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Mountain Gorillas

Gorillas are the largest living primates and are widespread residents of the equatorial African rainforest with a global population of around 100,000 majorly in the Congo basin. Until 2001, all gorillas were assigned to the species Gorilla gorilla, split into three races: the western lowland gorilla (G.g gorilla) of the western Congo Basin; the eastern lowland gorilla(G. g. graueri) in the eastern DRC; and the mountain gorilla(G. g. beringei), which lives in highland forest on the eastern side of the Albertine rift.

Whereas the Western race was formally described in 1847, the mountain gorilla remained unknown to zoologists until 1903 when the German army officer Captain Von Beringe shot the first two documented individuals on the slopes of Mount Sabinyo. The eastern lowland gorilla remained described later in 1914.

The post-millennial advances in DNA testing and fresh morphological studies have forced the revision of this conventional taxonomic classification. It seems that the western and eastern populations, whose ranges lie more than 1,000km apart, diverged at least 250,000 years ago and should be treated as two species, usually referred to as the western gorilla (G.gorilla) and the eastern gorilla (G. beringei).

The status of the other western race (G.g.gorilla) is relatively secure, with a global population estimated at 80,000-90,000 spanning half a dozen countries. Furthermore, the Cross River race G.g.dielhi is IUCN-listed as “Critically Endangered” since it lives in five fragmented populationsin the Cameroon-Nigeria Border region, with a combined total of fewer than 300 individuals, making it one of the world’s most threatened primate taxa. Elsewhere numbers of western gorilla are still in decline, largely due to hunting for bush meat and the lethal Ebola Virus.

Mountain Gorillas in the Virungas

The fate of the eastern gorilla-still split into lowland and mountain race-is more precarious still. As recently as the mid 1990s, an estimated of 17,000 eastern lowland gorillas remained in the wild, but it is though that the population has since dropped below 5,000 largely as a result of the ongoing civil war in the DRC. Rarer still but more numerically stable, is the mountain gorilla with a global population of fewer than 900 individuals split between the border-straddling Virunga Volcanoes and Uganda’s Bwindi Impenetrable National Park.

The first study of Mountain Gorilla Behavior

George Schaller undertook the first study of mountain gorilla behavior in the 1950s. His work laid a foundation for the better publicized research initiated by Dian Fossey in the 1960s. The brutal –and still unsolved murder of Fossey at her Rwandan research center in December 1985 is generally thought to have been the handiwork of one of the many poachers with whom she crossed swords in the Virungas. Fossey’s acclaimed book Gorillas in the Mist remains perhaps the accessible starting point for anybody who wants to know more about mountain gorilla behavior, while the eponymous movie, a posthumous account of Fossey’s life, drew global attention to the plight of mountain gorilla.

The Mountain gorilla is distinguished from its lowland counterparts by several adaptations to its high-altitude home, most visibly a longer and more luxuriant coat. It is on average bulkier than other races, with the heaviest individual gorilla on record (of any race) being Guhondo, the 220kg dominant Silverbackin Rwanda’s Sabinyo group.

The life of a Mountain Gorilla

The mountain gorilla is a highly sociable creature, living in defined groups of anything from 5 to 50 animals. A group typically consists of one dorminant Silverback male( the male’s back turns silver when he reaches sexual maturity about 13years old) and sometimes one or more surbodinate animals. Unusually for mammals, it is the male who forms the focal point of  gorilla society; when a silverback dies, his troop disintegrates. A Silverback will start to aquire his harem at about 15years of age, most normally by attracting a young sexually mature female from another troop. He may continue to lead a troop into his 40s.

A female gorilla reaches sexual maturity at the age of eight, after which she will often move between different troops several times. Once a female has successfully given birth, however, she normally stays loyal to the same silverback until he dies, and she will even help defend him against other males. (when a male takes over a troop, he generally kills all nursing infants to bring the mothers into oestrus more quickly, a strong motive for the female to help preserve the status quo.) A female gorilla has the same gestation period similar to that of a human, and if she reaches old age she will typically have raised upto six offspring to sexual maturity. A female’s status within the troop is based on the time she has been with the Silverback: the alpha female is the longest serving member of the harem.

The mountain gorilla is primarily vegetarian. Its dietary mainstay is bamboo shoots, but it has been recorded eating leaves, shoots, stems or other parts of more than 140 different plant species. About 2% of its diet is made up of insects and other invertabrates, with ants being the most favoured protein supplement. A gorilla troop will spend most of its waking hours on the ground, but climbs into the trees at night, when each group member builds its own temporary nest. Gorillas are surprisingly sedentary creatures, typically moving less than 1km a day,  which makes tracking them on a day-to-day basis relatively easy for experienced guides. A group will generally only move a long distance after a stressful incident for instance an aggressive encounter with other gorillas. But this is quite rare, as gorillas are fundamentally peaceable animals. They have few enemies and often live upto 50years in the wild, but their longterm survival is threatened by poaching, deforestation and exposure to human-borne-diseases.

Races of Mountain Gorillas in the Virungas

It was previously thought that the Virunga and Bwindi gorilla populations were racially identical, not an unreasoanable assumption given that a corridor of mid-altitude forest linked the two mountain ranges until about 500years ago. But recent DNA tests shows sufficient genetic differences to suggest that the two breeding populations have been have been mutually isolated for many millennia. Based on this, some taxonomists now propose the ‘mountain gorilla’ be split into discrete Bwindi and Virunga races, the former endemic to Uganda, Rwanda and the DRC. Neither of these proposed races numbers more than 500 in the wild, nor have they ever bred successfully in captivity, and both meet several criteria for an IUCN classification of ‘critically Endangered’

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