are