Biological Exuberance: Animal Homosexuality and Natural Diversity

the year in the latter species). Among females, approximately 2 percent of Elephant Seal adoptive families involve two pupless females coparenting orphaned pups, and another 14 percent involve one female sharing the care of a pup with its mother. Overall, these two-mother families probably represent about 2–3 percent of all families (the remainder are single-mother).

Orientation: Male Gray Seals exhibit seasonal bisexuality: during the molting period, many bulls participate in preferential homosexual activity—generally ignoring any females present in the herd—while during the mating season heterosexual behavior is the norm. However, only about a third of older males actually copulate with females, while less than 2 percent of younger males (up to eight years old) regularly have access to females. Thus, many bulls probably engage exclusively in homosexual activity for at least part of their lives. Younger adolescent male Elephant Seals—who make up 25–55 percent of the male population— may participate primarily in homosexual mounting, since few actually mate with females. At the other extreme, the highest-ranking bulls are probably exclusively heterosexual, since their attentions are usually directed toward mating (often with hundreds of females each season). Some older adolescent males (40–55 percent of the population) or younger adults may be bisexual, mounting both males and females. However, since less than 9 percent of all males ever mate with females during their lifetime, and less than half of those males surviving to breeding age ever mate, a large number may participate only in same-sex activity (as in Gray Seals). Bulls who mount pups—only a fraction of the male population—do so with equal frequency on both male and female pups. In Harbor Seals, males participate in pair-rolling activity with one another even in the presence of receptive females and generally do so for several months each year (heterosexual mating is usually restricted to a shorter period, perhaps a month or so). Similar patterns of sexual orientation among different age classes probably occur in this species as in the other two.

Nonreproductive and Alternative Heterosexualities

Gray, Harbor, and Northern Elephant Seals engage in a wide variety of nonprocreative heterosexual behaviors. Sexual activity during pregnancy is not uncommon. When female Gray Seals come ashore just before their pups are born, for example, they often participate in heterosexual copulation and other sexual interactions with males, including REVERSE mountings (in which they mount the male rather than vice versa). Male Northern Elephant Seals also mate with pregnant females, including cows who are leaving the breeding grounds after having already been inseminated. Gray and Harbor Seals sometimes copulate outside of the mating season when fertilization is impossible—not only because the females are pregnant, but because (in Grays) males have their own sexual cycle that renders their testes inactive at that time. Heterosexual matings also occasionally occur between these two species. In addition, females in all three species may copulate with multiple male partners.

As noted above, some male Northern Elephant Seals try to copulate with weaned pups—about half of all pups are subjected to such forced mating or rape attempts, which they usually violently resist. In some cases the pups are severely injured by the bulls, with deep gashes and punctures from neck bites. Aggressive sexual behavior by bulls is the leading cause of mortality among pups on the breeding grounds, accounting for the deaths of about 1 in 200 pups each year. Male Northern Elephant Seals also sometimes aggressively mount pups of other species such as Harbor Seals. Similar aggression, violence, and attempted rape—sometimes lethal—is also directed by bulls toward adult females and adolescents. During mating, male Northern Elephant Seals routinely bite, pin down, and slam the full weight of their bodies against females (bulls are 5–11 times heavier than females). A female may be pursued by groups of males as she leaves the rookery, sometimes being raped three to seven times as she tries to escape. Some bulls even try to mate with dead females that have been killed during such attacks (and even with dead seals of other species). Mating in Harbor Seals may also involve aggressive attacks by males, female refusal, and even “gangs” of two or three males forcibly copulating with a female. In addition, Gray and Harbor Seal pups are sometimes killed by adults (accounting for about 7 percent of Gray Seal pup deaths), while roughly 6 percent of Harbor Seal pups are abandoned by their mothers shortly after birth.

