Of the three subspecies of gorilla, the mountain gorilla is the largest and rarest. Remarkably strong, the mountain gorilla has a short trunk and a broad chest and shoulders. Males develop a streak of silver hair on their backs when they mature and are called "silverbacks."
Male mountain gorillas reach an average of 6 feet tall (when standing upright) and weigh 400 to 500 pounds, making them the largest of the great apes (chimpanzees, orangutans, and gorillas). Females are smaller, standing an average of 4 to 5 feet tall and weighing 150 to 200 pounds.
The dense, forest ecosystems of the mountains of East Africa are the last remaining habitat of the mountain gorilla. Fewer than 650 mountain gorillas survive today in two geographically isolated populations. Approximately 320 gorillas inhabit the Virunga volcanoes region of Rwanda, Zaire, and Uganda, while the remaining number inhabits Uganda's Bwindi National Park. Gorillas live up to 53 years.
Mountain gorillas eat large amounts of vegetation and spend about 30 percent of each day foraging for food. They consume roots, leaves, stems of herbs, vines, bark from trees, shrub-sized plants, and bamboo shoots.
Mountain gorillas are shy, retiring animals. They live in social groups of 2 to 35 individuals. An adult male silverback is the leader and protector of his band, which consists of females and offspring. Silverbacks will charge anything that threatens them or their group and are known for their chest beating displays when in danger.
A silverback is an adult male gorilla, typically more than 12 years of age and named for the distinctive patch of silver hair on his back. A silverback gorilla has large canines that come with maturity. Blackbacks are sexually mature males of up to 11 years of age. Silverbacks are the strong, dominant troop leaders. Each typically leads a troop of 5 to 30 gorillas and is the center of the troop's attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites and taking responsibility for the safety and well being of the troop.
Males will slowly begin to leave their original troop when they are about 11 years old, traveling alone or with a group of other males for 2–5 years before being able to attract females to form a new group and start breeding. While infant gorillas normally stay with their mother for 3–4 years, silverbacks will care for weaned young orphans.
If challenged by a younger or even by an outsider male, a silverback will scream, beat his chest, break branches, bare his teeth, then charge forward. Sometimes a younger male in the group can take over leadership from an old male. If the leader is killed by disease, accident, fighting or poachers, the group will split up, as animals disperse to look for a new protective male. Very occasionally, a group might be taken over in its entirety by another male. There is a strong risk that the new male may kill the infants of the dead silverback.
Females reach breeding age at about 10 years old. They typically bear young every four to five years, giving birth after a gestation period of eight to nine months. Young gorillas cling to their mother's chests until they are old enough to ride on her back. A young gorilla remains with its mother until 5 years of age.
Gorillas are closely related to humans and are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language. Gorillas are known to use tools in the wild; as all of the great apes are now known to use tools.
THREATS TO GORILLAS
The eastern gorilla is listed as endangered on the IUCN Red List, with the mountain gorilla listed as Critically Endangered. The western gorilla and its subspecies are also listed as Critically Endangered. Threats to gorilla survival include habitat destruction and poaching for the bushmeat trade. The Ebola virus also threatens gorillas.
Gorillas are often victims of captivity for human entertainment. Even under the best of circumstances, captivity is cruel for gorillas. Confined to tiny cages and gawked at by crowds, animals in exhibits and acts endure constant stress. They may suffer from temperature extremes and irregular feeding and watering. Without exercise, they become listless, their immune systems are weakened, and they become prone to sickness; many resort to self-mutilation in reaction to stress or boredom. Mental illness is rampant among confined animals. Torn from their families and deprived of all dignity, every part of their lives is controlled by their captors.
Animals used in film, television, advertising or as sports mascots are ripped away from their mothers as infants. They are forced to spend most of their lives in small cages. They often live alone, resulting in severe psychological anxiety. “Performing” is stressful, confusing and often torturous. Training methods may involve beating the animals, causing them to be constantly anxious and fearful. When the animals become too large to handle, they are often dumped at shoddy roadside zoos and other substandard facilities, where they spend the rest of their lives in small, barren cages—many in solitary confinement. “Retirement” from entertainment is a long life of misery for these highly intelligent and sensitive animals. The American Humane Association’s (AHA) “No Animals Were Harmed” seal of approval is extremely misleading. AHA does not monitor living conditions of animals off set, during pre-production training, or during the premature separation of infants from their mothers.
While zoos and aquariums may appear to be educational and conservation-oriented, most are designed with the needs and desires of the visitors in mind, not the needs of the animals. Many animals in zoos and aquariums exhibit abnormal behavior as a result of being deprived of their natural environments and social structures. When the facility breeds too many animals they become "surplus" and often are sold to laboratories, traveling shows, shooting ranches, or to private individuals who may be unqualified to care for them.