Eastern lowland gorilla

 

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Classification:

Global Population

Description and Natural History

Physical Description
There are three subspecies of eastern gorilla, one of which is the eastern lowland, or Grauer’s, gorilla (G.b. graueri). The other two subspecies of eastern gorilla are the mountain gorilla (G.b. beringei), and the Bwindi gorilla, an as yet unnamed subspecies from the Bwindi Impenetrable Forest. The eastern lowland gorilla has short black hair on the back and longer hair elsewhere on the body. Mature males have a silvery saddle on the back and are called “silverbacks”. Like other gorillas, the eastern lowland gorilla has small ears and broad nostrils. Adult males stand 175 cm (69 inches) tall and weigh 165 kg (360 lbs). Males are almost twice as large as females.

Natural History
The eastern lowland gorilla lives in the lowland and montane forests of the eastern Democratic Republic of the Congo (DRC). Like other gorillas, the eastern lowland gorilla has a well developed social structure and lives and travels in family groups. Each family group usually includes a dominant silverback, three unrelated adult females and four or five offspring. Subordinate males may also be found in the groups. Larger groups of 15-20 members, and even up to 30, have also been recorded. Females leave their birth groups to join other groups or single males when they reach sexual maturity at seven or eight years of age. The bonds between these unrelated adult females are loose, and only related females (e.g. mother/daughter, sisters) will groom one another. Adult females give birth to one baby about every four years although a surviving infant is produced only every six to eight years due to high infant mortality in the first three years of life. A baby gorilla is born weighing 1.8 - 2 kg (4 - 4.4 lbs) after a gestation period of 251-295 days. Babies are carried around by their mothers and begin to walk after 30-40 weeks. They are weaned at 2.5 to 3 years of age.

Males mature later than females and do not breed until 15 to 20 years of age. About half of all males leave their natal group at puberty and travel alone or with other subordinate males until they establish their own group. Once a male has established a group, he will most likely stay with that group for life unless he is ousted by another male. Fights for access to females among dominant silverbacks and lone males are intense and may result in death.

Eastern gorilla subspecies eat mostly leaves and other vegetation rather than fruit. They normally feed during the morning and afternoon and rest around midday. They make nests of branches and leaves at night, and scientists use nest and scat information collected from these sites to estimate the number of gorillas in a group and to determine their diet.

The population was estimated to number 3,000-5,000 individuals in 1980. Since that time civil war in the region has caused increased poaching and pressure on the gorillas and their habitats.

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Status of the Species

Status
The eastern lowland gorilla is listed as Endangered by the International Union for the Conservation of Nature and Natural Resources (IUCN). This species is also listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Eastern lowland gorillas are also protected under national wildlife legislation.

Threats to the Species
The eastern lowland gorilla is threatened by habitat loss, degradation and fragmentation from commercial logging and subsistence farming. A greater threat may be from poachers for the bushmeat trade. Civil unrest has severely threatened the gorillas and their habitat in Kahuzi-Beiga National Park, DRC, as rebels and poachers enter the park. Miners have also moved into the area to mine valuable ore known locally as “coltan”. Gorillas are also maimed or killed in snares (traps) set for other animals. Politics and poverty have also had a significant negative impact on gorilla conservation.

International Trade
Listed on CITES Appendix I which prohibits international trade.

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Authors and Sources

Sources IUCN. 2001. The 2000 IUCN Red List of Threatened Species. http://www.redlist.org. WWF. 1997. Eastern gorilla. http://www.panda.org. Harcourt, A.H. 2001. Gorillas. Pg 414-419 In MacDonald, D. (Ed). The New Encyclopedia of Mammals. Oxford University Press, Oxfordshire, UK.

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