Hylobates klossii
Kloss's gibbon

Kloss' gibbons, Hylobates klossi, are found in Siberut, Sipura, North Pagai, and South Pagai in the Mentawai Islands, western Sumatra, and Indonesia. (Haimoff and Tilson, 1985; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

Kloss' gibbons can be found in the upper canopy of semi deciduous monsoon forests and tropical evergreen forests. (Haimoff and Tilson, 1985; "Kloss' gibbon (Hylobates klossii)", 2002)

Hylobates klossii has long forearms for brachiation. These tail-less, slender primates have dense, glossy, black hair with buttock pads and a large throat sac located under the chin. The throat sac helps to enhance their calls. Females are slightly larger than males, with males weighing about 5.6 kg and females weighing about 5.9 kg. Head and body length ranges from 440 mm to 635 mm. (Chivers and MacDonald, 2001; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

Kloss' gibbons are monogamous. Mated pairs of males and females, with their young, form the basic social unit. (Haimoff and Tilson, 1985; "Kloss' gibbon (Hylobates klossii)", 2002)

The gestation period of H. klossii lasts 7 to 8 months, with one infant born every 2 to 3 years. Weaning occurs early in the second year of life. Kloss' gibbons reach sexual maturity at 6 to 7 years of age. Young do not usually disperse from their family unit until they reach late adolescence. The testicular sac in males is covered by short, sparse hairs. In females, the labia majora is prominent, making it difficult to distinguish males from females in the field. (Chivers and MacDonald, 2001; Parker, 1990; Whitten, 1982)

Males and females participate in caring for the young. Around the time of adolescence, males and females will disperse from their parent's group. Often parents will assist dispersing adolescents in obtaining territory by accompanying the young into new territory and threatening those occupying the new area. (Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

The lifespan of Kloss' gibbons may be as long as 25 years. Other members of the genus Hylobates are known to live upwards of 44 years in captivity. (Parker, 1990)

Hylobates klossii is an arboreal species that moves from tree to tree by brachiation. Often these trees are at least 10 meters apart. This causes them to have moments where they are moving through the air not supported by any trees, almost as if they are flying. If on the ground, they can move bipedally for very short distances. They move an average of 1,514 meters per day and are diurnal, sleeping in trees at night. They often they use the same trees each night for sleeping. They are active up to 10 hours per day.

Kloss' gibbons are territorial, with adolescents and sub-adult males cooperating with their father to protect the group's territory. (Chivers and MacDonald, 2001; Haimoff and Tilson, 1985; Massicot, 2002; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

Mated pairs occupy a small home range of about 20 to 35 hectares, of which they defend about 10 hectares from up to 6 other groups that occupy the surrounding square kilometer. (Chivers and MacDonald, 2001; Haimoff and Tilson, 1985; Massicot, 2002; Nowak, 1999; "Kloss' gibbon (Hylobates klossii)", 2002)

Kloss' gibbons are known for their magnificent vocal communication. Females tend to have the most distinctive calls with a slow rise and fall, interrupted by a trill sequence. Male calls consist of moans and "quiver-hoots". Males will sing solos from 10 minutes up to 2 hours in both the pre- and post-dawn hours. Often, breeding pairs form duets together 2 to 3 hours after dawn, with the female's contribution lasting about 15 minutes. Occasionally, the young will join in the duet of their parents. It has been hypothesized that the duets are a means of intimidating neighbors to defend their territory and/or as a way to maintain social organization. Studies have shown that both males and females can be identified by the individuality of their calls, with each animal having its own unique voice. (Cowlishaw and MacDonald, 2001; Haimoff and Tilson, 1985; Massicot, 2002; Nowak, 1999)

Kloss' gibbons also use chemical, tactile, and visual modes of communication. Social grooming is an important form of social bonding and facial and body gestures are important ways of communicating among gibbons. Another important interaction is play behavior centered on the infant. ("Kloss' gibbon (Hylobates klossii)", 2002)

Kloss' gibbons are primarily frugivorous, preferring to eat fruits with high sugar content, such as figs, 72 percent of the time. They will also consume flowers, eggs, small vertebrates, and insects 25 percent of the time. This species tends to spend time apart from members of its own group while feeding -- up to 50 meters at times. In the wild, Kloss' gibbons have been observed to spend a large amount of feeding time searching for arthropods. (Massicot, 2002; Nowak, 1999; Whitten, 1982; "Kloss' gibbon (Hylobates klossii)", 2002)

Predators of Kloss' gibbons include leopards, snakes, and large birds of prey. Their social system means that many individuals are vigilant and will warn other members of the troup of impending danger. (Massicot, 2002; Nowak, 1999; Whitten, 1982)

Kloss' gibbons act as important seed dispersers in their forest ecosystems.

Kloss' gibbons are a potential source of ecotourism dollars, as well as being important parts of a healthy ecosystem from which humans benefit.

There are no known negative impacts of Kloss' gibbons.

The IUCN lists H. klossii as vulnerable due to the extent of occurrence and/or quality of habitat. The status of H. klossii is threatened because of an increased human population, hunting, and deforestation. CITES lists H. klossii on their Appendix I list. ("IUCN Red List of Threatened Species", 2002; "The CITES Appendices I, II, and III", 2002; Massicot, 2002; Nowak, 1999)

Hylobates means "dweller in the trees". (Nowak, 1999)