Добавил:
Upload Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
биологическое изобилие.doc
Скачиваний:
0
Добавлен:
01.07.2025
Размер:
2.41 Mб
Скачать

Identification: a medium-sized gazelle; males have distinctive spiral horns and a black-and-white coat; females and juvenile males are tan colored.

THOMSON’S, GRANT’S GAZELLES

IDENTIFICATION: Smaller gazelles (2—3 feet at shoulder height) with ringed, slightly S-shaped horns in both sexes; Thomson’s have a conspicuous black flank band, and Grant’s horns may bend sharply outward. DI.

Social Organization

Blackbucks live in small, same-sex herds containing 10–50 individuals. Female herds circulate within the territory of one or several adult males who mate with them; the remaining males live in “bachelor” herds on the periphery of the breeding territories. Thomson’s and Grant’s Gazelles have a similar social organization, except that mixed herds containing both males and females also form, especially during migration.

Description

Behavioral Expression: The majority of male Blackbucks have homosexual interactions: among all age groups, mounting of one male by another occurs in the position used for heterosexual intercourse. Usually mounting happens during play-fighting—friendly sparring matches with erotic overtones, sometimes involving three males at a time. In addition, adult males often perform courtship displays toward adolescent males (one-to-two-year-olds) prior to mounting them. These displays, which also occur in heterosexual interactions, begin with the older male DISPLAY WALKING: he stands some distance away from the object of his attentions, lowering his ears and curling his tail up to touch his back. He walks in this posture parallel to the younger male so that the younger one has to walk in a circle. This is followed by PRESENTING THE THROAT: the older male raises his nose high in the air so that his spiral horns touch the back of his neck. This exposes the striking black-and-white pattern of his neck. While doing this, he briskly kicks first one foreleg, then the other, in front of him several times in a row, sometimes reaching under the other male’s belly or between his thighs. Occasionally, the older male makes a distinctive barking sound as he does this. This is then followed by mounting of the younger male by the older. Occasionally, female Blackbucks mount other females.

A male Blackbuck mounting another male during a bout of play-fighting

In Thomson’s Gazelles, male homosexual mounting may occur in a variety of contexts, including during migration and in encounters between two nonterritorial males. Males also occasionally direct courtship displays toward one another, including the NECK-STRETCH, FORELEG KICK, and NOSE-UP POSTURE, as well as the PURSUIT MARCH (the latter similar to heterosexual courtships). Homosexual courtship displays are preceded by one or both males displaying their horns to the other (often interpreted as a threatening gesture). Homosexual mounting in Grant’s Gazelles typically occurs as part of a formalized display in which two males march toward one another, lifting their heads high and showing their white throat patches when they are next to each other. The mounted male, if an adult, often attacks the male trying to mount him (females also sometimes respond aggressively to a male’s advances, see below).

Frequency: Male homosexual activity is common among Blackbucks: at any given time, fully three-quarters of the male population lives in the bachelor herds, where most homosexual interactions take place. Among Thomson’s and Grant’s Gazelles, homosexual behavior is much less frequent: 12 percent of encounters between male Grant’s involve mounting, while 1–8 percent of encounters between male Thomson’s involve sexual behavior.

Orientation: All Blackbuck males over three years old leave the bachelor herd temporarily to attempt mating with females. However, this usually occurs only once or twice in each male’s lifetime; for the remainder of his life, he interacts homosexually. Technically, then, all male Blackbuck are bisexual, though in practice they are predominantly homosexual. In Thomson’s Gazelles, homosexual mounting typically occurs among males in bachelor or migratory groups, not territorial males (who are involved principally in heterosexual activities). Although these males occasionally court and attempt to mount females, the majority of their sexual interactions may be with other males. In Grant’s males, homosexual behavior does occur in some territorial males; since these males direct sexual behaviors toward both males and females, they are functionally bisexual (although males generally do not consent to being mounted by other males).

Nonreproductive and Alternative Heterosexualities

Because of the organization of Blackbuck society into sex-segregated herds and the small number of active breeding males, only a fraction of the male population is ever involved in heterosexual activity. Furthermore, although all males attempt to leave the bachelor herds and mate with females, most are unable to do so because of the males already defending the breeding territories; consequently life in the bachelor herd is preferable for many males. Among Grant’s and Thomson’s Gazelles, there are similar patterns of sex segregation and nonparticipation in heterosexuality—in fact, more than 90 percent of the male Grant’s population may be composed of nonbreeders at any given time. In addition, female Grant’s Gazelles often behave aggressively toward males during heterosexual courtship, performing threat displays and sometimes even fighting bucks to fend off unwanted advances. Female Blackbucks sometimes engage in nonreproductive mounts of fawns or young animals.

WILD SHEEP, GOATS, AND BUFFALO

BIGHORN SHEEP