The mountain gorilla can be found in the central African countries of Rwanda, Congo, and Uganda. They make their habitat in tropical forests in the mountains, and live in troops consisting of one male and several females. The mountain gorilla has a robust body and protruding stomach, and moves on the ground by “knuckle-walking” as its arms are longer than its legs. When a male reaches maturity, its back becomes a grayish-white color, and its head takes on a conical shape. It also begins to use chest-beating as a way of expressing aggression. Mountain gorillas eat thistles and nettles that grow in the mountains. It is estimated that as little as 1,000 gorillas currently exist in the wild, making them at high risk of extinction.