Eastern Gorilla

These animals are very large, and live in regions where not many potential predators exist. It is not likely that they fall prey to any particular species with any regularity.

Gorillas are the largest primate, with average lengths of 150 cm for females and 185 cm for males. They are highly sexually dimorphic, with females weighing 70 to 114 kg and males averaging 160 kg. They have robust bodies, long muscular arms, short legs, massive heads, and males have large, sharp canine teeth. Mountain gorilla coats are silky and long, ranging in color from blue-black to brownish-grey. Mature males develop a large patch of silver or grey hair on their backs, giving them the name silverbacks. Males also have apocrine glands in their armpits that emit a strong odor when the animal is under stress.

Mountain gorillas differ from other gorillas in having longer hair, larger jaws and teeth, smaller nose, and shorter arms.

Range mass: 70 to 200 kg.

Range length: 150 to 185 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Gorillas can reach ages of 40 to 50 years.

Typical lifespan
Status: wild: 50 (high) years.

Mountain gorillas inhabit the montane cloud forest of the Virunga range. Occasionally they go into the afro-alpine meadows (4,000 m) where temperatures are subfreezing at night and there is little suitable food to forage on.

Range elevation: 4000 (high) m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: rainforest ; mountains

Mountain, or eastern gorillas, Gorilla beringei, are found in the Virunga volcanoes that separate the Democratic Republic of Congo from Rwanda and Uganda.

Biogeographic Regions: ethiopian (Native )

Mountain gorillas occasionally eat invertebrates, but they are primarily folivorous. They eat the roots, leaves, stems, and pith of herbs, vines, shrubs, and bamboo. Their diet is supplemented by small amounts of bark, wood, roots, flowers, fruit, fungi, epithelium stripped from roots, galls, invertebrates, and gorilla dung.

Animal Foods: insects

Plant Foods: leaves; roots and tubers; wood, bark, or stems; fruit

Other Foods: fungus; dung

Primary Diet: herbivore (Folivore )

These animals may be important in structuring plant communities, as they feed heavily on vegetation.

Gorillas may be visited by ecotourists, enhancing local economies.

Positive Impacts: body parts are source of valuable material; ecotourism ; research and education

There is continuing political pressure to convert the remaining gorilla reserves into areas for farming or commercial use. Due to the high population density, many people feel that the land would be better put to commercial use.

Mountain gorillas are highly endangered. This is due both to habitat destruction and severe poaching pressures. Gorilla species are subjected to heavy pressure from poaching for body parts and for young animals collected for zoos and private collections, generating illegal income. The civil war occurring in the region they inhabit has only added to their plight, increasing mortality through accidents and the breakdown of patrol units against poachers.

US Federal List: endangered

CITES: appendix i

IUCN Red List of Threatened Species: critically endangered

All primates have complex patterns of communication. Gorillas are known to use vocalizations to communicate with one another. Tactile communication, in the form of grooming, play, and sexual contact, also occurs. Males emit a strong odor when stressed, which appears to function as a type of chemical communication. In addition to these, gorillas use body postures and facial expressions, as well as other visual signals, to communicate with one another.

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; tactile ; acoustic ; chemical

Gorillas are usually very gentle creatures. Their only effective predators are humans. They are often thought to be "slow" or "dumb" because of their sluggishness, but in fact they are intelligent and capable of learning sign language.

There is an ongoing debate as to the relationship of gorillas, chimps and humans. Gorillas are clearly one of our closest relatives if not the closest, sharing 98% of our genome.

Mountain gorillas are polygynous; the dominant male in each group has exclusive access to all the females in the group.

Mating System: polygynous

Reproductive rates are slow and a female may leave only 2 to 6 offspring over a 40 year life-span. Males that have a harems of 3 to 4 females increase their reproductive output by fathering 10 to 20 offspring over 50 years. These animals don't mature sexually until well into their teens.

Mating behavior is initiated by the female, with a series of slow and hesitant approaches to the male. A female is receptive only during estrus, and she will cease to ovulate for several years after giving birth. The length of the estrous cycle of a female mountain gorilla is 28 days, and there is no visible external menstrual flow.

A single, dependent young is born after a eight and a half month gestation period. Weaning often doesn't occur until three years of age, and juveniles may remain with mothers for years after that. Females are sexually mature by 10 years of age, but males are unlikely to start breeding before 15 years. Reproductive output for females is about one surviving offspring every 8 years (survival implying reaching breeding age).

