Western gorilla  (Gorilla gorilla)

The western gorilla is classified as Critically Endangered (CR) on the IUCN Red List (1), and listed on Appendix I of CITES (3).

The gorilla is a heavily built primate and is the largest of the living apes. 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 a characteristic body shape with a broad chest, heavy neck and strong hands and feet. They have a fine, brownish coat, often with a red or auburn tinge on the crown, and mature males are known as 'silverbacks' due to the silvery-white saddle of hair extending from the back to the rump and thighs (2). Male gorillas have a larger skull crest than females and other apes, together with larger canines and a more pronounced ridge above the eyes (2). Western gorillas are smaller and lighter bodied than eastern gorillas, because they must be agile climbers in order to reach fruits in the trees (2).

The two subspecies of western gorilla differ markedly in their range and abundance. The Cross River gorilla (Gorilla gorilla diehli) is the most restricted of the gorillas, being found only in a few isolated populations on the Nigerian-Cameroon border (5). In contrast, the western lowland gorilla (Gorilla gorilla gorilla) is the most widespread, being found in areas of Cameroon, the Central African Republic, Congo, Gabon, Equatorial Guinea, and the Cabinda enclave of Angola (6).

The western gorilla inhabits primary, secondary, and swamp forests (2).

Western gorillas live in groups that vary in size between 2 and 20 individuals, composed of at least one male, several females and their offspring (2). A dominant male silverback heads the group, with younger males usually leaving the group when they reach maturity. Females transfer to another group before breeding, which begins at eight to nine years old; they care for their young infant for the first four to five years of its life (2). There is therefore a long interval between births, which partly explains the slow population growth rates that make the western gorilla so vulnerable to poaching (6). Due to the long gestation time, long period of parental care, and infant mortality, a female gorilla will only give birth to an offspring that survives to maturity every four to six years. Gorillas are long-lived and may survive for as long as 40 years in the wild (4).

Fruit forms a large part of the western gorilla's diet and they will travel further each day in search of fruiting trees than their eastern relatives (2). The distance that gorillas travel each day while they are searching for fruit trees varies between one and four kilometres. A group's home range may be as large as 30 square kilometres (2).

The decline in gorilla numbers is mainly attributed to the loss and degradation of their forest habitat, which has been relentlessly cleared to make way for agricultural and logging practices, and to the Ebola virus (6). From 1992 to 2007, it is thought that around one third of the total population found in protected areas was killed by this lethal virus (1). Increasingly, the trade in bushmeat is posing more of a threat to the survival of the species and cleared forests are ever more accessible to hunters. The demand for meat has increased from both road labourers and a growing urban market (7). Western gorillas are very susceptible to the illegal bushmeat trade, as gorilla meat is viewed as a symbol of wealth and prestige (8). Male gorillas will actively defend their females and offspring if their group encounters a threat, and this increases their chances of being killed by a hunter (8).

The western gorilla is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES) (3), and there has been a decline in international trade of the species (4). The United Nations Environmental Program (UNEP) has recognised the urgent need to protect our closest relatives and has established a Great Ape Survival Project (GRASP) 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).

View information on this species at the UNEP World Conservation Monitoring Centre.

Learn more about western gorilla conservation:

• Great Apes Survival Project (GRASP):
  www.unep.org/grasp
• Berggorilla & Regenwald Direkthilfe:
  www.berggorilla.org/english/frame.html

For more information on the western gorilla:

• BBC Wildlife Finder: 
  http://www.bbc.co.uk/nature/species/Western_Gorilla
• EDGE of Existence:
  http://www.edgeofexistence.org/mammals/species_info.php?id=161