Western gorillas are critically endangered in the wild. Population estimates for G. gorilla are unavailable, but are almost certainly less than the often cited figure of 95,000. Estimates of G. gorilla diehli populations are from 250 to 300 individuals.
Even though all eight countries with wild gorilla (Gorilla) populations have laws governing their capture and hunting, in none of them are the laws strictly enforced. As recently as fifteen years ago, there was active trade in gorilla skulls from the Volcano National Park in Rwanda. Today, countries such as Rwanda are implementing educational, conservation, and tourism programs in an effort to demonstrate to the local population the value of the native flora and fauna. Still, long-term ecological stability is sacrificed for shorter term economical gain in many areas. Nevertheless, hunting is a relatively minor concern compared to deforestation and the effects of political unrest.
The forests which the gorillas depend on in Africa are slowly being cut down for timber and to make way for agricultural and, in some cases, industrial development. As a case in point, Nigeria was home to gorillas twenty-five years ago. Today, gorillas have become extinct there and cattle-ranches cover what used to be gorilla habitat. Until human population growth is curbed in central Africa, particularly DRC, gorilla habitat is in danger of shrinking yet further and becoming dangerously scarce.
US Federal List: endangered
CITES: appendix i
IUCN Red List of Threatened Species: critically endangered
Predation upon gorillas is probably not common, due to their imposing size. Young animals may fall prey to raptors or large carnivores. Also, gorillas that have not yet been weaned are subject to infanticide by males of their species.
Western gorillas are exceptionally large and powerful primates. They have no tails and jet black skin. Facial features include short muzzles, a prominent brow ridge, large nostrils, and small eyes and ears. Western gorillas have large jaw muscles and broad, strong teeth. Coarse, dark hair covers the entire body except for the face, ears, hands, and feet. Generally, the hair on the back and rump of older males grows grey and is lost with age. This coloration pattern has resulted in older males being known as "silverbacks". Western gorillas have a slightly more brown/grey coat color with shorter hair and are usually slightly smaller than mountain gorillas (G. beringei).
Males are usually larger than females, reaching weights up to 275 kg in captivity. In the wild, male gorillas average 180 kg, with females often almost half that weight. Male gorillas have stocky bodies standing usually 1.75 meters in height with bent knees. On average, females are only 1.25 meters tall. This marked sexual dimorphism is critical in group structure and mating. Large males, with large body size, canines, and jaw musculature, have increased physical and social power within the group.
Hands are proportionately large with nails on all digits and very large thumbs. Western gorillas frequently stand upright, but walk in a hunched, quadrupedal fashion, with hands curled and knuckles touching the ground. Walking quadrupedally requires long arms, and the armspan of gorillas is larger than their standing height. Limbs are plantigrade and pentadactyl.
Range mass: 275 (high) kg.
Average mass: 180 kg.
Average wingspan: males 175 cm; females 125 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently
Wild gorillas live between 35 and 40 years with some captive gorillas living almost 50 years.
Range lifespan
Status: wild: 35 to 40 years.
Range lifespan
Status: captivity: 50 (high) years.
Average lifespan
Sex: female
Status: captivity: 47.0 years.
Average lifespan
Status: captivity: 39.3 years.
Average lifespan
Status: wild: 47.0 years.
Average lifespan
Status: captivity: 40.0 years.
Average lifespan
Status: wild: 50.0 years.
Average lifespan
Status: captivity: 54.0 years.
Africa's tropical secondary forests, where the open canopy allows much light to reach the forest floor, provide the best habitat for western gorillas.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: forest ; rainforest
Western or lowland gorillas inhabit the forests of equatorial Africa from the western lowlands near the Cameroon coast through the Central African Republic, Equatorial Guinea, Gabon, Nigeria, Republic of Congo, Angola, and possibly the Democratic Republic of Congo. There are two recognized subspecies, G. gorilla, western lowland gorilla, occurs in Cameroon south to the Congo River and east to the Oubangi River. Gorilla gorilla diehli, eastern lowland gorilla, is found in a small part of the Nigerian/Cameroon border in the upper drainage of the Cross River.
