The Eastern gorilla is the largest primate in the world. As compared with other gorillas, the Eastern gorilla has smaller nose, shorter arms, longer hair as well as larger jaws and teeth. Mature males are often called silverbacks due to a large patch of hair on their backs, which is silver of grey in color. In addition, males have sharp and large canine teeth. When under stress, apocrine glands in the armpits of females emit a strong smell. The arms of Eastern gorilla are long and muscular, head is huge and legs are short. The silky and long coat of this primate varies from blue-black to brownish grey.
There are two recognised subspecies of eastern gorilla: the mountain gorilla restricted to the mountain rainforests and subalpine forests of eastern Democratic Republic of the Congo, southwestern Uganda and Rwanda; and Grauer's gorilla occurring across the forests of the Albertine Rift in eastern Democratic Republic of Congo.
They are diurnal, spending 40% of the day resting, 30% travelling and another 30% - feeding. They rest and sleep in nests, placed on steep slopes, in trees or on the ground. Eastern gorillas gather in social units called harems, which contain a male and females with their young. Gorilla harems are not territorial, though conflicts and encounters can happen, particularly when a lone male gets into contact with members of the harem. Grooming is a common activity for these gorillas, usually occurring between males and females as well as among females. These animals are very calm, careful to their babies, forming strong bonds within the group. Eastern gorillas use a wide variety of communication forms, interacting with each other or warning intruders to keep away.
Eastern gorillas are folivores, feeding mainly upon leaves, roots, stems, vines, shrubs, bamboo as well as pith of herbs. They also consume flowers, fruit, berries, fungi, wood, bark of trees and epithelium, which is stripped from roots. In addition, these primates will sometimes eat invertebrates.
These animals have polygynous mating system with the dominant male of the group having exclusive right of mating with all females of the group. The Eastern gorillas mate all year round. The gestation period lasts 8.5 month, yielding a single, dependent baby. The infant is carried by its mother, able to crawl only at 9 weeks old and starting to walk at the age of 30-40 weeks. The mother breastfeeds the young for about 1 year, though weaning often occurs no sooner than 3 years old. After weaning, the young continue living with their mother for another year. Female gorillas reach sexual maturity at 10 years old while males don't breed until they are at least 15 years old.
Poaching is among the major threats to this species’ population. The Eastern gorillas are poached for their body parts while juveniles are captured by zoos and private collectors. Another notable threat is the civil war in the region, which has caused a number of fatal accidents. Tourism, which so far supported survival of the Eastern gorillas, has recently become a threat due to a large number of people coming into contact with these animals and thus putting them at risk of catching a human disease.
The overall number of their population is suspected to be fewer than 5,000 individuals, though presently decreasing. On the IUCN Red List, the Eastern gorilla is classified as Critically Endangered (CR) species.
Feeding upon vegetation, these primates play important role for plant communities. Due to consuming plants, these gorillas become seed dispersers, helping many large fruit trees survive.