Location
As the IUCN notes, both the mountain gorilla and hill gorilla have similar populations of approximately 300 individuals each, but their locations are different. Mountain gorillas are most commonly found among the volcanoes of Virunga -- which run along Uganda, the Congo, and Rwanda: While hill gorillas also live in Uganda, they make their homes specifically inside the borders of the Bwindi Impenetrable National Park.
Habitat
The mountain gorilla makes its habitat on mountain terrain upwards of 1,500 to 4,000 meters, surrounded by dense ground vegetation and bamboo, but without much in the way of overhead cover. The hill gorilla is true to its name, because its Bwindi habitat is surrounded by hills and forest. They are also surrounded by a myriad of animals, most notably the chimpanzee. The Bwindi pairing of hill gorilla and chimpanzee habitats is the only one of its kind in Africa.
Traveling Distance and Nesting
The high altitude of its habitat directly affects the mountain gorilla's traveling and nesting habits. Compared to hill gorillas, the mountain dwellers travel less, as explained by Professor Craig B. Stanford - gorilla researcher and Chair of the University of Southern California's Department of Anthropology. Where nesting is concerned, Mountain Gorillas exclusively nest directly on the ground, while the forest habitat of the hill gorilla allows it to frequently nest in trees - most commonly the Echizogwa species.
Diet
The more adventurous lifestyle of the hill gorilla makes it more inclined to climb for its food, sometimes up to 40 meters, an action that is not common for the mountain gorilla. Professor Stanford notes that while the regular diets of the two groups include common fruits for periods of the year, the hill gorilla eats upwards of 20 percent more fruit at other times, giving it an overall diet that is more plentiful in fruit.