Eastern Gorilla, Gorilla beringei

The Eastern Gorilla (Gorilla beringei) is a species of the genus Gorilla and the largest living primate. Currently, the species is subdivided into two subspecies. The Eastern Lowland Gorilla (G. b. graueri) is the most populous at about 5,000 individuals. The Mountain Gorilla (G. b. beringei) has only roughly 700 individuals. Additionally, scientists are considering elevating the Bwindi Gorilla population to the rank of subspecies.

There are at least two subspecies of the Eastern Gorilla: the Mountain Gorilla (Gorilla beringei) of the volcanic slopes of Rwanda, Uganda and eastern Democratic Republic of Congo; and the Eastern Lowland Gorilla (Gorilla beringei graueri) of the lowlands of eastern Democratic Republic of Congo and Uganda. A minute population from the Bwindi Impenetrable Forest in the southern portion of Uganda and neighboring areas in Congo differs genetically from the other subspecies and, therefore, is frequently considered as a separate and undescribed subspecies.

The Eastern Lowland Gorilla and Mountain Gorilla were formerly considered to be two of three subspecies of one single species, the Gorilla (Gorilla gorilla). However, genetic research has shown that the two eastern subspecies are far more closely related than the western subspecies; the Western Lowland Gorilla (G. gorilla gorilla), which justified the separation of the classification. The two eastern subspecies are now listed as G. beringei.

The eastern gorilla is very large with a large head, broad chest, and long arms. It has a flattened nose with large nostrils. The face, hands, feet, and the breast are bald. The fur is mostly black but adult males have a silvery “saddle” featured on their backs. When the gorilla gets older, the entire fur gets grayish, much like the gray hair of elderly people. This is why the older males are occasionally referred to as silverbacks. The eastern lowland gorilla has a shorter, thicker, and deeper black colored fir while the mountain gorilla has a bluer tint. The mountain gorilla is minutely smaller and lighter than the eastern lowland gorilla, but still larger and more robust than the western lowland gorilla and the Cross River Gorilla. The males are much bigger than the females. A full-grown adult male eastern gorilla usually weighs 310-453 pounds and stands 5.6 feet upright and the females usually weigh 200-220 pounds and stands 4.9 feet tall. The tallest silverback on record was a 6.4 foot individual shot in Alimbongo, northern Kivu in May 1938. The heaviest gorilla on record was a 6 foot silverback shot in Ambam, Cameroon which weight roughly 586 pounds, although the latter area is within the range of the western gorilla, far outside the range of the eastern gorilla.

This gorilla can be seen in the lowland and mountain rainforests and subalpine forests of eastern Democratic Republic of the Congo, southwestern Uganda, and Rwanda, within the triangle between the Lualaba River, Lake Edward, and Lank Tanganyika. The eastern gorilla shows a preference for a substrate of dense plant material.

Eastern gorillas are herbivorous, with a heavy foliage-based diet. They have smaller home ranges than western gorillas as foliage is more plentiful than fruit. They are diurnal but most of the foraging occurs in the morning and the late afternoon. During the night, they built nests over the vegetation, normally on the ground.

The eastern gorillas live in stable family groups, led by a dominant silverback male gorilla. Eastern gorillas have a tendency to have larger group size than their western relatives, numbering up to 35 individuals. There isn’t a distinct breeding season and the females give birth only once every 3 to 4 years because of the long period of parental care and gestation period of 8.5 months. Newborn gorillas have greyish-pink skin and can crawl after 9 weeks of age; they aren’t fully weaned until 3.5 years old. The males defend their females and offspring utilizing their large size and intimidating displays involving charging and chest-beating.

Image Caption: Gorilla Tracking – 02. Credit: Fiver Löcker/Wikipedia (CC BY-SA 2.0)