Eastern Gorilla

Eastern gorillas live in stable, cohesive family groups, led by a dominant silverback male. Eastern gorillas tend to have larger group sizes than their western relatives, exceptionally numbering more than 50 individuals (2). There is no distinct breeding season and females give birth only once every three to four years due to the gestation period of 8.5 months and a long period of parental care. Newborn gorillas have greyish-pink skin and can crawl after nine weeks; they are not fully weaned until 3.5 years (2). Males defend their females and offspring using their large size in intimidating displays involving charging and chest-beating (2). Eastern gorillas are herbivorous, with a heavily foliage-based diet (2). They have smaller home ranges than western gorillas as foliage is more abundant than fruit. They are diurnal but most foraging occurs in the morning and late afternoon. At night they build nests by folding over vegetation, usually on the ground (2).

The mountain gorilla occurs mainly within national parks and in some areas is protected by armed guards to prevent poaching (7). Gorillas in the Virunga region have been studied and protected for many decades and are now seen as an important source of tourist revenue (8). The United Nations Environmental Programme (UNEP) has recognised the urgent need to protect our closest relatives and has established a Great Ape Survival Project (GRASP). This project is aimed at identifying the conservation initiatives required to secure the future of the apes and at obtaining political support and funding to allow these to be achieved (9). A multifaceted approach is needed to ensure the survival of one of our most impressive cousins.

The largest of the living apes, the gorilla has a characteristically heavy body shape and shaggy dark coat. Until recently it was considered a single species, but DNA evidence has led to the recognition of the eastern and western populations as distinct species; Gorilla beringei and Gorilla gorilla respectively (4). Gorillas have robust bodies with broad chests and long arms. The mountain gorilla subspecies (Gorilla beringei beringei) has a particularly long coat, which is blue-black to brownish-grey in colour. Mature male gorillas are much larger than females with a large skull crest. At about 14 years old, the hair in the saddle of their back turns white and hence they are known as 'silverbacks' (2). Gorillas are quadrupedal, walking on the knuckles of their forelimbs and the soles of their feet (2).

The eastern gorilla inhabits tropical forest. Mountain gorillas are found at altitudes between 1,160 and 4,100 metres while eastern lowland gorillas occur between 600 and 2,900 metres above sea level (5).

The best known of the eastern gorillas, the mountain gorilla, is found in two isolated populations. One is in the Virunga Volcanoes region, situated on the borders of Rwanda, Uganda and the Democratic Republic of Congo (DRC). The other occurs in Bwindi Impenetrable National Park in southwestern Uganda (1). The Virunga population was estimated to comprise 380 individuals in 2003, while there were estimated to be just 300 individuals in the Bwindi population in 2006 (1). The eastern lowland or Grauer's gorilla (G. b. graueri) is found only in eastern DRC, and is significantly more abundant than the mountain gorilla (1).

Classified as Endangered (EN) on the IUCN Red List (1), and listed on Appendix I of CITES (3).

Snares set to trap other wildlife may accidentally maim and even kill gorillas (6), while poaching for infants has re-emerged as a threat to mountain gorillas (1). The biggest threats to Grauer's gorillas result from armed conflict in and around the parks. In the past decade, many Grauer's gorillas have been shot dead in crossfire, or for food by people hiding in the forest. Ongoing instability in the region means that this problem is getting worse, as civil war has made arms more accessible and continues to create large numbers of refugees (7). A relatively new threat to the gorillas comes from the tourism. While tourism has so far aided its survival, large numbers of people coming into close contact with gorillas may put them at risk from human diseases (7).