The Mountain Gorilla (Gorilla beringei beringei) is one of two subspecies of Eastern Gorillas. It is only found in the Virunga volcanic mountains of Central Africa, within three national parks: Mgahinga, in south-west Uganda; Volcanoes, in north-west Rwanda; and Virunga, in the eastern Democratic Republic of Congo (DRC). Some claim that the Bwindi population in Uganda's Bwindi Impenetrable Forest is a third subspecies, although no formal taxonomic description has been published.
The Mountain Gorilla has longer and darker hair than other gorilla species, enabling it to live at high altitudes and travel into areas where temperatures drop below freezing. It has adapted to a life on the ground more than any other non-human primate, and its feet most resemble those of humans. Gorillas can be identified by nose prints unique to each individual; researchers often use photographs and illustrations of noses for identification and monitoring.
The Mountain Gorilla, like all gorillas, is highly sexually dimorphic, with males usually weighing twice as much as females. Adult males also have more pronounced bony crests on the top (sagittal) and back (nuchal) of their skulls, giving their heads a more conical shape. These crests anchor the massive muscles of their large jaws. Adult females also have these crests, but they are much less pronounced.
Adult males are called silverbacks. When they reach sexual maturity, a saddle of gray or silver-colored hair develops on their backs. The hair on their backs is shorter than on most other body parts, and their arm hair is especially long. Upright, males reach 1.5–1.8 m (5–6 ft) in height, with an arm span of 2.25 m (7 ft 6 in) and weigh 204–227 kg (450–500 lb).
The Mountain Gorilla is primarily terrestrial and quadrupedal. However, it will climb into fruiting trees if the branches can carry its weight, and it is capable of running bipedally up to 6 m (20 ft). Like all great apes other than humans, its arms are longer than its legs. It moves by knuckle-walking (like the Common Chimpanzee, but unlike the Bonobo and both orangutan species), supporting its weight on the backs of its curved fingers rather than its palms.
The Mountain Gorilla is diurnal, most active between 6:00 a.m. and 6:00 p.m. Many of these hours are spent eating, as large quantities of food are needed to sustain its massive bulk. It forages in early morning, rests during the late morning and around midday, and in the afternoon it forages again before resting at night. Each gorilla builds a nest from surrounding vegetation to sleep in, constructing a new one every evening. Only infants sleep in the same nest as their mothers. They leave their sleeping sites when the sun rises at around 6 am, except when it is cold and overcast; then they often stay longer in their nests.