thumb|Kloss's gibbon
thumb|The Mentawai Islands
Kloss's gibbon (Hylobates klossii), also known as the Mentawai gibbon, the bilou or dwarf siamang, is an endangered primate in the gibbon family, Hylobatidae. It is identifiable in that it is all black, resembling the siamang with its black fur, but is considerably smaller and lacks the siamang's distinctive throat pouch. Kloss's gibbon reaches a size and weigh at most . As is the case for all gibbons, they have long arms and no tail. Males and females are difficult to distinguish. These islands are hearths of biodiversity, and are the homes of many endemic species. Like all species of gibbons it lives together in pairs that stake out a territory from approximately of size. This area is defended vehemently against other gibbons. Its diet consists mainly of fruits, occasionally also eating different plant parts, bird eggs, insects and small vertebrates.
Communication
Kloss's gibbon are unique gibbons because the two sexes do not vocalize songs in unison. Male Kloss's gibbon sing before the sun rises and female Kloss's gibbon vocalize songs once the sun has risen. The calls emitted by the females could offer other members of the species information about their position in the canopy. Territories are often contested and Kloss's gibbons defend their territories with aggression and threats. Kloss's gibbons diet consists of fruit, leaves, shoots, and insects. Unhabituated Kloss's gibbons sometimes exhibit a warning behavior in which they act as a lure toward people. There are several threats that pose significant risk to Kloss's gibbon. Kloss's gibbon has no natural predators, and humans are the main threat to the existence of this primate. Road development and the adoption of air rifles are allowing natives to kill Kloss's gibbon easier and at higher rates.