The gorillas, previously considered a single species, were recently divided into two species and five subspecies. The mountain, Bwindi and Cross River gorilla populations all number only in the hundreds and are considered critically endangered. It is this subspecies most frequently seen in captivity and mounted in museum collections. The Virunga population were the subjects of Dian Fossey's field study. Only about 325 mountain gorillas remain in the wild.
None is in captivity.
The Cross River gorilla is a good example of why we must be very careful not to neglect possible diversity. The distribution of gorillas in Africa is discontinuous. Terrestrial vs. Arboreal Gorillas are mainly ground-living, but where trees are strong enough and fruiting, whole groups can be seen up them, even the mature males. The height above the ground that animals build the nests in which they sleep at night is inversely proportional to their weight, with the silverbacks usually being on or close to the ground. Gorilla and chimpanzee nests look alike, but can usually be told apart because chimpanzees nest so much higher up trees than do gorillas.