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Mountain Gorillas of Uganda and Rwanda

The mountain gorillas are one of only two Eastern gorilla sub species. A small population of less than 900 individuals are dispersed in 3 African countries, occupying 4 national parks.

The critically endangered Gorilla beringei beringei – more commonly known as the mountain gorilla is found in Central Africa.

Mubare mountain gorillas

One sub species population is divided between the Mgahinga National Park, south-west Uganda; Volcanoes National Park, north-west Rwanda and the Albertine Rift montane cloud forests of the Virunga Volcanoes National Park in the eastern Democratic Republic of Congo (DRC). Here the mountain gorillas survive at an altitude of 2,200–4,300 metres (7,200–14,100 ft). The majority of the species can be found on the slopes of Karisimbi, Mikeno and Visoke – three of the dormant volcanoes. Here the very dense vegetation at the foot of the mountains gradually becomes sparser at a higher elevation. The forests can be misty, cloudy and cold.

The second populates the Bwindi Impenetrable National Park in Uganda. There’s a line of thought among primatologists that the Ugandan Bwindi population may actually be a third subspecies but, to date (and to the best of our knowledge), nothing has been finalised.

One of the biggest threats facing mountain gorillas is from the areas’ expanding population and deforestation. These fertile forests, home to the mountain gorillas are rich in biodiversity which also provides resources for the population – 85% make a living through growing food crops. With the gradual population movement towards the gorilla’s habitat, the mountain gorilla population is at risk from human diseases such pneumonia and flu.

Evolution and classification: Mountain gorillas became isolated from eastern lowland gorillas about 400,000 years ago, the two taxa separated from their western counterparts around 2 million years ago. The mountain gorilla descends from Africa’s ancestral apes and monkeys (between 24-34 million years ago). Fossil records reveal show evidence that apes were living in east Africa around 18–22 million years ago. About 9 million years ago the group of primates evolved into gorillas, it was at this time that genus Gorilla emerged. Splitting from their common ancestor with humans and chimps.

There is an unresolved debate over the mountain gorillas’ classification. First references of the genus in 1847 were as Troglodytes, later in 1852 renamed Gorilla. In 1967 Colin Groves, the taxonomist made a proposal that all gorillas be regarded as one species – Gorilla gorilla, containing three sub-species: (western lowland gorilla), Gorilla gorilla gorilla; Lowland gorillas found west of the Virungas were referred to as Gorilla gorilla graueri and mountain gorillas including, Gorilla beringei found in the Virungas and Bwindi referred to as Gorilla gorilla beringei. In 2003 The World Conservation Union (IUCN) reviewed that they should be divided into two species and Gorilla beringei and Gorilla gorilla.

Uganda mountain gorilla courtesy Chris Worden

Physical description: The mountain gorilla has a life span of between 40 – 50 years. Well adapted to living in colder habitats, the fur is longer and thicker than the fur of other gorilla species. The male weighs in at around 430 lbs (195 kg) and when standing measures 59 ins. (150 cms). The female weighs 220 lbs (100 kg) and measures 51 ins (130 cms). Gorillas have unique nose prints which are used for identification purposes making them the second largest primate species – second only to the Eastern Lowland Gorilla.

Male adults have conical shaped heads with pronounced crests to the back of the skull which anchor the temporalis muscles (these are attached to the powerful lower jaw). The female adults have less pronounced crests. The eyes are dark brown with the iris circled by a black ring. The adult male develops silver/grey hair on their backs – giving them the name ’silverbacks’ this hair is quite short in comparison to that on the remainder of their body. The mountain gorilla will climb into the branches of trees in search of fruit if the branch will hold its weight. Its arms are longer than its legs and generally knuckle walks supporting its weight with the back of its fingers.

Mountain gorillas are mainly active between 6am and 6pm. During this time they consume vast quantities of food for sustenance. They search for food in the early hours, resting around midday then forage again in the late afternoon before sleeping. During the resting period mutual grooming takes place and is important for reinforcing the social bonding within the group as well as keeping the gorillas’ hair parasite and dirt free. The youngsters will chase, wrestle and somersault, this enables them to learn how to behave and communicate within the group.

A young mountain gorilla develops twice as fast as a human baby. The female normally gives birth around the age of 10 years and will continue to produce further offspring every 4 or so years. The baby mountain gorilla weighs in at around 4 lbs, they have a human like development and the young are generally weaned then they’re about 3 years of age.

Habitat and ecology: Predominantly herbivores, the diet of the mountain gorilla consists of shoots, leaves and stems – they have access to a varied larder of 142 plants species. It’s through plants that they get most of their fluid intake so rarely need to drink. They also feeds on bark, flowers and fruit. A mountain gorilla builds itself a new nest to sleep in every day. This is made out of vegetation. Young mountain gorillas will share a nest with their mothers.

The mountain gorillas’ ‘home range’ – this refers to an area which one gorilla group utilizes for one year, determined by vegetation areas. George Schaller (mammologist, biologist and conservationist) identified ten distinct zones including bamboo forests, Hagenia forests and the senecio zone. The mountain gorilla spends most of its time in the Hagenia forests, where it consumes all parts of the galium vines: leaves, flowers, berries and stems. The gorillas will move to the bamboo forests when the fresh shoots appear in the early part of the year; then up to the subalpine regions for the giant senecio trees.

Highly sociable creatures – adult male and female mountain gorillas live within cohesive groups. The bond between a male and females is much stronger than that found between females. A silverback will be dominant for approximately 4 years, although he will be non-territorial of his area he will defend his group.

An average group has 10 individuals but can vary between 5 and 30. The dominant silverback will be the group’s leader with a subordinate silverback (normally related to the dominant male). A couple of blackback, younger males, the dominant silverback will have 3 or 4 mature females which he will be bonded to for life with their offspring – 3 to 6 infants and juveniles. Male gorillas not in a mixed group will either live alone of will be part of an all-male group, generally consisting of one older male with a few younger males.

When a male mountain gorilla reaches the age of 11 years they start to separate from the group by spending an increasing amount of time living on the edge of the group before the part entirely. They then form a group with other young males where they live for 2 to 5 years before attracting females and becoming a new group. A female will leave at about 8 years of age moving to an established group or to join an only male. It’s not uncommon for a female to join several groups before finally settling down with an adult silverback.

Fears: American zoologist, primatologist and anthropologist Dian Fossey carried our an extensive study of gorilla groups: her findings noted that the mountain gorilla had a dislike of rain, they’ll do what they can not to get wet – crossing a stream only if they can do so via fallen logs. It also appears that the young will shy away from caterpillars and chameleons and in fact have a dislike of certain reptiles.

Conservation efforts: The future of the mountain gorilla is linked to the prosperity and peace of the DRC. The welfare of the local people depends on tourism which is based around wildlife the natural resources. The International Gorilla Conservation Programme was established in 1991 with African Wildlife Foundation. They are the main International Non-Government Organization involved in conservation of mountain gorillas.

Additional notes on mountain gorillas

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