That the siamang (Symphalangus syndactylus), the largest of the gibbons, is an arboreal species is shown in this video. To make themselves better heard they first travel to the top of the trees in their enclosure as they would do in their native habitat, the forests of Malaysia, Thailand, and Sumatra. The siamang is distinctive for two reasons. The first is that two digits on each foot are partially joined by a membrane – hence the name “syndactylus”, from the Ancient Greek “sun” (=united) + “daktulos” (=finger). The second is the large gular sac (found in both males and females of the species), which is a throat pouch that can be inflated to the size of the siamang’s head, allowing it to make loud, resonating calls or songs. The amplified call can be heard over several kilometres. The second feature is clearly audible in this footage, and you can see the gular sac too.