The siamang is the biggest of the gibbons. You can recognise it by the large black throat sac that lets it make booming calls heard several kilometres away. It is perfectly suited to life in the trees and moves by swinging arm over arm, flinging itself from branch to branch across gaps of 10 to 15 metres. It stays with one partner, defends its territory fiercely and lives in families of 2 to 6. More than half of the wild population has disappeared in 40 years, because of massive deforestation for oil palm plantations and poaching for the pet trade. The forests of Sumatra and the Malay Peninsula, where it lives, are disappearing at an alarming rate.