Biogeographic Regions: ethiopian (Native )
Wild gorillas are herbivores, subsisting mainly on juicy stemmed plants. They will also consume leaves, berries, ferns and fibrous bark. Usually gorillas feed during the morning and afternoon. Western gorillas climb trees up to 15 meters in height in search of food. Gorillas never completely strip vegetation from a single area. The rapid regrowth of the vegetation they consume allows them to stay within a reasonably confined home range for extended periods of time.
Plant Foods: leaves; wood, bark, or stems; fruit
Primary Diet: herbivore (Folivore )
The roles these animals play within their ecosystem has not been described.
Western gorillas have been used in medical study of human diseases and behavioral, linguistic, and psychological studies. The mental capacity of gorillas is still being explored. Western gorillas show more persistence and memory retention in problem solving studies than do their, more excitable, near relatives, chimpanzees (Pan). Western gorillas are more likely to perform a task out of interest than to earn a reward. After some success with chimpanzees, researchers in the mid-1970s turned their attention to communicating with gorillas using sign language, and one gorilla, Koko, mastered more than 1000 signs.
Western gorillas are also hunted illegally in Africa for their skins and their meat, which is served in restaurants of large towns. In addition, the capture and sale of gorillas for zoos, while reprehensible to many, is undoubtedly economically profitable.
Positive Impacts: food ; body parts are source of valuable material; ecotourism ; research and education
Western gorillas have been known to raid native plantations, destroying the crops and are considered a crop pest in western Africa.
Negative Impacts: crop pest
Gorillas communicate using calls, facial expressions and physical postures, and through tactile means. Scents may play some role in communication in these animals.
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
The lives of gorillas in the wild was enigmatic until American zoologist George B. Schaller observed the species for many years and published a pioneering study titled, "The Mountain Gorilla: Ecology and Behavior" (1963). American Diane Fossey followed his work by studying and living among mountain gorillas from 1963 until her death in 1985 at the Karisoke Research Center, which she had established in Rwanda in 1967.
Typically one dominant male within a gorilla troup mates with the females in that group. The dominant male, because of his superior fighting prowess and the perceived ability to better protect females and their offspring, is preferred by the females.
Mating System: polygynous
As in humans, there is no fixed breeding season for gorillas, and females menstruate every 28 days. A single young, weighing approximately 2 kg, is born after nine months of gestation. Young gorillas nurse for 3 to 4 years. Females give birth at about four-year intervals, beginning when they are approximately ten years of age. However, a high mortality rate means surviving offspring are produced only once every 6 to 8 years. Males, because of physical competition for mates, only rarely breed before the age of 15.
Breeding interval: Females give birth at about four-year intervals.
Breeding season: Gorillas breed year round.
Average number of offspring: 1.
Average gestation period: 9 months.
Range weaning age: 36 to 48 months.
Range time to independence: 3 to 4 years.
Average age at sexual or reproductive maturity (female): 10 years.
Average age at sexual or reproductive maturity (male): 15 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Average birth mass: 2061.4 g.
Average gestation period: 256 days.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 4015 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 2829 days.
Infants are suckled for 3 to 4 years. In the case of multiple young, the mother, who must carry the infants, finds it difficult to care for two and frequently allows one to die. Young grow at approximately twice the rate of human babies and are able to crawl and cling to their mother by the age of 3 months. They remain dependent upon the mother for 3 to 4 years.
Females provide the young with transportation, food, and socialization. They protect their young within the group. Males do not typically interact much with the young, although they do protect their offspring by defending the social group against potentially infanticidal males who might wish to take over control of the group.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Male, Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Protecting: Male, Female); extended period of juvenile learning
These powerful, graceful, iconic animals have attracted worldwide attention for decades. Although there was long considered be just one species of gorilla, the latest DNA evidence indicates that there are in fact two distinct gorilla species: the eastern gorilla (Gorilla beringei) and the western gorilla (Gorilla gorilla). The eastern gorilla is made up of the most famously known gorilla sub-species - the mountain gorilla (G.b. beringei), and the eastern lowland gorilla (G.b. graueri). The former occurs at the convergence of the DRC, Uganda and Rwanda, while the latter is found only in the DRC. Approximately 1000km westwards in the forests of western equatorial Africa are the western gorillas – the western lowland gorilla (G.g. gorilla), and the isolated Cross River gorilla (G.g. diehli). Some gorilla populations – particularly the mountain gorillas – are the focus of concerted conservation and restoration efforts. However, gorillas as a whole remain in danger of extinction and face a long list of severe threats, including: habitat destruction or modification by deforestation, woodland exploitation, increasing demand for arable land and energy (charcoal), infrastructure development like forest roads, viral epidemics, unstable political climates and hunting and trading in wild bushmeat. Fortunately, the United Nations Environmental Program (UNEP) has recognised the urgent need to protect these creatures and has established a Great Ape Survival Project (GRASP) with the aim of identifying the most effective conservation initiatives, and raising the funds and political support needed to achieve these initiatives.Like with any conservation effort, one of the most crucial pieces of the conservation puzzle is basic information about precisely where animals occur today. There is staggeringly little information about the whereabouts of gorillas. For more information visit the MammalMAP virtual museum or blog.