Breeding interval: The interval between reproductive events depends upon infant survival. Females are capable of producing an infant every 4 to 5 years.

Breeding season: These animals breed throughout the year.

Average number of offspring: 1.

Average gestation period: 8.5 months.

Range weaning age: 36 to 48 months.

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 ; fertilization ; viviparous

Females provide most of the parental care in this species. Females nurse and carry their young for about 4 years. They also play with the young, teach them, and groom them.

The role of males in parental care is less direct, although no less important. Males protect the females and the young within their social group from potentially infanticidal rival males who may take control of the group.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Protecting: Male, Female); extended period of juvenile learning

Eastern gorillas live in stable, cohesive family groups, led by a dominant silverback male. Eastern gorillas tend to have larger group sizes than their western relatives, exceptionally numbering more than 50 individuals (2). There is no distinct breeding season and females give birth only once every three to four years due to the gestation period of 8.5 months and a long period of parental care. Newborn gorillas have greyish-pink skin and can crawl after nine weeks; they are not fully weaned until 3.5 years (2). Males defend their females and offspring using their large size in intimidating displays involving charging and chest-beating (2). Eastern gorillas are herbivorous, with a heavily foliage-based diet (2). They have smaller home ranges than western gorillas as foliage is more abundant than fruit. They are diurnal but most foraging occurs in the morning and late afternoon. At night they build nests by folding over vegetation, usually on the ground (2).

The mountain gorilla occurs mainly within national parks and in some areas is protected by armed guards to prevent poaching (7). Gorillas in the Virunga region have been studied and protected for many decades and are now seen as an important source of tourist revenue (8). The United Nations Environmental Programme (UNEP) has recognised the urgent need to protect our closest relatives and has established a Great Ape Survival Project (GRASP). This project is 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). A multifaceted approach is needed to ensure the survival of one of our most impressive cousins.

The largest of the living apes, the gorilla has a characteristically heavy body shape and shaggy dark coat. 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 robust bodies with broad chests and long arms. The mountain gorilla subspecies (Gorilla beringei beringei) has a particularly long coat, which is blue-black to brownish-grey in colour. Mature male gorillas are much larger than females with a large skull crest. At about 14 years old, the hair in the saddle of their back turns white and hence they are known as 'silverbacks' (2). Gorillas are quadrupedal, walking on the knuckles of their forelimbs and the soles of their feet (2).

The eastern gorilla inhabits tropical forest. Mountain gorillas are found at altitudes between 1,160 and 4,100 metres while eastern lowland gorillas occur between 600 and 2,900 metres above sea level (5).

The best known of the eastern gorillas, the mountain gorilla, is found in two isolated populations. One is in the Virunga Volcanoes region, situated on the borders of Rwanda, Uganda and the Democratic Republic of Congo (DRC). The other occurs in Bwindi Impenetrable National Park in southwestern Uganda (1). The Virunga population was estimated to comprise 380 individuals in 2003, while there were estimated to be just 300 individuals in the Bwindi population in 2006 (1). The eastern lowland or Grauer's gorilla (G. b. graueri) is found only in eastern DRC, and is significantly more abundant than the mountain gorilla (1).

Classified as Endangered (EN) on the IUCN Red List (1), and listed on Appendix I of CITES (3).

Snares set to trap other wildlife may accidentally maim and even kill gorillas (6), while poaching for infants has re-emerged as a threat to mountain gorillas (1). The biggest threats to Grauer's gorillas result from armed conflict in and around the parks. In the past decade, many Grauer's gorillas have been shot dead in crossfire, or for food by people hiding in the forest. Ongoing instability in the region means that this problem is getting worse, as civil war has made arms more accessible and continues to create large numbers of refugees (7). A relatively new threat to the gorillas comes from the tourism. While tourism has so far aided its survival, large numbers of people coming into close contact with gorillas may put them at risk from human diseases (7).

The population structure of Mountain Gorillas shows an advancement from that of orang-utans based on the family structure. The males have bonded relationships with females and the offspring and in some cases, families combine to create small, nomadic tribes of Gorillas. Sometimes these tribes can reach 40 members. Gorillas are forced to be nomadic creatures because of their diet. They need a great deal of food, and have to travel in order to find a big enough supply to feed them all. Gorillas travel during the day and stop at night, sleeping in trees and on the ground. They create beds of mattress’ and branches and leaves for a nest. The silver back will be security watch during the night, sitting with his back against a tree, on a pile of leaves, with his powerful arms crossed over his massive chest.

