Mountain gorillas live in groups that usually include a single mature male, two to four adult females and two to five immature animals (less than eight years old). Lone males are the only individuals living outside these groups. Aggression in gorillas is extremely rare and serious fights occur only when a group leader meets another group leader.

     Females begin breeding at about 10 years of age, but males do not breed until they are at least 15 years. As a result of strong male-male competition, very few males have the opportunity to breed before 15-20 years of age. The gestation period is about 8.5 months, and usually only a single young is born. Offspring weigh 1.8-3.2 kg when first born, and their grayish-pink skin is sparsely covered with fur. They begin to crawl at about nine weeks and can walk from 30-40 weeks. Gorillas are weaned at 2.5-3 years of age. Females successfully produce offspring only once every four to eight years, since 40-60% of offspring die in their first year of life.

     Western Lowland Gorillas are found in Western Africa. Reports list there remain only 10,000-35,000 western lowland gorillas in the wild. It is this subspecies most frequently seen in captivity.  The western lowland gorilla is found in south-east Nigeria, Cameroon, Equatorial Guinea, Gabon, Congo (Brazzaville), and the Central African Republic.

    Eastern Lowland Gorillas are found in Eastern Zaire.  Currently there are approx. 4,000 free-living. Less than 24 in captivity.