Biological Exuberance: Animal Homosexuality and Natural Diversity

Nonreproductive and Alternative Heterosexualities

Some Grizzly and Black Bear populations have significant numbers of nonbreeding animals. Each year, perhaps as many as one-third to one-half of all female Grizzlies do not mate or are otherwise nonreproductive (including copulating with males without becoming pregnant), and some individuals do not breed during their whole lives. In some Black Bear populations, only 16–50 percent of the adult females reproduce each year, and many skip breeding for several years. Female Bears who do become pregnant exhibit DELAYED IMPLANTATION—the fertilized embryo ceases development for about five months before implanting in the uterus. In some cases embryos are reabsorbed, aborted, or prevented from implanting rather than carried to term (e.g., when food supplies are inadequate). In addition, many female Grizzlies and Black Bears delay reproducing anywhere from one to four years after they become sexually mature. Juvenile (sexually immature) Black and Grizzly Bears also engage in sexual activity with each other, including mounting and licking of the vulva. Among adult male Grizzly Bears, higher-ranking individuals often have lower copulation rates because of their preoccupation with aggressive interactions, and in some populations top-ranked males may actually go entire breeding seasons without mating at all. When mating does take place, one partner may display indifference or refusal, and as many as 47 percent of all copulations are incomplete in that they do not involve full penetration or ejaculation. Occasionally, a particularly aggressive male will force a female to mate with him, although females usually have control of the interaction. In fact, females often mate with multiple partners—as many as eight males in a single breeding season for Grizzlies, four to six for Black Bears—and cubs belonging to the same litter may be fathered by different males. Nevertheless, male Black and Grizzly Bears can become violent toward females and cubs, occasionally even killing and cannibalizing adults and/or young. Female Black Bears also sometimes kill cubs that are not their own (especially during the nursing period), although it is not uncommon for mothers of both species to adopt cubs that have been orphaned or abandoned.

Other Species

Intersexual or transgendered individuals also occur among Polar Bears (Ursus maritimus), comprising about 2 percent of some populations.

Sources

*asterisked references discuss homosexuality/transgender

Alt, G. L. (1984) “Cub Adoption in the Black Bear.” Journal of Mammalogy 65:511- 12.

Brown, G. (1993) The Great Bear Almanac. New York: Lyons and Beuford.

*Cattet, M. (1988) “Abnormal Sexual Differentiation in Black Bears (Ursus americanus) and Brown Bears (Ursus arctos).” Journal of Mammalogy 69:849–52.

*Craighead, F. C., Jr. (1979) Track of the Grizzly. San Francisco: Sierra Club Books. *Craighead, F. C., Jr., and J. J. Craighead (1972) “Grizzly Bear Prehibernation and Denning Activities as Determined by Radiotracking.” Wildlife Monographs 32:1–35

*Craighead, J. J., J. S. Sumner, and J. A. Mitchell (1995) The Grizzly Bears of Yellowstone: Their Ecology in the Yellowstone Ecosystem, 1959–1992. Washington, D.C. and Covelo, Calif.: Island Press.

*Craighead, J. J., M. G. Hornocker, and F. C. Craighead Jr. (1969) “Reproductive Biology of Young Female Grizzly Bears.” Journal of Reproduction and Fertility, suppl. 6:447–75.

Egbert, A. L. (1978) “The Social Behavior of Brown Bears at McNeil River, Alaska.” Ph.D. thesis, Utah State University.

Egbert, A. L., and A. W. Stokes (1976) “The Social Behavior of Brown Bears on an Alaskan Salmon Stream.” In M. R. Pelton, J. W. Lentfer, and G. E. Folk, eds., Bears—Their Biology and Management: Papers from the Third International Conference on Bear Research and Management, pp. 41–56. Morges, Switzerland: International Union for Conservation of Nature and Natural Resources.

Erickson, A. W., and L. H. Miller (1963) “Cub Adoption in the Brown Bear.” Journal of Mammalogy 44:584–85.

Goodrich, J. M., and S. J. Stiver (1989) “Co-occupancy of a Den by a Pair of Great Basin Black Bears.” Great Basin Naturalist 4:390–91.

*Henry, J. D., and S. M. Herrero (1974) “Social Play in the American Black Bear: Its Similarity to Canid Social Play and an Examination of Its Identifying Characteristics.” American Zoologist 14:371– 89.

Jonkel, C. J., and I. McT. Cowan (1971) “The Black Bear in the Spruce-Fir Forest.” Wildlife Monographs 27:1–57.

Rogers, L. (1976) “Effects of Mast and Berry Crop Failures on Survival, Growth, and Reproductive Success of Black Bears.” Transactions of the North American Wildlife and Natural Resources Conference 41:431–38.

Schenk, A., and K. M. Kovacs (1995) “Multiple Mating Between Black Bears Revealed by DNA Fingerprinting.” Animal Behavior 50:1483–90.

Stonorov, D., and A. W. Stokes (1972) “Social Behavior of the Alaska Brown Bear.” In S. Herrero, ed., Bears —Their Biology and Management: Papers from the Second International Conference on Bear Research and Management, pp. 232-42. Morges, Switzerland: International Union for Conservation of Nature and Natural Resources.

Tait, D. E. N. (1980) “Abandonment as a Reproductive Tactic—the Example of Grizzly Bears.” American Naturalist 115:800–808.

Wimsatt, W. A. (1969) “Delayed Implantation in the Ursidae, with Particular Reference to the Black Bear (Ursus americanus Pallus).” In A. C. Enders, ed., Delayed Implantation, pp. 49–76. Chicago: University of Chicago Press.

IDENTIFICATION: A yellowish brown hyena with spotted flanks and back, a strongly sloping body profile, and rounded ears; females typically heavier than males. DISTRIBUTION: Sub-Saharan Africa. HABITAT: Open country, including plains, semidesert, savanna. STUDY AREAS: Kalahari and Gemsbok National Parks, South Africa and Botswana; University of California–Berkeley.

Social Organization

Spotted Hyenas live in matrilineal clans of 30–80 individuals. Females are dominant to males and remain in their home group for life, while males emigrate to single-sex groups during adolescence and then join other clans (usually for only a few years at a time) on reaching adulthood. This species has a highly organized social system, engaging in cooperative hunting and communal denning. The breeding system is polygynous: generally only one male in each clan mates with several females. Spotted Hyenas are largely nocturnal.

Description

Behavioral Expression: Female Spotted Hyenas have an extraordinary genital configuration that makes them superficially resemble males: the clitoris is 90 percent of the length of the male’s penis (nearly seven inches long) and equal to it in diameter; it can be fully erected. In addition, the labia are fused to resemble a “scrotum” containing fat and connective tissue that give the appearance of testes. There is no vaginal opening—instead, the female mates and gives birth (as well as urinates) through the tip of her clitoris. Heterosexual mating is accomplished by retracting the clitoris inside the abdomen, essentially turning it inside out to form a passageway within which the male can insert his penis. Homosexual mounting between females also occurs in this species; in some cases, an adolescent or younger adult mounts an older one. During a homosexual encounter, one female approaches another with her clitoris erect, often “flipping” it up against her abdomen as a sign of sexual arousal (also seen in males preparing to mate). She may lick her partner on the back, then mount by rising up and clasping her front paws around the other female, resting her head on the other’s neck, and thrusting against her. Clitoral penetration may also occur, though it is not common. Sometimes the female being mounted appears to be disinterested or nonchalant and may even wander off during mounting. These are also characteristics of heterosexual courtship and copulation—females often walk away or do not permit males to achieve penetration and, indeed, may be overtly aggressive toward them. Spotted Hyenas also perform a MEETING