Gorillas are great apes that belong to the genus Gorilla. The gorilla is the largest living primate.

Gorillas have fur that is black or brownish gray. Some gorillas have red fur on their heads. When a male reaches sexual maturity, a patch of light gray hair grows on his back. Older males, therefore, are known as "silverbacks".

There is no hair on the face, ears, hands or feet are of a gorilla. A gorilla's skin is black.

Gorillas are stocky animals. Adult female gorillas weigh between 150 and 250 pounds (65 and 115 kilograms) and are  about 5 feet tall  (150 centimeters) on average when standing upright.

Male are much larger than females.  Adult males average about 5 ½ feet (170 centimeters) tall and weigh between 300 and 500 pounds (135 and 230 kilograms).

Gorillas have prominent brow ridges. Their eyes and ears are small. They have short muzzles with large nostrils. A male gorilla has large canine teeth.

A gorilla's hands are large. The arms are long. The upper arms are very short compared to the forearms.  Gorillas have short legs.

Gorillas usually walk on the ground, although they can climb trees. They are knuckle walkers - they walk on all fours with their wrists flexed, so that they place their weight on their knuckles and the soles of their feet.  Having long arms and short legs is conducive to knuckle walking.

However, gorillas can also walk upright on their hind legs.

Lighter gorillas can swing from tree to tree, a method of locomotion known as brachiation

Gorillas are foragers. The diet of a gorilla includes fruits, leaves, flowers, tubers, fungi and insects. Gorillas usually get all their water from plants that that they eat, but they have been observed drinking at times.

At night, gorillas sleep in nests in low trees or on the ground. They make their nests out of plants. They also nap in nests the middle of the day.

Gorillas have been seen using tools in the wild. In 2005, a female gorilla was reported using a stick to check how deep a swamp was, and another was seen making a bridge out of a detached tree trunk. Gorillas in captivity use tools to get food.

Social Organization

Like other primates, gorillas have a complex social structure. Gorillas live in social groups, known as troops, which can have between 3 and 50 individuals. A typical troop will contain one silverback, who is the group's leader and protector, a younger male who has not yet reached sexual maturity, several adult females and their children.

The troop will travel from place to place together, looking for food.

All of the adult females will mate with the silverback.

Males in the troop will defend the females and the children.

When a young male gorilla reaches sexual maturity, he will usually leave the troop and form his own troop. He may also stay in the troop and remain subordinate to the dominant silverback or join a troop consisting of other mature males.

Sometimes, a male will take over another troop and kill the babies in the troop so the females will mate with him. (Females will not mate while they are nursing.)

A male that has been displaced from his troop by another male will often lead a solitary existence afterwards.

If troops in the same region are led by related males - brothers, for example - peace between them is very likely.

In general, gorillas are peaceful animals. Troops often have overlapping territories.

After reaching maturity, a female will move to another troop if there are no males in her group with whom she can mate - particularly if the only male in the troop is her father.  Sometime, females move from troop to troop.

A newly mature female may join a solitary male, and they will form their own new troop together.

If the silverback dies, a younger male may take over, or the rest of the troop may break up. Sometimes, the females will stay together until another male joins them and takes over.

Lifecycle

In the wild, gorillas reach sexual maturity between the ages of 10 and 13. Females in captivity reach maturity earlier. Like humans, gorillas don't have a breeding season and, also like humans, female gorillas menstruate around every 28 days.

The gestation period of a gorilla is around 8 1/2 months.

A gorilla will usually have one baby at a time. Sometimes, a gorilla will give birth to twins.  If she does, she may neglect one of the babies, and it will die.

Gorilla babies are nursed for three or four years.  A female gorilla will not have another child until she finishes nursing.

Gorillas in the wild usually live to be between 30 and 40 years old.  Life expectancy may extend to 50 years in captivity.

Gorilla Communication

Gorillas living in the wild communicate by vocalizing.  Different sounds have different meanings. Scientists have identified more than 20 distinct gorilla sounds.

Gorillas also communicate with facial expressions and body language.

When a male encounters a rival male, he will hoot and beat his chest in a show of dominance.

Touching is also an important method of gorilla communication, used during play, grooming and sex.

Koko and Michael, two captive gorillas, were taught to use sign language to communicate with humans.

Gorilla Species

Scientists have identified two living gorilla species: the western gorilla (Gorilla gorilla) and the eastern gorilla (Gorilla beringei).

Western Gorilla

The western gorilla tends to have grayer fur than the eastern gorilla.  Western gorillas are often redheads.

The western gorilla is divided into two known subspecies: the western lowland gorilla (Gorilla gorilla gorilla) and the Cross River gorilla (Gorilla gorilla diehli).

Western lowland gorillas live in forests in western equatorial Africa, in Nigeria, Gabon, Cameroon, Congo, the Democratic Republic of the Congo, Angola, Equatorial Guinea and the Central African Republic.

Most of what we know about gorillas comes from studying western lowland gorillas, as this is the most common gorilla subspecies.

Cross River gorillas can be found in a small 4,600 square mile (12,000 square kilometer) region around the Cross River, which runs along the border between Cameroon and Nigeria.

Eastern Gorilla

There are two known species of eastern gorilla: the eastern mountain gorilla (Gorilla beringei beringei) and the eastern lowland gorilla (Gorilla beringei graueri).

The eastern mountain gorilla lives in a small region in the rain forests of the Virunga Mountains, a volcanic mountain chain in Uganda, Rwanda and the Democratic Republic of Congo.

Eastern mountain gorillas have longer fur, smaller noses and larger teeth and jaws than other gorillas.

The eastern lowland gorilla can be found in the wild only in a region in the eastern part of the Democratic Republic of Congo.

Eastern mountain gorillas are endangered.  All other gorilla subspecies are critically endangered.  Gorillas have been victims of habitat loss as well as human hunters.