Mountain gorilla

 

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Classification:

Global Population

Description and Natural History

Physical Description
Adult mountain gorillas are black in color, with relatively long, silky hair. As males reach maturity, they begin to grow a silvery-white saddle on their backs which extends to their rump and thighs. Such individuals are called “silverbacks.” Silverback males may weigh more than 200 kilograms (440 pounds) and are 1.7 – 1.8 meters (5.6 – 5.9 feet) tall when standing. Females are smaller, weighing up to 100 kilograms (220 pounds). The arm span is about 234 centimeters (more than seven feet).

Natural History
Mountain gorillas live in the mountainous rainforests of central Africa; about 320 individuals live on the extinct volcanoes forming the Virunga Range on the borders of Rwanda, Uganda and the Democratic Republic of Congo (DRC, formerly Zaire).

Most gorillas range within the Virunga National Park in the DRC and Volcans National Park in Rwanda. A few are also found in Mgahinga National Park in Uganda. About 292 mountain gorillas live in Bwindi Impenetrable National Park in southwest Uganda on the border of the DRC.

Gorillas walk on all fours, with the weight of their upper bodies carried on the backs of their knuckles. They rarely stand on their hind limbs except during chest-beating displays.

Like other gorilla species, mountain gorillas live and travel in family groups of five to thirty individuals. Mountain gorilla social units usually consist of one dominant silverback (the leader), one or two black-backed sub-adult males, several adult females, and up to ten offspring, juveniles and infants. Family units are usually peaceful. Only the silverback mates with the females. Maturing silverbacks (age 11 – 13 years) that are no longer tolerated by the dominant silverback leave the group and may live on their own before luring females from other natal groups to begin their own family groups.

Females reach sexual maturity between seven and eight years of age and give birth for the first time a few years later. Males do not usually breed until at least 15 years of age. Gestation lasts about 258 days. Females usually give birth every 3.5 to 4.5 years to a single offspring. Young are weaned at two years of age, but some continue to suckle until the next birth. Infants cling upside down holding onto the long chest hairs of their mother until they are about four months old. At this time, they begin to ride on the back.

Mountain gorillas have a home range of between five and 30 square kilometers (1.9 to 11.6 square miles) in which they feed on stems, shoots, fruits, bark, bamboo, wild celery and ants, snails and slugs. Mountain gorillas are mostly ground-dwelling but will feed and build nests in trees that can support their weight.

The total mountain gorilla population is estimated to be 647 animals. Gorillas may live 35 years in the wild.

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Status of the Species

Status
The mountain gorilla is listed as Critically Endangered by the International Union for the Conservation of Nature and Natural Resources (IUCN). The species is also listed on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). In addition, mountain gorillas are listed on Class A of the African Convention on the Conservation of Nature and Natural Resources (1969).

Threats to the Species
Mountain gorillas are threatened by habitat loss due to logging for subsistence agriculture and commercial purposes. Logging opens up forests, giving poachers easy access to animals for the bushmeat trade, which may now be more of a threat than habitat loss or degradation.

Young gorillas are also captured for sale to zoos and research institutions. Civil wars in Rwanda and the DRC during the 1990s led to gorilla deaths and loss of habitat. Large numbers of human refugees fled to camps at the edge of Virunga National Park, which led to uncontrolled firewood harvesting and increased poaching in the Park.

The establishment of buffer zones around the parks and appropriate management within them is urgently required to protect the remaining gorillas. Cooperation between countries where mountain gorillas are found is also required. Lack of funds to employ wildlife wardens and the inaccessibility of many of the areas make enforcement almost impossible.

Gorillas are frequently maimed or killed in illegal traps or snares set for other forest animals. Controlled tourism to view habituated groups of mountain gorillas provides much-needed revenue for the Parks and for gorilla protection efforts, including enforcement. Due to civil unrest, visits to Rwanda are not recommended at present, but gorilla groups can be safely accessed from Uganda and the DRC.

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

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Authors and Sources

Sources
CITES. 2001. Western lowland gorilla. http://www.cites.org.

Dian Fossey Gorilla Fund. 2001. Gorilla facts. http://www.gorillas.org.

IUCN. 2001. The 2000 IUCN Red List of Threatened Species. http://www.redlist.org.

Knight, T. 2001. Gorilla natural history. Gorillas Online. http://staff.washington.edu/timk/gorillas/info/nh.html.

WCMC and WWF. 2001. Gorillas. http://www.panda.org.

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