Biological Exuberance: Animal Homosexuality and Natural Diversity

incomplete mounts by males. Males also frequently mount females during nonfertile periods, including pregnancy. Male Warthogs have been observed spontaneously ejaculating, including in their sleep. In addition, opposite-sex mountings in both species sometimes consist of a male mounting the female from the side without actual penetration (about 2 percent of sexual behavior in Collared Peccaries). Moreover, insemination does not necessarily occur even if penetration does, due to VAGINAL PLUGS. In both Collared Peccaries and Warthogs, a gelatinous barrier in the female’s reproductive tract is deposited by a male when he copulates, very likely insuring that sperm from any subsequent matings cannot impregnate the female. Since female Warthogs usually copulate with more than one male, and female Collared Peccaries often mate repeatedly with the same male (as many as 18 times in three hours), a large proportion of copulations are therefore probably nonprocreative. Females can also refuse copulations by covering the vulva with their tail and tightening their leg muscles upward. In Collared Peccaries, offspring are cared for not only by their biological mothers, but also by “nursemaids,” usually older sisters of the youngsters, that defend and nurse them. Often the nursemaids are not in fact sexually mature—they may be as young as six months old—with the amazing consequence that many nursemaids are themselves still nursing from their own “nursemaids.” It is thought that they are able to produce milk because they consume the mother’s placenta when she gives birth, perhaps thereby receiving some sort of hormonal influence from the mother. In Warthogs a number of violent counterrepro-ductive activities also occur: adult males occasionally kill their younger brothers or cannibalize other males that they kill.

Other Species

Same-sex mounting also occurs in White-lipped Peccaries (Tayassu pecari) among both males and females.

Sources

asterisked references discuss homosexuality/transgender

Bissonette, J. A. (1982) Ecology and Social Behavior of the Collared Peccary in Big Bend National Park, Texas. Scientific Monograph Series no. 16. Washington, D.C.: U.S. National Park Service.

Byers, J. A., and M. Bekoff (1981) “Social, Spacing, and Cooperative Behavior of the Collared Peccary, Tayassu tajacu.” Journal of Mammalogy 62:767–85.

Child, G., H. H. Roth, and M. Kerr (1968) “Reproduction and Recruitment Patterns in Warthog (Phacochoerus aethiopicus) Populations.” Mammalia 32:6– 29.

Cumming, D. H. M. (1975) A Field Study of the Ecology and Behavior of Warthog. Salisbury, Rhodesia: Trustees of the National Museums and Monuments of Rhodesia.

*Dubost, G. (1997) “Comportements compares du Pecari a levres blanches, Tayassu pecari, et du Pecari a collier, T. tajacu (Artiodactylea, Tayassuides) [Comparative Behaviors of the White-lipped Peccary and of the Collared Peccary (Artiodactyla, Tayassuidae)].” Mammalia 61:313–43.

Fradrich, H. (1965) “Zur Biologie und Ethologie des Warzenschweines (Phacochoerus aethiopicus Pallas), unter Beriicksichtigung des Verhaltens anderer Suiden [On the Biology and Ethology of Warthogs, in View of the Behavior of Other Suidae].” Zeitschrift fur Tierpsychologie 22:328–93.

Packard, J. M., K. J. Babbitt, K. M. Franchek, and P. M. Pierce (1991) “Sexual Competition in Captive Collared Peccaries (Tayassu tajacu).” Applied Animal Behavior Science 29:319–26.

Schmidt, C. R. (1990) “Peccaries.” In Grzimek’s Encyclopedia of Mammals, vol. 5, pp. 48–55. New York: McGraw-Hill.

*Somers, M. J., O. A. E. Rasa, and B. L. Penzhorn (1995) “Group Structure and Social Behavior of Warthogs Phacochoerus aethiopicus.” Acta Theriologica 40:257–81.

*Sowls, L. K. (1997) Javelinas and Other Peccaries: Their Biology, Management, and Use. College Station: Texas A&M University Press.

*———(1984) The Peccaries. Tucson: University of Arizona Press.

*———(1974) “Social Behavior of the Collared Peccary Dicotyles tajacu (L.).” In V. Geist and F. Walther, eds., The Behavior of Ungulates and Its Relation to Management, vol. 1, pp. 144–65. IUCN Publication no. 24. Morges, Switzerland: International Union for Conservation of Nature and Natural Resources.

*———(1966) “Reproduction in the Collared Peccary (Tayassu tajacu).” In I. W. Rowlands, ed., Comparative Biology of Reproduction in Mammals, Symposia of the Zoological Society of London no. 15, pp. 155–72. London and New York: Academic Press.

Torres, B. (1993) “Sexual Behavior of Free-Ranging Amazonian Collared Peccaries (Tayassu tajacu.)” Mammalia 57:610–13.

IDENTIFICATION: A small (3 feet at shoulder), camel-like animal with a slender body and a long, thin neck; coat is tawny brown or sandy-colored with white underparts and a chest mane. DISTRIBUTION: Andes Mountains of Peru, Bolivia, Argentina, Chile. HABITAT: High-elevation grasslands, plains. STUDY AREAS: Aricoma and Huaylarco, Peru.

Social Organization

Vicunas live in cosexual groups usually containing 1 male, 3–10 females, and their offspring. In addition, all- male groups are a regular feature of Vicuna populations; they usually contain 5–10 animals, but may swell to include more than 150 individuals.

Description

Behavioral Expression: Female Vicunas sometimes mount each other, with one animal straddling the other’s back with her forelegs. This is similar to a heterosexual mating, except the mounted animal does not typically lie down as she would if a male were mounting her (even in heterosexual interactions, though, the female does not always cooperate by lying down). In one case, a pregnant female chased another female and mounted her. Adolescent males also sometimes mount one another during play-fighting, remaining astraddle for up to a quarter of a minute. Play-fights are gentle frolics in which the two males push and wrestle each other with their heads and long necks, interspersed with chasing or rearing on the hind legs.

Frequency: Same-sex mounting probably occurs only sporadically in Vicunas. However, heterosexual mating is also infrequent: during a seven-month study period, for example, 5–11 heterosexual matings were observed compared to one mount between females.

Orientation: At least some females that mount other females are bisexual, since this behavior occurs in pregnant females. During the time that adolescent males are living in bachelor groups, the majority of their mounting activities are same-sex. Many of these males will go on to mate heterosexually, although about 10 percent of the nonbreeding animals in male bands are adults.

Nonreproductive and Alternative Heterosexualities

About 40 percent of Vicunas do not breed: many are younger males living in the sex-segregated male groups (although these also include some adults), and there are solitary older animals as well. Among breeding animals, there is often considerable antagonism between the sexes: males have been known to fight with pregnant females, and territorial males are openly hostile toward females from neighboring bands, often chasing and attacking them. During copulation, females sometimes refuse to lie down; a male may try to force his partner to mate by bringing his full weight onto her back, causing the female to stagger underneath him. Adult males occasionally copulate with yearling females, who are probably not old enough to breed. Sexual activity between males and females also takes place outside of the breeding season.

Sources