The mountain gorilla (Gorilla beringei beringei) is one of the two subspecies of the eastern gorilla. It is listed as endangered by the IUCN as of 2018.

There are two populations: One is found in the Virunga volcanic mountains of Central/East Africa, within three National Parks: Mgahinga, in southwest Uganda; Volcanoes, in northwest Rwanda; and Virunga, in the eastern Democratic Republic of Congo (DRC). The other population is found in Uganda's Bwindi Impenetrable National Park. Some primatologists speculate the Bwindi population is a separate subspecies, though no description has been finalized. As of June 2018, there were more than 1,000 individuals.

Gorilla taxonomy

Mountain gorillas are descendants of ancestral monkeys and apes found in Africa and Arabia during the start of the Oligocene epoch (34–24 million years ago). The fossil record provides evidence of the hominoid primates (apes) found in east Africa approximately 22–32 million years ago. The fossil record of the area where mountain gorillas live is particularly poor and so its evolutionary history is not clear.

It was about 8.8 to 12 million years ago that the group of primates who were to evolve into gorillas split from their common ancestor with humans and chimps; this is when the genus Gorilla emerged. Mountain gorillas have been isolated from eastern lowland gorillas for approximately 10,000 years and these two taxa separated from their western counterparts approximately 1.2 to 3 million years ago. The genus was first referenced as Troglodytes in 1847, but renamed to Gorilla in 1852. It was not until 1967 that the taxonomist Colin Groves proposed that all gorillas be regarded as one species (Gorilla gorilla) with three subspecies Gorilla gorilla gorilla (western lowland gorilla), Gorilla gorilla graueri (lowland gorillas found west of the Virungas) and Gorilla gorilla beringei (mountain gorillas, including Gorilla beringei, found in the Virungas and Bwindi). In 2003, after a review, they were divided into two species (Gorilla gorilla and Gorilla beringei) by The World Conservation Union (IUCN). There is now agreement that there are two species, each with two subspecies.

The fur of the mountain gorilla, often thicker and longer than that of other gorilla species, enables them to live in colder temperatures. Gorillas can be identified by nose prints unique to each individual

Males reach a standing height of 161–171 cm (63–67 in), a girth of 138–163 cm (54–64 in), an arm span of 2 to 2.7 m (6 ft 7 in to 8 ft 10 in) and a weight of 120–191 kg (265–421 lb). Females are smaller with a weight of 70–98 kg (154–216 lb).[10] This subspecies is smaller than the eastern lowland gorilla, the other subspecies of eastern gorilla. Adult males have more pronounced bony crests on the top and back of their skulls, giving their heads a more conical shape. These crests anchor the powerful temporalis muscles, which attach to the lower jaw (mandible). Adult females also have these crests, but they are less pronounced. Like all gorillas, they feature dark brown eyes framed by a black ring around the iris. Adult males are called silverbacks because a saddle of gray or silver-colored hair develops on their backs with age. The hair on their backs is shorter than on most other body parts, and their arm hair is especially long. Fully erect males can reach 1.7 m (5 ft 7 in) in height, with an arm span of 2.3 m (7 ft 7 in) and weigh 155 kg (342 lb). The tallest silverback recorded was 1.95 m (6 ft 5 in) tall with an arm span of 2.7 m (8 ft 10 in), a chest of 1.98 m (6 ft 6 in), and a weight of 219 kg (483 lb), shot in Alimbongo, northern Kivu in May 1938. There is an unconfirmed record of another individual, shot in 1932, that was 2.06 m (6 ft 9 in) and weighed 218.6 kg (482 lb). The heaviest silverback recorded was a 267 kg (589 lb) 1.83 m (6 ft 0 in) tall specimen shot in Ambam, Cameroon.

The mountain gorilla is primarily terrestrial and quadrupedal. However, it will climb into fruiting trees if the branches can carry its weight. Like all great apes other than humans, its arms are longer than its legs. It moves by knuckle-walking, supporting its weight on the backs of its curved fingers rather than its palms.

The mountain gorilla is diurnal, spending most of the day eating, as large quantities of food are needed to sustain its massive bulk. It forages in the 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.

The mountain gorilla inhabits the Albertine Rift montane cloud forest, including the Virunga Mountains, ranging in elevation from 2,200 to 4,300 m (7,200 to 14,100 ft). Most groups live on the slopes of three of the dormant volcanoes: Karisimbi, Mikeno, and Visoke. The vegetation is very dense at the bottom of the mountains, becoming more sparse at higher elevations, and the forests are often cloudy, misty and cold.

The home range used by one group of gorillas during one year is influenced by availability of food sources and usually includes several vegetation zones. George Schaller identified ten distinct zones, including: bamboo forest at 2,200–2,800 m (7,200–9,200 ft); Hagenia forest at 2,800–3,400 m (9,200–11,200 ft); and the giant senecio zone at 3,400–4,300 m (11,200–14,100 ft). The mountain gorilla spends most of its time in Hagenia forest, where galium vines are found year-round. All parts of this vine are consumed: leaves, stems, flowers, and berries. It travels to the bamboo forest during the few months of the year when fresh shoots are available, and it climbs into subalpine regions to eat the soft centers of giant senecio trees.