Eastern Gorilla (Gorilla beringei): Mountain Gorilla Facts

What is an eastern gorilla?

Gorillas are great apes, close relatives of chimpanzees, bonobos and humans. Scientists recognize two gorilla species: the western gorilla of western Central Africa and the eastern gorilla, about 900 km (560 mi) farther east. Until the early 2000s all gorillas were usually treated as one species, but genetic studies showed that the eastern and western populations have been separate for a very long time.

The eastern gorilla has two subspecies:

• Mountain gorilla (Gorilla beringei beringei): lives in two small populations, one on the Virunga volcanoes where Rwanda, Uganda and DRC meet, and one in and around Bwindi Impenetrable National Park in Uganda.
• Grauer’s gorilla or eastern lowland gorilla (Gorilla beringei graueri): lives only in eastern DRC, from lowland rainforest to mountain forest, with important populations in Kahuzi-Biega and Maiko National Parks and the Itombwe Massif.

The species name honors Captain Robert von Beringe, a German officer who shot two gorillas on Mount Sabyinyo in the Virungas in 1902; the specimen was described as a new gorilla by Paul Matschie the following year.

What does an eastern gorilla look like?

Eastern gorillas are massively built, with a broad chest, short legs, very long arms and huge hands and feet. The face, palms, soles and chest of adult males are bare and black. The coat is darker than in western gorillas, usually jet black with a slight blue sheen, and lacks the reddish-brown cap often seen on western gorillas.

Mountain gorillas have the longest, thickest fur of all gorillas, an adaptation to cold, misty forests high on the volcanoes. Grauer’s gorillas have shorter, deep black hair. Both have a broad face with large nostrils, and each gorilla’s “nose print”, the pattern of wrinkles above the nostrils, is unique, which researchers use to identify individuals.

Adult males, called silverbacks, develop a saddle of silver-gray hair on the back from about 12 years of age. They also grow a tall bony crest on the skull that anchors their jaw muscles, giving the head a domed, conical shape, and long canine teeth.

How big is an eastern gorilla?

The eastern gorilla is the largest living primate. Males are roughly twice as heavy as females. Wild adult males usually weigh about 140–205 kg (310–450 lb) and stand about 1.6–1.8 m (5 ft 3 in–5 ft 11 in) tall when upright, with an arm span of up to about 2.3–2.7 m (7 ft 7 in–8 ft 10 in). Females weigh about 70–100 kg (155–220 lb) and stand about 1.5 m (4 ft 11 in) tall.

Grauer’s gorilla is the largest gorilla of all. The tallest wild gorilla on record, a male shot in North Kivu in 1938, measured about 1.95 m (6 ft 5 in). Sample sizes for wild weights are small, so these figures are approximate. For more, see How much does a gorilla weigh?

Where do eastern gorillas live?

Eastern gorillas live in a small part of the Albertine Rift region of east-central Africa. Mountain gorillas in the Virunga Mountains live on the slopes of dormant volcanoes in Volcanoes National Park (Rwanda), Virunga National Park (DRC) and Mgahinga Gorilla National Park (Uganda), mostly between about 2,200 and 3,800 m (7,200–12,500 ft), in bamboo forest, Hagenia woodland and subalpine vegetation. The Bwindi population lives lower, in steep, densely forested hills of about 1,200–2,600 m (3,900–8,500 ft).

Grauer’s gorillas have the widest elevation range of any gorilla, from lowland rainforest at about 600 m (2,000 ft) up to mountain and bamboo forest above 2,500 m (8,200 ft). Their range lies east of the Lualaba River in eastern DRC, but they now occupy only a fraction of the area they used a few decades ago. Compare the ranges of all four gorilla subspecies in Where do gorillas live?

What do eastern gorillas eat?

Eastern gorillas are mainly herbivores. Mountain gorillas in the Virungas live almost entirely on leaves, shoots, stems and pith, which make up more than 85 percent of their diet; fruit makes up only about 2 percent. Researchers have recorded around 140 plant species in their diet, including wild celery, thistles, nettles, bedstraw vines and bamboo shoots, plus bark, roots, flowers, fungi and the occasional insect.

