Eastern lowland gorilla

The eastern lowland gorilla, or Grauer's gorilla, is a critically endangered subspecies found only in the mountainous forests of eastern Democratic Republic of the Congo. It is the largest of all four gorilla subspecies. Its coat is jet black, like that of the mountain gorilla, but the hair on its head and body is shorter. As males age, their back fur turns grey, giving them the name "silverback." Key populations inhabit the Kahuzi-Biega and Maiko National Parks, the Tayna Gorilla Reserve, the Usala forest, and the Itombwe Massif.

This subspecies has a much smaller wild population than the western lowland gorilla. A 2004 report counted roughly 5,000 individuals, dropping to fewer than 3,800 by 2016. However, a 2021 survey estimated up to 6,800, suggesting the decline may not have been as severe as feared, though serious threats remain. Outside its native range, only one female eastern lowland gorilla lives in captivity, at Antwerp Zoo in Belgium.

Eastern lowland gorillas are the largest living primates. Based on a small sample, males weigh between [source omits specific range] and females [source omits specific range]; males stand between [source omits specific range] and females [source omits specific range]. An older weight for wild adult males is [source omits specific number]. They spend hours each day feeding on plant matter. Their diet includes fruits, leaves, stems, bark, and small insects like ants and termites, though insects are only a minor part. They do not eat banana fruit but may destroy banana trees for the nutritious pith. They prefer regenerating vegetation near abandoned villages and fields. Farmers who encounter gorillas in their plantations sometimes kill them, both to protect crops and to sell the meat.

This subspecies has the widest altitudinal range of any gorilla, living in mountainous, transitional, and lowland tropical forests. One well-studied population lives in the highlands of Kahuzi-Biega, where habitats range from dense primary forest to moderately moist woodland, Cyperus swamp, and peat bog. Compared to western lowland gorillas, eastern lowland gorillas travel less and eat more herbaceous vegetation.

Eastern lowland gorillas are highly sociable and peaceful, living in groups of two to over 30. A typical group has one silverback, several females, and their offspring. The silverback is the dominant leader and protects the group. Young silverback males eventually leave their birth group to attract females and form their own. Some groups include two full-grown males—about one-third of groups in East Africa have this structure. Most primates bond through female relationships, a pattern also seen in human families. Both females and males usually leave their group upon maturity. Females often join another group or a lone silverback, while males may stay together temporarily until they attract females. The group structure is thought to help prevent predation.

Relatively little is known about the social behavior, history, and ecology of eastern lowland gorillas, partly due to civil war in the Democratic Republic of the Congo. A female gives birth to a single infant after a gestation period of about [source omits specific number] months. Infants breastfeed for about three years, can crawl at around nine weeks, and walk at about 35 weeks. They stay with their mother for three to four years. Females mature at around eight years old, males at around twelve.

Threats include poaching, civil unrest, and habitat destruction from logging, mining, and agriculture. The primary cause of population decline is poaching for bushmeat. This meat is eaten by displaced people, militia groups, loggers, and miners. Surveys show that great apes—including chimpanzees and bonobos—make up 0.5–2% of meat in bushmeat markets. Some researchers estimate that up to [source omits specific amount] of bushmeat is traded annually. Because eastern lowland gorillas reproduce slowly and already have struggling populations, even a small proportion of bushmeat trade causes significant harm. Endangered Species International reports that 300 gorillas are killed each year to supply bushmeat markets in the Congo.