The western gorilla (Gorilla gorilla) is a great ape found in Africa, one of two species of the hominid genus Gorilla. Large and robust with males weighing around 168 kilograms (370 lb), the hair is significantly lighter in color than the eastern gorilla, Gorilla beringei, and geographically isolated from them in a region at the midwest of the African continent. Two subspecies are recognised, Gorilla gorilla diehli (Cross River gorilla) is limited to a smaller range in the north at the border of Cameroon and Nigeria. Both subspecies are listed Critically Endangered.
A formal description of the species was provided by Thomas Savage in 1847, allying the new species to an earlier description of the chimpanzee as Troglodytes gorilla in a group of eastern simians he referred to as "orangs". The author selected the specific epithet for the name given by Hanno to "wild men" he had noted on the east coast of Africa, presumed by Savage to be a species of orang.[4] The population is recognised as two subspecies:
Nearly all of the individuals of this taxon belong to the western lowland gorilla subspecies, whose population is approximately 95,000 individuals. Only 250 to 300 of the only other western gorilla subspecies, the Cross river gorilla, are thought to remain.
Western lowland gorillas are generally lighter colored than eastern gorillas. Western lowland gorillas have black, dark grey or dark brown-grey hair with a brownish forehead. Males average 167 cm (5 ft 5.7 in) although reaching a height up to 176 cm (5 ft 9.3 in), with males having an average weight of 168 kilograms (370 lb) and females weighing 58 to 72 kilograms (128 to 159 lb).[7] Captive western gorillas average 157 kg (346 lb) in males and 80 kg (176 lb) in females.[8] Another source describes the weight of wild male western lowland gorillas as 146 kg (322 lb).[9] The Cross River gorilla differs from the western lowland gorilla in both skull and tooth dimensions.
Western lowland gorillas live in groups that vary in size from two to twenty individuals. Such groups are composed of at least one male, several females and their offspring. 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 infants for the first three to four years of their lives. The interval between births, therefore, is long, which partly explains the slow population growth rates that make the western lowland gorilla so vulnerable to poaching. 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 six to eight years. Western lowland gorillas are long-lived and may survive for as long as 40 years in the wild. A group's home range may be as large as 30 km2 (12 sq mi), but is not actively defended. Wild western lowland gorillas are known to use tools.[10]
Western lowland gorillas' diets are high in fiber, including leaves, stems, fruit, piths, flowers, bark, invertebrates, and soil. The frequency of when each of these are consumed depends on the particular western lowland gorilla group and the season. Furthermore, different groups of western lowland gorillas eat differing numbers and species of plants and invertebrates, suggesting they have a food culture. Fruit comprises most of the western lowland gorillas' diets when it is abundant, directly influencing their foraging and ranging patterns. There is a correlation between the amount of time a western lowland gorilla travels and the season in which fruits are available. The western lowland gorillas spend more time traveling and feeding during the seasons when fruits are abundant compared to when there is less fruits available.[11] Fruits of the genera Tetrapleura, Chrysophyllum, Dialium, and Landolphia are favored by the western lowland gorillas. Low-quality herbs, such as leaves and woody vegetation, are only eaten when fruit is scarce. In the dry season from January to March, when fleshy fruits are few and far between, more fibrous vegetation such as the leaves and bark of the low-quality herbs Palisota and Aframomum are consumed. Of the invertebrates consumed by the western lowland gorillas, termites and ants make up the majority. Caterpillars, grubs, and larvae are also consumed in rarity.