Gorillas in Bwindi and Grauer’s gorillas eat more fruit when it is available. An adult male mountain gorilla can eat around 18–19 kg (40–42 lb) of plant food a day, and a female around 15 kg (33 lb). Because leafy food is plentiful, eastern gorillas usually travel shorter distances each day than fruit-seeking western gorillas, often less than 1 km (0.6 mi).

Family life and behavior

Eastern gorillas live in stable groups led by a dominant silverback. Groups average about 10 animals but range from a few to more than 30. A typical group has the leading silverback, several adult females, their young, and sometimes one or more younger males. In the Virungas, about a third of mountain gorilla groups contain more than one adult male, usually relatives of the leader.

The silverback decides where the group goes, settles quarrels and defends the group against rival males and predators. Most young males leave their birth group at about 11 years old and may live alone or in all-male groups for some years before attracting females. Around 60 percent of females also move to another group, often at about 8 years old.

Gorillas are active by day. They feed in the morning and afternoon and rest around midday, when youngsters wrestle, chase and play. Each evening every adult builds a new nest of bent plants, usually on the ground in mountain gorillas, and infants sleep with their mothers. Mountain gorillas have around 25 recognized calls, from contented rumbling belches to barks and roars. Threatened silverbacks put on dramatic displays that end with a charge, but serious fights are rare. Learn more in Why do gorillas beat their chests?

Reproduction and lifespan

Eastern gorillas breed at any time of year. After a pregnancy of about eight and a half months, a female gives birth to a single infant weighing around 2 kg (4.4 lb). The baby clings to its mother, rides on her back from a few months old and is not fully weaned until about three to four years of age.

Females usually have their first infant at about 10 years old and then give birth only about once every four years. A female may raise just a handful of surviving offspring in her life, which means gorilla populations grow very slowly even when they are well protected. Wild eastern gorillas typically live about 35–40 years.

Threats

Adult eastern gorillas have few natural predators; leopards may occasionally take a young or weak gorilla. The main threats come from people:

• Snares and poaching: Grauer’s gorillas are hunted for bushmeat, especially around mining camps, while mountain gorillas are mostly caught in snares set for antelopes.
• Habitat loss: farming, charcoal production, logging and mining, including small-scale mining for minerals such as coltan, have cleared and fragmented forests.
• War and insecurity: decades of armed conflict in eastern DRC have made protection difficult, and many park rangers have been killed on duty.
• Disease: gorillas can catch human respiratory infections, a particular risk for habituated groups that see tourists and researchers every day.

Conservation status

The IUCN Red List classifies the eastern gorilla as Critically Endangered, with a decreasing population. It was moved to this category in 2016 after surveys showed that Grauer’s gorillas had declined by roughly 77 percent since the mid-1990s, from about 17,000 to an estimated 3,800. A later survey suggested there could be up to about 6,800, but the subspecies remains under heavy pressure.

Mountain gorillas are a rare success story. From a low of about 250 in the Virungas in 1981, numbers have risen to more than 1,000 thanks to anti-poaching patrols, veterinary care and income from tourism, and in 2018 the mountain gorilla subspecies was moved from Critically Endangered to Endangered. Read the full story in How many mountain gorillas are left? The species is listed on CITES Appendix I, which bans international commercial trade.

Myths and facts

Myth: gorillas are violent monsters. Field studies beginning with George Schaller in 1959 and Dian Fossey from 1967 showed that mountain gorillas are mostly peaceful, gentle animals. Chest-beating and charges are usually bluffs intended to avoid a fight.

Myth: gorillas eat bananas all day. Wild mountain gorillas eat very little fruit; their diet is mostly leaves, stems and pith. See What do gorillas eat?

Myth: all gorillas are the same. Eastern and western gorillas are separate species that differ in coat color, size, diet and group structure.

Gorillas and people

Mountain gorillas became world-famous through the work of Dian Fossey, whose Karisoke Research Center in Rwanda has studied them since 1967, and through her book Gorillas in the Mist. Today, carefully controlled gorilla tracking in Rwanda, Uganda and DRC lets small groups of visitors spend one hour with habituated families. Permits are expensive, for example US$1,500 per person in Rwanda, and the money funds park protection and local communities.

Eastern gorillas are almost absent from zoos: mountain gorillas are not kept in captivity at all, and orphans rescued from poachers are cared for in sanctuaries in DRC, such as the Senkwekwe Center in Virunga National Park and the GRACE center for Grauer’s gorillas.