Gibbons form the taxonomical family of Hylobatidae, which includes four genera: Hoolock, Hylobates, Symphalangus, and Nomascus. Gibbons are much smaller than their other ape relatives – depending on the species, adult weight ranges between 5-10 kg. They are found throughout the Indo-Malayan region, mainly in tropical, evergreen rainforests. To travel through the rainforest canopy, gibbons use a form of locomotion called brachiation, relying on their forelimbs for propulsion to swing from branch to branch.
Males and females exhibit distinct color differentiation in many species, (e.g. Nomascus and Hoolock genera) although some show significant color variation unrelated to sex (e.g. the Hylobates genus). Aside from coloration, gibbon species can be distinguished by their vocalizations; mated couples in many species sing duets to display the strength of their pair bond and mark their territories. A family group of gibbons generally consists of a monogamous adult pair and their offspring. A normal diet consists almost exclusively of fruit, but gibbons will also eat foliage and insects when fruit is scarce. Because fruit is such a prominent part of the daily diet, gibbons are important dispersers of undigested fruit seeds.
The number of gibbons of almost all species has been on decline due to habitat degradation, fragmentation and hunting. According to The IUCN Red List, four species are Critically Endangered, 13 species are Endangered, one species is Vulnerable, and the newly described Northern Yellow-cheeked Crested Gibbon and Skywalker Hoolock Gibbon are yet to be assessed.