Some ethnographic and pharmacological studies have suggested a possible medicinal value in particular foods consumed by the western lowland gorilla. The fruit and seeds of multiple Cola species are consumed. Given the low protein content, the main reason for their consumption may be the stimulating effect of the caffeine in them. Western lowland gorillas inhabiting Gabon have been observed consuming the fruit, stems, and roots of Tabernanthe iboga, which, due to the compound ibogaine in it, acts on the central nervous system, producing hallucinogenic effects. It also has effects comparable to caffeine.[12] There is also evidence for medicinal value for the seed pods of Aframomum melegueta in western lowland gorillas' diets, which seem to have some sort of cardiovascular health benefit for western lowland gorillas, and are a known part of the natural diets for many wild populations.[13]
A study published in 2007 announced the discovery of this species fighting back against possible threats from humans.[14] They "found several instances of gorillas throwing sticks and clumps of grass".[15] This is unusual, because western lowland gorillas usually flee and rarely charge when they encounter humans.
One mirror test in Gabon shows that western lowland gorilla silverbacks react aggressively when faced with a mirror, although refusing to look fully at their reflection.[16]
The World Conservation Union lists the western gorilla as critically endangered, the most severe denomination next to global extinction, on its 2007 Red List of Threatened Species. The Ebola virus might be depleting western gorilla populations to a point where their recovery might become impossible, and the virus reduced populations in protected areas by 33% from 1992 to 2007, which may be equal to a decline of 45% for a period of just 20 years spanning 1992 to 2011.[2][17] Poaching, commercial logging and civil wars in the countries that compose the western gorillas' habitat are also threats.[17] Furthermore, reproductive rates are very low, with a maximum intrinsic rate of increase of about 3% and the high levels of decline from hunting and disease-induced mortality have caused declines in population of more than 60% over the last 20 to 25 years. Rather, under the optimistic estimate scenarios, population recovery would require almost 75 years. Yet within the next thirty years, habitat loss and degradation from agriculture, timber extraction, mining and climate change will become increasingly larger threats. Thus, a population reduction of more than 80% over three generations (i.e., 66 years from 1980 to 2046) seems likely. In the 1980s, a census taken of the gorilla populations in equatorial Africa was thought to be 100,000. Researchers adjusted the figure in 2008 after years of poaching and deforestation had reduced the population to approximately 50,000.[18]
Surveys conducted by the Wildlife Conservation Society in 2006 and 2007 found around 125,000 previously unreported gorillas have been living in the swamp forests of Lake Tele Community Reserve and in neighbouring Marantaceae (dryland) forests in the Republic of the Congo. This discovery could more than double the known population of the animals, though the effect that the discovery will have on the gorillas' conservation status is currently unknown.[18][19] With the new discovery, the current population of western lowland gorillas could be around 150,000–200,000. However, the gorilla remains vulnerable to Ebola, deforestation, and poaching.[18]
Estimates on the number of Cross River gorillas remaining is 250–300 in the wild, concentrated in approximately 9-11 locations.[5] Recent genetic research[20] and field surveys suggest that there is occasional migration of individual gorillas between locations. The nearest population of western lowland gorilla is some 250 km (160 mi) away. Both loss of habitat and intense hunting for bushmeat have contributed to the decline of this subspecies. In 2007, a conservation plan for the Cross River gorilla was published, outlining the most important actions necessary to preserve this subspecies.[21] The government of Cameroon has created the Takamanda National Park on the border with Nigeria, as an attempt to protect these gorillas.[22] The park now forms part of an important trans-boundary protected area with Nigeria's Cross River National Park, safeguarding an estimated 115 gorillas—a third of the Cross River gorilla population—along with other rare species.[23] The hope is that these gorillas will be able to move between the Takamanda reserve in Cameroon over the border to Nigeria's Cross River National Park.
The names of individuals of the species includes:
The western gorilla (Gorilla gorilla) is a great ape found in Africa, one of two species of the hominid genus Gorilla. Large and robust with males weighing around 168 kilograms (370 lb), the hair is significantly lighter in color than the eastern gorilla, Gorilla beringei, and geographically isolated from them in a region at the midwest of the African continent. Two subspecies are recognised, Gorilla gorilla diehli (Cross River gorilla) is limited to a smaller range in the north at the border of Cameroon and Nigeria. Both subspecies are listed Critically Endangered.
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