For much of the year, the two sexes lead largely segregated lives: Northern Elephant Seal males and females, for example, each embark on their own epic migratory journeys twice a year. Males travel farther north to Alaska while females journey out into the central Pacific, remaining separate for up to 300 days as they traverse more than 13,000 miles in their double migrations. Male Gray Seals are at sea (or molting on land) essentially separate from females for nine to ten months of the year. This segregation is facilitated in part by the phenomenon of DELAYED IMPLANTATION, in which a female’s fertilized embryo remains in “suspended animation” for three to four months, extending the duration of the pregnancy to eleven or more months. Even during the breeding season, many males do not copulate or reproduce: usually only 14–35 percent of the males present on the breeding grounds mate each season. Likewise, more than 90 percent of male Elephant Seals never copulate during their entire lives (most delay breeding until fairly late and simply perish before reaching the age when reproduction usually begins). Because a small number of individuals often monopolize mating opportunities, some populations may experience high levels of inbreeding. In addition, about 20 percent of females skip breeding each year in some populations.

Separation of the sexes continues through pup-rearing: like most polygamous animals, male Seals do not participate in any parenting duties. Females, however, engage in an assortment of fostering activities, often after they have lost their own pup (although some take care of other pups in addition to their own). More than half of all Northern Elephant Seal pups become separated from their mothers each season, and about 18 percent of all females adopt pups. Besides the female coparenting arrangements mentioned above, many females adopt orphan pups on their own, some female Elephant Seals nurse several orphans at once, while others nurse already weaned pups (who become bloated from the extra milk, turning into gigantic “superweaners,” as they are called). Some females even try to “kidnap” or steal pups away from their own mothers, and females who have not lost their own pup often threaten, attack, and even kill stray pups. As many as a quarter to three-quarters of female Gray Seals and 10 percent of female Harbor Seals participate in foster-parenting in some populations.

Other Species

Pairs of female Spotted or Larga Seals (Phoca largha) occasionally coparent their pups together, even sharing in nursing their offspring. Male Sea Otters (Enhydra lutris) have been observed clasping and mounting other males (in the water) in the position usually seen during heterosexual matings. Male Sea Otters also sometimes mount and attempt to mate with Seals, including Harbor Seals and Northern Elephant Seals, and some of these interactions may be same-sex.

Sources

*asterisked references discuss homosexuality/transgender

Allen, S. G. (1985) “Mating Behavior in the Harbor Seal.” Marine Mammal Science 1:84–87.

Amos, B., S. Twiss, P. Pomeroy, and S. Anderson (1995) “Evidence for Mate Fidelity in the Gray Seal.” Science 268:1897–99.

Anderson, S. S. (1991) “Gray Seal, Halichoerus grypus.” In G. B. Corbet and S. Harris, eds., The Handbook of British Mammals, pp. 471–80. Oxford: Blackwell Scientific Publications.

Anderson, S. S., and M. A. Fedak (1985) “Gray Seal Males: Energetic and Behavioral Links Between Size and Sexual Success.” Animal Behavior 33:829–38.

*Backhouse, K. M. (1960) “The Gray Seal (Halichoerus grypus) Outside the Breeding Season: A Preliminary Report.” Mammalia 24:307–12.

———(1954) “The Gray Seal.” University of Durham Medical Gazette 48:9–16.

*Backhouse, K. M., and H. R. Hewer (1957) “Behavior of the Gray Seal (Halichoerus grypus Fab.) in the Spring.” Proceedings of the Zoological Society of London 129:450.

Baker, J. R. (1984) “Mortality and Morbidity in Gray Seal Pups (Halichoerus grypus).” Journal of Zoology, London 203:23–48.

Bishop, R. H. (1967) “Reproduction, Age Determination, and Behavior of the Harbor Seal, Phoca vitulina L. in the Gulf of Alaska.” Master’s thesis, University of Alaska.

Boness, D. J., D. Bowen, S. J. Iverson, and O. T. Oftedal (1992) “Influence of Storms and Maternal Size on