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Gorilla beringei (aka Mountain Gorilla)
The mountain gorilla is the largest primate in the world, with males reaching a length of 6 feet and weight of 353 pounds; females are significantly smaller, with an average length of 5 feet and weight of 198 pounds. 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 (sweat) 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.
Distribution and Habitat
There are two subspecies of eastern gorillas, the mountain gorilla (G.b. beringei) and the eastern lowland gorilla (G.b. grauen). The first is found in the Virunga Volcanoes region, situated on the borders of Rwanda, Uganda and the Democratic Republic of Congo, the other in Bwindi Impenetrable National Park in southwestern Uganda. There remain only about 5,000 eastern lowland gorillas and about 700 mountain gorillas in the wild.
The main social unit is a male with a harem of females and their offspring. These groups are nonterritorial, but severe intergroup conflicts can occur when groups encounter each other and especially if a lone male contacts the group. The dominant male of a group is massive compared to the other members and they all defer to him. Eastern gorillas tend to have larger group sizes than their western relatives, exceptionally numbering more than 50 individuals.
Females transfer from their natal group to a new group before breeding. This generally occurs at around 8 years of age. Often they join a lone male and start a new group, rather than join an established group and be a lower ranking female. Males often leave the natal group at around 11 years of age. Males, however, can't join an establish group, and they spend much time in solitary existence until they can gain females and begin a group of their own at age 15 or older.
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. Grooming often occurs between females and males, and sometimes among females.
The dominant male in each group has exclusive access to all the females in the group, but all mating behavior is initiated by the female. 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.
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 provide most of the parental care in this species, nursing and carrying 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.consisting primarily of protecting the females and the young within their social group from potentially infanticidal rival males who may take control of the group.
Females are sexually mature by 10 years of age, but males are unlikely to start breeding before 15 years. 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.
Although they will occasionally eat invertebrates, eastern gorillas are primarily folivorous. They eat the roots, leaves, stems, and pith of herbs, vines, shrubs, and bamboo, supplemented by small amounts of bark, wood, roots, flowers, fruit, fungi, epithelium stripped from roots, galls, invertebrates, and even their own dung.
Other Habits and Behaviors
Gorillas are quadrupedal, walking on the knuckles of their forelimbs and the soles of their feet.
Gorillas spend about 30% of the day feeding, 30% traveling, and 40% resting. They make nests to sleep and rest in that can be in trees, on steep slopes, or even on the ground.
Gorillas are afraid of water and will cross streams only if they can do so without getting wet (i.e. crossing over fallen logs).
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This page was last updated on August 31, 2018.