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The eastern gorilla is a subspecies of great ape that is closely related to humans, with much of the DNA structure of the two species being similar. There are two types of eastern gorillas, lowland and mountain, each named for its particular habitat in the African countries of Rwanda, Uganda and the Democratic Republic of Congo. The lowland and mountain gorillas are both classified as endangered species.
Both subspecies of the eastern gorilla are among the largest of all apes. Adult male eastern lowlands, also known as Grauer's gorillas, can grow up to 69 inches (175 cm) tall and weigh as much as 360 pounds (165 kg). Mountain gorilla males may be slightly larger, standing up to 70 inches (177 cm) tall and weighing up to 440 pounds (200 kg). The females of both subspecies tend to be approximately half the size of the males. Their arm spans, the measurement from the fingertips of one hand across the body to the fingertips of the other hand, can be greater than seven feet (2.13 m).
Gorillas are typically active in the daytime and sleep at night, as most humans do. The eastern gorilla is an herbivore and spends most of the day eating plant materia,l such as leaves, shoots and vines. Eastern lowland gorillas also eat fruit, which they must often travel to find, making their home areas larger than those of the mountain gorilla.
The eastern gorilla lives in a pack with anywhere from five to 30 members, including a dominant male often called a "silverback" due to the color the hairs on his back turn as he ages. Other pack members include adult females, offspring and often several submissive males, or blackbacks, as well. Only the silverback may mate with the group's females, creating offspring with a gestation period of eight and a half months followed by approximately three years of nursing. Many gorilla babies do not survive their first three years of life, with an infant that will reach maturity born only once every six to eight years, furthering the population decline.
Along with infant mortality, other factors have led the eastern gorilla to become an endangered species. Loss of habitat due to clearing of the forests for farming, conflicts in the region in recent years, and poaching have left the eastern lowlands gorilla species numbering less than 5,000, while there are fewer than 800 mountain gorillas in existence today. The mountain gorilla, made famous by the work of primatologist Dian Fossey, also has suffered population losses due to diseases brought into its habitat by increasing numbers of human visitors.