Endangered species
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| Gorilla facts and key issues |
Key issues | Facts
Key issues
Habitat loss is a major threat to gorillas as forests are rapidly being lost to commercial logging interests and subsistence agriculture. There is also a strong link between habitat loss and the bushmeat trade, as forests opened up by timber companies are more easily accessible to hunters, who often sell meat to employees of the logging companies.
Read more on logging in Africa
The commercial trade in bushmeat, which occurs throughout west and central Africa, may now be more of a threat to African primates than habitat loss and degradation, but the number of gorillas killed annually is unknown. Estimating numbers of gorillas poached is difficult because they are often butchered and eaten on the spot, or their meat is smoked for later sale in towns.
Although the great apes constitute only a small proportion of the total species killed for the bushmeat trade, they present easy targets for hunters, and in some areas such as eastern Cameroon, gorillas are favoured by hunters because of the weight of saleable meat. Gorillas are frequently maimed or killed throughout their range by traps and snares intended for other forest animals such as antelope.
Read more on the bushmeat trade
Exposure to human diseases is a potential threat to gorillas. This particularly affects groups of habituated gorillas that come in close contact with humans in areas where gorilla tourism is promoted. In late 2002 an outbreak of Ebola hemorrhagic fever was reported in the north of the Republic of Congo on the border with Gabon. By late February 2003, 80 cases had been reported in northern Congo, including 64 deaths. Most cases were in the district of Kéllé. The human infections coincided with a large-scale die-off of great apes in the region. Before the current crisis, up to 110,000 western lowland gorillas (Gorilla gorilla gorilla) were thought to remain in central Africa, the area currently affected by Ebola. Now, in some areas, more than 90 per cent of western lowland gorilla have been killed. For example, in Lossi Gorilla Sanctuary in Congo, in late 2002, 136 out of 143 gorillas disappeared, apparently as a result of Ebola. The disease continues to spread and is now reported in Odzala National Park, a site known to have the highest density of great apes in Africa.
In February 2003, two Spanish primatologists reported that all 139 gorillas in their study area had succumbed to the disease within two months. Ebola adds yet another threat to those already facing these species, such as deforestation and the wild meat trade.
Read more on Ebola
Facts
- There are two species of gorilla: the western gorilla (gorilla gorilla) and the eastern gorilla (gorilla beringei).
- There are two subspecies of western gorilla: western lowland gorilla (gorilla gorilla gorilla) and the Cross River gorilla (gorilla gorilla diehli). There are two subspecies of eastern gorilla: the eastern lowland or Grauer's gorilla (gorilla beringei graueri) and the mountain gorilla (gorilla beringei beringei).
- The IUCN status and population figures of the four subspecies of gorilla is:
- Western lowland gorilla: Endangered (111,000)
- Cross River gorilla: Critically Endangered (200)
- Eastern lowland/Grauer's gorilla: Endangered (3,000-5,000 in 1980)
- Mountain gorilla: Critically Endangered (650)
- The western gorilla occurs in the rainforests of Central Africa. The Cross River gorilla is restricted to forested hills on the Nigerian-Cameroon border, more than 250km from the nearest population of western lowland gorillas. It is categorised as Critically Endangered owing to its low numbers and fragmented populations. Perhaps no more than 200 survive, in small isolated populations separated by densely settled farmlands.
- The western lowland gorilla is the most widespread of all the gorilla subspecies, ranging through southern Cameroon, the south-west corner of the Central African Republic, west Congo (Brazzaville), Equatorial Guinea, Gabon, and southwards to the Cabinda enclave of Angola (north of the Zaire River).
There is no reliable estimate of the total numbers of western lowland gorillas because they inhabit thick rainforest where it is difficult to count them. The forests of Gabon are considered to harbour the major population, although it is possible that unsurveyed areas of Congo (Brazzaville) may contain equivalent numbers. Surveys in Gabon have established that western lowland gorillas occur at higher densities throughout a wider range of forest habitats than was previously thought. The total western lowland gorilla population in central Africa may number as many as 110,000. Nevertheless, the western lowland gorilla is categorised as Endangered because of habitat loss and poaching pressure; the population in Equatorial Guinea is probably Critically Endangered.
- The eastern lowland/Grauer's gorilla occurs in the lowland and Albertine Rift montane forests of the eastern Democratic Republic of Congo (DRC, formerly Zaire), approximately 1,000km from the nearest populations of western lowland gorillas. There is no reliable estimate of the total numbers of Grauer's gorillas. Their population density varies from area to area, and population estimates are extremely difficult to make in forest habitats. In 1980 the subspecies was estimated at 3,000-5,000, all in the DRC, but because it lives in a civil war area, it is facing unprecedented poaching pressure.
- The population of the mountain gorilla is believed to be around 650 - and is likely to be accurate, as these animals have been intensely monitored since the 1950s. The mountain gorilla inhabits Africa's troubled Great Lakes region, where armed conflict has raged for more than a decade. A population of about 355 mountain gorillas occurs on the extinct volcanoes forming the Virunga Range along the borders of Rwanda, Uganda and DRC. Most of these gorillas range within the Virunga National Park, DRC, and the Volcans National Park, Rwanda, while a few use the Mgahinga National Park in Uganda. A separate population of about 292 mountain gorillas is found in the nearby Bwindi-Impenetrable National Park in south-west Uganda, on the border with the DRC.
- The western lowland gorilla has a brownish-grey coat with a red or auburn crest. The Cross River gorilla differs from the western lowland subspecies in skull and tooth dimensions. The eastern gorilla is dark in colour. The mountain gorilla differs from the lowland subspecies in having longer hair, jaws and teeth, and slightly shorter arms.
- Adult males gorillas have a silvery white saddle extending from the back to the rump and thighs and are called "silverbacks".
- Gorillas have a well-developed social structure, living and travelling in family groups which vary from 2 to 35 individuals, but more typically number 5 to 10. Gorillas have a home range of between 5 to 30 sq km and are mainly herbivorous, feeding on stems, shoots and fruit supplemented with bark and invertebrates. A group of gorillas typically consists of a single dominant "silverback" male, three adult females, and four or five offspring.
- Nearly all female gorillas leave their natal group at maturity to join other groups or single males. Females become sexually mature at seven to eight years old but do not start to breed until around ten years. Males mature later than females, with few breeding before the age of 15. High infant mortality, a long gestation period (251-295 days), a tendency to single births, and a prolonged period of maternal care, mean that on average only one infant is reared in a six to eight-year period.
- Gorillas eat large amounts of vegetation from more than 70 different plant species - including, for large males, up to 33kg of bamboo a day.
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WWF-UK > Research > Issues > Species > Gorillas - Facts and key issues
