Gorillas

Gorillas live only in Africa and are endangered or critically endangered depending on the subspecies.

There are two species of gorilla. One is the Western gorilla (Gorilla gorilla) and the other is the Eastern gorilla (Gorilla beringei). Each species of gorilla is subdivided into two subspecies:

Western gorilla: 
Western lowland gorilla (Gorilla gorilla gorilla).
Cross River gorilla (Gorilla gorilla diehli).

Eastern gorilla:
Eastern lowland gorilla-also known as Grauer's gorilla (Gorilla beringei graueri).
Mountain gorilla (Gorilla beringei beringei). 

Western lowland gorillas are found in central Africa, including the Central African Republic, Cameroon, Nigeria and Equatorial Guinea. The Cross River gorillas live at the Cameroon-Nigeria border near the Cross River. 

Eastern lowland gorillas are found in the mountainous forests of eastern Democratic Republic of Congo.

Mountain gorillas are found in Rwanda, Uganda and Democratic Republic of Congo within the Virunga volcanic mountains that run along the borders of these three countries. They are also found in the Bwindi Impenetrable National Park of Uganda.  

Evolutionary history

Gorillas belong to the Hominidae family that includes humans, chimpanzees, bonobos and orangutans. After chimpanzees and bonobos, gorillas are our closest evolutionary relatives having split from the human branch of the Hominidae family about 8 million years ago.

Habitat

Gorillas mainly inhabit mountainous forest, lowland tropical forest and swamp regions. Like all species of great apes they make sleeping nests out of vegetation. Western gorillas either make nests on the ground or in the trees whereas Eastern gorillas prefer to make nests on the ground.

Diet

Diet mainly consist of fruit, leaves, plant shoots, bark and flowers. They also eat insects and they have been known to break open termite mounds to feed on the larvae. Mountain gorillas regularly eat stinging nettles using complex handling strategies that reduce stinging. For instance, they fold the nettles so that the main stinging hairs are wrapped inside the centre. This makes it much easier for the gorillas to swallow the nettles. 

Social structure

Gorillas form very stable groups that are led by a dominant silverback male. The silverback will tolerate other males within the group but these tend to be his offspring that leave the group when they reach sexual maturity. The silverback’s female offspring also tend to leave the group when they reach sexual maturity.  Group size averages 10 members and it is rare for groups to exceed more than 20 members.  Groups have large home ranges that can exceed 20 square kilometres.  

Reproduction

Females usually have their first baby when they are 12 years of age.  Pregnancy lasts around 8 months and the newborn is totally dependent on its mother and clings to her underbelly. After about six months the infant will sit on the mother’s back when travelling around. Around 4 years of age the infant is weaned and the mother becomes fertile again and usually pregnant again soon afterwards.