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Mammals - Lowland Gorilla

Region: Africa

Class: Mammalia

Order: Primata

Family: Hominidae

Genus: Gorilla

Scientific Name: Gorilla gorilla gorilla

Description: Gorillas are the largest of the primates, the Mountain Gorilla (Gorilla beringie) being only slightly larger than the Lowland Gorilla and with thicker and longer hair. Weight ranges from 85 to 175 kg with males being twice as heavy as females. Weights of 290 kg. for a male and 100 kg. for a female are on record. Captive gorillas tend to weigh more. The male is very stocky and powerful in the body, with wide shoulders and chest. The females are much smaller and lighter.

Distribution: Congo River basin of Western Africa.

Habitat: Lowland rain forest.

Food: Mainly juicy plant stems, vines and leaves. Bark, roots and fruits are also taken, the choice parts being selected, the remainder discarded. There is a definite preference shown in plant selection, wild celery, thistles, nettles, bamboo shoots and bedstraw (Galluim) are among those chosen.

Skin/Color/Coat: The colour of the coat varies considerably, ranging through black, silver and shades of red. Black is more usual. The skin is also black. As a male gorilla reaches physical maturity (between 12 and 15 years of age), he develops his silvery grey colouration. Old males often lack chest hair. The face, ears, palms and soles of feet are bare.

Vocalization: The gorillas vocalize a great deal from the throat. Roars, growls, barks, grunts, purrs, croaks, hoots, squeaks and screeches are among those used. They can very effectively warn each other of impending danger and intimidate intruders. The hooting sound is usually the prelude to the climax to their emotional expression - the drumming display. Flat or slightly cupped hands are beat in rapid alternation upon the chest, abdomen, hips, tree trunks, on the ground, or on anything that is handy. Drumming sounds the alarm in case of danger, threatens the invader, but it may also be done in play.

Reproduction and Development: Females mature sexually at 6-8 years, with the onset of menstruation and are fully grown at 8-10 years of age. The males are sexually mature at 8-10 years and fully grown at 12-15 years. In male apes as in man, potency, once achieved, is continuous until it is lost through disease or senescence. Female gorillas have a menstrual cycle similar to that in humans, the average length being 30-31 days. In the wild, copulation is normally dorso-ventral, in captivity both dorso-ventral and ventro-ventral copulations occur. The average gestation period is 265 days. A single young is born weighing approximately 2 kg. The baby gorilla is completely dependent on its mother for food and protection. At birth they appear to lack the strength to grasp their mother's hair, so she will support her infant with both hands. When on the move, she cradles the infant to her breast with one hand. The infant stays with the mother for the first three years of its life. It begins to eat vegetable matter at about 6 weeks of age, but nursing continues for another year and a half to two years. By one month, the infant clings to its mother unaided; by three months it rides on its mother's back; by four or five months it can walk unaided, by six months it can climb as well and it is most active. Young gorillas are very playful. Juveniles climb more frequently and with greater ease than the adults. Very often other females will play the role of "aunt" to a baby and participate in its care, playing with it and carrying it around. Gorillas live in fairly stable groups of 5 to 15 individuals. Larger bands consist of an adult male, several younger males and a large number of females with their young. Smaller groups may consist of only one adult male with a few females and their young. The oldest gorilla in captivity was "Massa" who died at the age of 54 in the Philadelphia Zoo.

Adaptations: Gorillas are strictly diurnal in habit, building nests to rest in each night. Day nests are built as well. Both types of nests may be built on the ground or in trees. When they build in trees, they are seldom more than 9 metres from the ground. The adult male because of his size does not build nests in trees. Nests are occupied for one night only. Gorillas collect their varied foods mainly on the ground. Gorillas are quiet most of the time, they enjoy dozing and sunbathing in the mid-morning between bouts of feeding. Postures, gestures, facial expressions and vocalizations are all used in communication within the group. Only one or two sounds carry far enough to reach other groups; one of them is the chest beating sound and also the sound heard during the intimidating display that gorillas frequently give among themselves or to an intruder. This display includes rising on its legs, throwing vegetation in their, leg kicking, running sideways, slapping and tearing nearby vegetation, and thumping the ground. Many variations occur, and some acts may occur alone. Aggressive charges rarely result in serious physical combat, the gorilla avoids conflict until extremely hard pressed; the dominant male always acting in defense of his group.

Threats: The gorilla's chief enemy is man. Gorillas are widely hunted for "bush meat" and the young are collected for sale, a practice that is now illegal. The leopard is also a threat.

Status: Endangered. The population has been severely reduced due to wars, logging and the

References: (1)Baillie, J. & B. Goombridge, 1996 IUCN Red List of Threatened Animals, IUCN, Gland, Switzerland, 1997, Pp. 368. (2)Nowak, Ronald, M., Walker’s Mammals of the World, Fifth Edition, Vol. 1, 1991, Pp. 503-06.