The “Endangered Gibbons” exhibition at the great apes’ enclosure tells the story of the threat to the smaller apes. The main cause is the destruction of their natural habitat, the rainforests, with hunting and illegal animal trade also contributing. Gibbons are known for their "chants", which can last up to twenty minutes and can be often very elaborate duets between males and females. This is how they mark their territory. Each gibbon species has their own species-specific chant.
The chant of the pileated gibbon can be heard here: