The siamang, unlike other gibbons, has an inflatable throat sac. This sac can be inflated to be as big as the siamang's head. It acts a resonatig chamber for the vcal cords, making the sounds even louder. Their hooting can be heard up to 2 miles (6.5 km) awy through the dense rain forst. 

A siamang family has a territory of abut 30-50 acres of old-growth rain forest. Each morning upon awakening a family grup of gibbons very loudly announces its presence in the forest, using a territorial hooting call and menacing gestures. This call wwarns other siamangs to stay out of their territory (and especially away frm the local fruit trees). This noisy display takes 1/2 hour or more every morning and is usually started by the adult female. The male and female have different calls. 
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