GORILLA

Male gorilla (Gorilla gorilla). largest of the anthropoid, or manlike, apes (family Pongidae). It is the closest living relative to humans with the exception of the chimpanzee. The gorilla is a forest dweller native to equatorial Africa. Most authorities separate the single species, Gorilla gorilla, into three races: the western lowland gorilla (G. g. gorilla), found in the lowland tropical rainforests from Cameroon to the Congo River; the eastern lowland gorilla (G. g. graveri), found in the lowland tropical rainforests of the eastern Congo region; and the mountain gorilla (G. g. beringei), found in the Lake Kivu region, including montane rainforests and bamboo forests of the mountainous terrain to the north and east. The gorilla is a stocky, powerful ape with black skin and hair, large nostrils, and prominent brow ridges. It is larger than its closest relative, the chimpanzee, but has smaller ears and a less boisterous disposition. The adult gorilla has long, powerfully built arms and short, stocky legs. It has an extremely thick, strong chest and a protruding abdomen. The adult male gorilla has a prominent crest on top of the skull and a "saddle" of gray or silver hairs on the lower part of the back (hence the name silverback for mature males). The male is about twice as heavy as the female and may attain a height of about 1.7 m (5.5 feet) and a weight (in the wild) of 135-275 kg (300-600 pounds). Captive gorillas of both sexes may grow quite fat and hence become much heavier. An adult wild female typically has a height of about 1.5 m (5 feet) and weighs about 90 kg (200 pounds). The gorilla lacks hair on its face, hands, and feet, and the chest of old males is bare. The hair of the mountain gorilla is longer than that of the other two subspecies. Much has been written about the ferocity of the gorilla, but studies indicate that it is an unaggressive, even shy, animal unless unduly disturbed. Intruders may be faced by the male leader of a group, who may make aggressive displays in attempting to protect his dependents; commonly these involve chest-beating, vocalization, or short rushes toward the intruder, followed in most instances by a discreet withdrawal. Gorillas live in stable family groups of from 6 to 20 animals that are led by one or two silverbacked males. The other members in a group are females, infants, juveniles, and young adult males (blackbacks). The gorilla is diurnal and primarily terrestrial, usually walking about on all four limbs, with part of its weight supported on the knuckles of its hands. Very occasionally it stands erect. Females and young climb more than males. The diet is vegetarian and includes such foods as leaves, stalks, and shoots. Much of the day is spent foraging and resting, with a group traveling a few hundred yards in between several feeding bouts taken each day. At dusk, each gorilla builds a crude sleeping nest by bending branches and foliage. A new nest is built each night and is constructed either on the ground or in the trees. Each group wanders through a territory with a total area of about 25-40 square km (10-16 square miles), though several different groups may share the same part of the forest. Although the gorilla is a relatively quiet animal, it has a variety of calls including grunts, hoots, and the roar given by an aggressive male. The well-known chest-beating of the gorilla is performed by both males and females. When performed by males, it is part of a ritual that may also include such acts as running about, tearing at vegetation, and slapping the ground. The exact purpose of this display is unknown, but at times it appears to be used to intimidate outsiders (gorilla or human). At other times, it seems to be used to maintain the dominance hierarchy within the group. Although they lack the curiosity and adaptability of chimpanzees, gorillas are calmer and more persistent. Captive gorillas have shown a capacity for problem solving and have demonstrated that they possess a degree of insight as well as memory and anticipation of experience. They appear to be more adept than chimpanzees at learning sign language from humans. A wild female gorilla gives birth about once every four years and has no fixed breeding season. The gestation period is about 250-290 days, and births are usually single, though twins do occur rarely. A newborn gorilla weighs only about 2 kg (4.5 pounds) and is utterly helpless for the first three months of life, during which it is carried in its mother's arms. The young gorilla sleeps in its mother's nest at night and rides on her back during the day. Female gorillas reach reproductive maturity at about 7 years of age, males at about age 9. The life expectancy of a wild gorilla is about 30 years, while captive gorillas have lived into their 40s. The gorilla has become increasingly rare throughout its range, having suffered from human destruction of its forest homelands and, in the past, from big-game hunting and from over-collection by zoos and research institutes. The entire species is listed as vulnerable in the Red Data Book, and the mountain gorilla is classified as endangered, having an estimated population of only 500 to 1,000 individuals. Reasons for the near extinction of this race include continued loss of habitat as a result of human activities (farming, grazing, and lumbering) and illegal hunting to satisfy a flourishing black market for gorilla "trophies" (especially heads, hands, and skins).