Siamangs are a large species of gibbon native to Sumatra and the Malay peninsula. They are in fact the largest gibbons, often twice the size of other species. They are always black, have two toes with a partial membrane and have large ‘gular sacs’ which they use to call loudly. They can be heard up to 2 miles away! They are endangered, being heavily affected by the pet trade. They are also strongly affected by habitat loss which has greatly reduced their numbers. The main reason for this destruction is palm oil plantations.