There are two species of gorilla found in Africa: the Western Gorilla (Gorilla gorilla) and the Eastern Gorilla (Gorilla beringei). The Eastern Gorilla consists of two subspecies: the well-known Mountain Gorilla (G. b. beringei) of Bwindi and Virunga Forests of Uganda and Rwanda and the Democratic Republic of Congo, and the Eastern Lowland Gorilla (G. b. graueri) of the eastern parts of the Democratic Republic of Congo.
Both of these subspecies are considered Endangered. The Western Gorilla also consists of two subspecies: the Western Lowland Gorilla (G. g. gorilla) principally of Congo (Brazzaville) and Gabon, and the little known Cross River Gorilla (G. g. diehli) of the border region between Cameroon and Nigeria.
Both of these subspecies are considered Critically Endangered as a result of commercial bushmeat hunting, disease epidemics and habitat loss. The very slow rate of reproduction exacerbates this situation.
It is the Western Lowland Gorilla that occurs in Odzala and is found here at the highest densities so far recorded for the species. In the area of Ngaga Camp, Western Lowland Gorillas live in groups ranging in size from 10 to 25 individuals (average 16-17 animals), usually with one silverback, 5-7 adult females and a collection of subadults, babies and sometimes subordinate males.
In this high-density area, home range size is between just less than 4 km2 and just over 8 km2 (average 5-6 km2 or 2 square miles). Their movements within the home range depend on finding food. Staple foods for example include leaves, shoots and plant material, but the seasonal availability of fruit is crucial in the diet and influences group foraging movements. Born at 2 kg (4.5 lb), female Western Lowland Gorillas can weigh around 70 kg (150lb), while the much larger males may reach 180 kg (390lb) and stand 1.8m (6 feet) in height.