Gorillas are the largest of the apes, the males reaching a height of 5 to 6 ft (150–190 cm) with a 9-ft (144–cm) arm spread. Males weigh about 450 lb (200 kg) in the wild; in zoos they become obese and may reach 600 lb (270 kg) or more. Male gorillas have prominent sagittal crests and brow ridges and large canine teeth; these features are less developed in females. Females are smaller than males, weigh about half as much, and do not develop the gray hair on the back characteristic of the sexually mature male. Females bear one infant about every four years; the child is carried in the mother's arms and then on her back. Females mature in 8 or 9 years, males in 11 or 12; gorillas may live more than 40 years.
Dominant older males, called silverbacks, usually lead stable harem societies of 2 to 30 females and juvenile males in a daily search for food. The animals normally walk on all fours, resting their upper body on their knuckles. They are vegetarians, living on a variety of vines, leaves, fruit, roots, and bark. Mountain gorillas eat wild celery, bamboo shoots, nettles, thistles, and sometimes certain soils or a rare form of fungus. Adolescents and small females may climb trees in search of food and to build arboreal nests for sleeping. Adults of both sexes build ground nests daily.
Quiet and retiring in temperament when compared to the excitable chimpanzee, gorillas have been known to attack humans in defense of their family group. Gorillas normally rely on bluffs, roaring and beating their chests to frighten intruders. Their main enemies are human poachers; in the lowlands, leopards may sometimes eat the young. Disease and deforestation are also serious threats.
Gorillas are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Primates, family Hominidae.
See D. Fossey, Gorillas in the Mist (1983); J. Shreeve, Nature: The Other Earthlings (1987).
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