A primate and a great ape, the mountain gorilla is now only found in three African countries: DR Congo, Rwanda and Uganda. The mountain gorilla is critically endangered: somewhere from 700 to 900 remain. Mountain gorillas are very social creatures and they live in groups with one to two alpha males. Adult males are called silverback gorillas. The name comes from the silvery color that develops on their back as they mature and get older. The largest of all primates, mountan gorillas are larger than lowland gorillas and have longer hair and shorter arms. They are found at higher altitudes in the rocky slopes of dormant volcanoes. Mountain gorillas are diurnal and are most active during daylight hours. They are herbivores that feed on leaves, roots, tree bark and pulp. They have also been reported to eat small insects. The gestation period for females is nine months and they normally give birth to one young.