Gorillas typically live in the lowland tropical rainforests of Central Africa, although some subspecies are found in montane rainforest (between 1,500 and 3,500 meters) and in bamboo forest (between 2,500 to 3,000 meters).
Gorillas have a well-developed social structure, forming stable family groups in which the dominant male keeps his position for years.
Group size is usually 5-10 individuals, but can vary from 2 to over 50 members. According to group size, habitat quality and food availability, a group's home range may vary from 5 to over 30km², with frequent overlap between group ranges.
If a male leaves a group, he wanders alone for a number of years, then sometimes establishes a range next to or overlapping that of his old group.
Adult males that stay in a group are generally the offspring of the dominant male and eventually will take over leadership.
As a general rule, female gorillas leave their group at maturity to join other groups or single males, although cases of females reproducing in their original groups are known.
Females become sexually mature at 7-8 years old, but do not start to breed until several years later. Males mature later than females, with few breeding before the age of 15 years.
High infant mortality, a long gestation (8.5 months), a tendency to single births, and a prolonged period of maternal care mean that, on average, only one baby is reared in a 4-6 year period. Females generally give birth to only three or four surviving young during their reproductive life.
The mortality rate for gorillas less than one year old is high, but for adults the rate is only 5%. In the wild, they might live to be 40 years old. In the United States, a captive gorilla was reported to have lived to the age of 54.
Gorillas are mainly herbivorous (vegetarian) and spend almost half of the day feeding on stems, bamboo shoots, and a variety of fruits, supplemented with bark and invertebrates.
At some sites, western lowland gorillas have been known to break open termite nests and feed on the larvae.