A male mountain gorilla (Gorilla gorilla beringei), known as a 'silverback' towers over a baby gorilla in the Volcanoes National Park. 21-year-old 'Ryango' is the second-ranking male of the 9-strong Sabyinyo group whose permanent territory lies on a saddle between Mount Sabyinyo and Mount Gahinga.Sexual dimorphism is very marked with male mountain gorillas twice the size of females. A silverback (a mature gorilla of about 15 years old when the hairs on its back turn silver-grey) may weigh up to 400 lbs, with a chest the same dimension as its height (6 feet). The beautiful montane forest ecosystem of the Virunga Volcanoes is the habitat of these rare large mammals, which live in forests and glades between 9,000 and 11,000 feet. They were only discovered in 1902 when Captain Oscar von Beringe of the German Army set out to climb Mount Sabinyo, one of the seven towering volcanoes of the 44-mile-long Virunga chain straddling the borders of Uganda, Rwanda and the Democratic Republic of the Congo (DRC).