The largest of all primates, the Mountain Gorilla surpasses others in strength and size. Male mountain gorillas can easily grow to be six feet tall and weigh 450 pounds. “A specimen kept for many years in the Berlin Zoo attained the record weight of 640 pounds.” The Mountain Gorilla has a huge amount of force and size as well as a ferocious appearance. The Mountain gorilla has small ears, which are different from humans. Mountain Gorillas eyes are sunk under its large brow. The head of males has a high sagittal crest to which its powerful jaw muscles are attached.” This ridge gives additional height to the skull, but that must not be taken to indicate cranial capacity, which is indeed less than that of either orang-utans or chimpanzees. The lower is as massive as that of orang-utans and the teeth are equally strong, with particulatly large fang-;ike canines. The limbs are more human in their proportions than those of orang-utans, though the arms are still considerably longer than the legs. Upright stance and, still more, and upright carriage are almost impossible. The Gorillas stands on the outer edge of its feet and the knuckles of the hand. It has nevertheless become and almost terrestrial animal. Although the females and young climb trees, they do so cautiously, but the fully grown male has become too heavy for arboreal life.”

The Mountain Gorilla is a very social animal living in cohesive groups boned together by long-term relationships between male and female gorillas. The Mountain gorilla groups are not territorial; the silverback male defends his group rather than his territory. The size of a normal gorilla group varies. Some vary from five to thirty five with an average of ten gorillas. The silverback is the dominant figure in the group, leading the group to feeding grounds, mitigating conflict within the group or outside predators, becomes the center of attention during rest sessions, and in addition, takes younger Gorillas under his wing who stay close to him and includes them in his games.

The Gorilla is found in the depths of the forests of Cameroun, Gabon and the Congo, and the Mountain Gorilla high up in the mountains north of a Lake Kivu and on the Uganda Border in the same area.

Upon its discovery, the Mountain Gorilla was thought to be very unintelligent among other anthropoids. Although the Mountain Gorilla has a small relatively small brain, it has about the mental capacity of an Orang-utan. Moutain Gorillas are slow to learn, but they can remember what they learnt. They are not as curious as the Chimpanzee and it lacks the persevereance in experiments but the mountain Gorilla is attentive. These animals evidently show greater individual variation in both character and intelligence than other anthropoids.

The more the Mountain Gorilla has been exposed to human contact; they are becoming more prone to human ailments because of the increased exposure.

The conservation status on Mountain Gorillas includes the current approximation of 786 mountain gorillas surviving in the wild. Since the discovery of the Mountain Gorilla, about 100 years ago, this subspecies of gorilla has endured uncontrolled hunting, war, disease, destruction of their forest habitat, and capture of the animal for the illegal pet trade. These unethical activities led to a dramatic decrease in the world Mountain Gorilla population to the point where extinction became a possibility. Subsequently conservation initiatives have been implemented to ensure the increase in Mountain Gorilla numbers.

Mountain Gorillas, despite their aggressive demeanor, have fears for reasons unknown to scientists. Mountain Gorillas are naturally afraid of certain reptiles. Infant Mountain Gorilla’s natural behavior is to chase anything that moves, but they have been observed to avoid chameleons and caterpillars.

At around the age of twelve, Mountain Gorillas reach sexual maturity. Although the sexual life of Gorillas is not extremely well known, they very rarely breed in captivity. Young Gorillas grow at a very rapid rate. Based off of observations made at the Berlin Zoo, the young Gorillas grew at a very rapid rate. A young male came to the zoo weighing around 33 pounds. When it died 7 years later, the Gorillas weighed 600 pounds.

The Mountain Gorilla is generally not a huge threat unless provoked. When the Male mountain gorilla is accompanied by his female, he becomes a dangerous creature. The male mountain gorilla is very aggressive will attack his intruder. However, the gorilla begins by displaying his strength and anger and sometimes is content with scaring off his attackers. In a heroic display of power, the silverback mountain gorilla will beat his breast, bark hoarsely, and finish with a huge roar.

The eastern gorilla (Gorilla beringei) is a critically endangered species of the genus Gorilla and the largest living primate. At present, the species is subdivided into two subspecies. There are 6,800 eastern lowland gorillas or Grauer’s gorillas (G. b. graueri) and 1,000 mountain gorillas (G. b. beringei). Illegal hunting threatens the species.