Bruce Bagemihl - Biological Exuberance

Younger male Black Bears (adolescents and cubs) sometimes mount their siblings, both male and female. One male approaches another with his ears in a CRESCENT configuration (facing forward and perpendicular from the head), then rears up on his hind legs in a STANDING OVER position, in which he places his front paws on the other male’s back. This develops into sexual mounting as he clasps his partner and gently bites the loose skin on his shoulder, sometimes making pelvic thrusts. The other male often rolls over and begins play-fighting with the mounting male, pawing and biting at him.

Intersexual or hermaphrodite Black and Grizzly Bears occur in some populations. These individuals are genetically female and have female internal reproductive organs, combined with various degrees of external male genitalia. In some cases, they have a penislike organ (complete with a penis bone or BACULUM) that is not connected to the internal reproductive organs, while in others the penis is more fully developed, serving as both a genital orifice connected to the womb as well as a urinary organ. Most transgendered Bears are mothers, mating with males and bearing offspring. Some individuals actually copulate and give birth through their “penis”: their male partner inserts his organ into the tip of the intersexual Bear’s phallus, and the resulting offspring emerge through the penis as well.

Frequency: Female bonding and coparenting among Grizzly Bears occur sporadically. In a 12-year study of one population, for example, bonds between females were observed during 4 of those years (a third of the study period), with roughly 20 percent of all females participating in same-sex bonding and coparenting at some point in their life (usually 1–2 years out of an adult life span of 7–12 years). About 9 percent of all Grizzly cubs are raised in families headed by two (or more) pair-bonded mothers (constituting about 4 percent of all families). Sexual activity between younger male Black Bears occurs only occasionally, comprising perhaps less than 2 percent of their play. The incidence of intersexual Bears is probably sporadic as well, although some populations appear to have fairly high proportions: in Alberta, for example, researchers found that 4 out of 38 Black Bears (11 percent) and 1 of 4 Grizzlies were transgendered.

Orientation: Extended heterosexual pair-bonding and parenting by male-female couples do not occur among Grizzly Bears; however, only a subset of females bond with each other and coparent their young. Thus, some individuals are probably more inclined to form same-sex attachments than others, and these females may even develop same-sex bonds on more than one occasion. Although such females mate with males (and may not bond with females in other years), their primary social relationship during the time they are bonded is with their female companion (and their young). Male Black Bears participate in homosexual mounting only as youngsters and adolescents; most probably go on to mate heterosexually as adults.

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.

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

*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.