Siamang

The throat sac

The siamang’s most distinctive feature is its large, naked, grey throat sac — a resonating chamber that inflates to the size of a grapefruit before each call. The sac allows the siamang to produce calls of extraordinary volume: up to 110 decibels, among the loudest vocalisations of any land animal relative to body size. Calls carry through dense rainforest for several kilometres.

Duetting pairs

Siamangs are monogamous and mate for life. Established pairs sing coordinated morning duets that serve as territorial declarations and pair-bond reinforcement. The male and female have distinct call sequences that interlock in elaborate patterns built up over years of practice. Young siamangs learn their parents’ call patterns and must develop their own with a future partner.

Forest canopy life

Siamangs are brachiators — they swing through the canopy using their long arms with great speed and efficiency, rarely descending to the ground. Their arms span up to 1.5 metres. Two toes on each foot are partially fused (giving the genus its name, syndactylus meaning fused-toed), which helps with gripping branches. They eat mainly leaves and fruit, supplemented by flowers.

Rainforest loss

Siamang populations have declined sharply due to deforestation for palm oil and paper pulp plantations. They require tall, intact primary forest and cannot survive in fragmented or degraded habitat. They are also taken for the illegal pet trade, with adults killed so infants can be captured.