Siamangs swing through the trees with the greatest of ease! How do they do it? First of all, their arms are much longer than their legs—some can have an armspan of almost 5 feet wide. Also, their thumb and big toe are opposable, making it easy for them to grasp branches. Sometimes, instead of swinging, siamangs walk along tree limbs, holding their arms out to the side to help them balance.
Siamangs sleep sitting upright on branches. When they wake up early in the morning, they “sing.” The siamang’s “song” includes very loud booms and barks. Siamangs have a special throat sac that blows up like a balloon. The inflated sac makes their calls even louder. The calls they make warn other siamangs that this territory is taken. Pairs of males and females also sing together, making a special song all their own!