Mountain gorilla

The Mountain Gorilla (Gorilla beringei beringei) is one of the two subspecies of the Eastern Gorilla. There are two populations. One is found in the Virunga volcanic mountains of Central Africa, within three National Parks: Mgahinga, in south-west Uganda; Volcanoes, in north-west Rwanda; and Virunga in the eastern Democratic Republic of Congo (DRC). The other is found in Uganda's Bwindi Impenetrable National Park. Some primatologists say that the Bwindi population in Uganda may be a separate subspecies, though no description has been finished. As of Spring 2010, the estimated total number of Mountain Gorillas worldwide is 790.

Description
The fur of the Mountain Gorilla, often thicker and longer than that of other Gorilla species, enables them to live in colder temperatures. Gorillas can be identified by nose prints unique to each individual. Males usually weigh twice as much as the females, and this subspecies is on average the largest of all gorillas. Adult males have more pronounced bony crests on the top and back of their skulls, giving their heads a more conical shape. These crests anchor the powerful masseter muscles, which attach to the lower jaw (mandible). Adult females also have these crests, but they are less pronounced. Like all gorillas they feature dark brown eyes framed by a black ring around the iris.

Adult males are called silverbacks because a saddle of gray or silver-colored hair develops on their backs with age. The hair on their backs is shorter than on most other body parts, and their arm hair is especially long. Fully erect, males reach 1.9 m (6 ft 3 in) in height, with an arm span of 2.3 m (7 ft 7 in) and weigh 220 kg (490 lb). The tallest silverback recorded was a 1.94 m (6 ft 4 in) individual shot in Alimbongo, northern Kivu in May 1938. There's an unconfirmed record of another individual, shot in 1932, that was 2.06 m (6 ft 9 in) tall. The heaviest was a 1.83 m (6 ft) silverback shot in Ambam, Cameroon which weighed about 266 kg (590 lb).

The Mountain Gorilla is primarily terrestrial and quadrupedal. However, it will climb into fruiting trees if the branches can carry its weight, and it is capable of running bipedally up to 6 m (20 ft). Like all great apes other than humans, its arms are longer than its legs. It moves by knuckle-walking (like the Common Chimpanzee, but unlike the Bonobo and both orangutan species), supporting its weight on the backs of its curved fingers rather than its palms.

The Mountain Gorilla is diurnal, most active between 6:00 a.m. and 6:00 p.m. Many of these hours are spent eating, as large quantities of food are needed to sustain its massive bulk. It forages in early morning, rests during the late morning and around midday, and in the afternoon it forages again before resting at night. Each gorilla builds a nest from surrounding vegetation to sleep in, constructing a new one every evening. Only infants sleep in the same nest as their mothers. They leave their sleeping sites when the sun rises at around 6 am, except when it is cold and overcast; then they often stay longer in their nests.

Habitat and diet
The Mountain Gorilla inhabits the Albertine Rift montane cloud forests and of the Virunga Volcanoes, ranging in altitude from 2,200–4,300 metres (7,200–14,100 ft). Most are found on the slopes of three of the dormant volcanoes: Karisimbi, Mikeno, and Visoke. The vegetation is very dense at the bottom of the mountains, becoming more sparse at higher elevations, and the forests where the Mountain Gorilla lives are often cloudy, misty and cold.

The Mountain Gorilla is primarily a herbivore; the majority of its diet is composed of the leaves, shoots and stems (85.8%) of 142 plant species. It also feeds on bark (6.9%), roots (3.3%), flowers (2.3%), and fruit (1.7%), as well as small invertebrates. (0.1%). Adult males can eat up to 34 kilograms (75 lb) of vegetation a day, while a female can eat as much as 18 kilograms (40 lb).

The home range size (the area used by one group of gorillas during one year) is influenced by availability of food sources and usually includes several vegetation zones. George Schaller identified ten distinct zones, including: the bamboo forests at 2,200–2,800 metres (7,200–9,200 ft); the Hagenia forests at 2,800–3,400 metres (9,200–11,200 ft); and the giant senecio zone at 3,400–4,300 metres (11,200–14,100 ft). The Mountain Gorilla spends most of its time in the Hagenia forests, where gallium vines are found year-round. All parts of this vine are consumed: leaves, stems, flowers, and berries. It travels to the bamboo forests during the few months of the year fresh shoots are available, and it climbs into subalpine regions to eat the soft centers of giant senecio trees.

Evolution
The evolution of the mountain gorillas is traced back to the Eocene epoch (55-34 million years ago) when the earth’s climate was fluctuating between warm and cool conditions. These early mountain gorillas were descendants of ancestral monkeys and apes found in Africa and Arabia during the start of the Oligocene epoch (34-24 million years ago). The fossil record provides evidence of the hominoid primates (apes and humans belong to this group) found in east Africa about 18-22 million years ago. The fossil record of the area where mountain gorillas live is particularly poor and so its evolutionary history is not clear. It was about 9 million years ago that the group of primates that were to evolve into gorillas split from their common ancestor with humans and chimps; this is when the genus Gorilla emerged. It is not certain what this early relative of the gorilla was, but it is traced back to the early ape Proconsul africanus. Mountain gorillas have been isolated from Eastern lowland gorillas for about 400 000 years and these two taxa separated from their western counterparts approximately 2 million years ago Gorillas have been the subject of taxonomic debate. There has been considerable and as yet unresolved debate over the classification of mountain gorillas. The genus was first referenced as Troglodytes in 1847, but renamed to Gorilla in 1852. It was not until 1967 that the taxonomist Colin Groves proposed that all gorillas be regarded as one species (Gorilla gorilla) with three sub-species Gorilla gorilla gorilla (western lowland gorilla), Gorilla gorilla graueri (lowland gorillas found west of the virungas) and Gorilla gorilla beringei (mountain gorillas including, Gorilla beringei found in the virungas and bwindi). In 2003 after a review they were divided into two species (Gorilla gorilla and Gorilla beringei) by The World Conservation Union (IUCN).