Kloss' gibbons, Hylobates klossi, are found in Siberut, Sipura, North Pagai, and South Pagai in the Mentawai Islands, western Sumatra, and Indonesia.
Biogeographic Regions: oriental (Native )
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.
Average mass: 5.7 kg.
Range length: 440 to 635 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: female larger
Average mass: 5900 g.
Catalog Number: USNM 121678
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Male; Adult
Preparation: Skin; Skull; Partial Skeleton
Collector(s): W. Abbott
Year Collected: 1902
Locality: South Pagi Island [= Pulau Pagai Selatan], Sikakap Strait [= Selat Sikakap], Sumatra, Sumatera Barat, Indonesia, Asia
Kloss' gibbons can be found in the upper canopy of semi deciduous monsoon forests and tropical evergreen forests.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: rainforest
Habitat and Ecology
Gibbons in the Siberut area studied by both Tenaza (1974, 1975) and Tilson (1980) had unusually small average home ranges of 7-11 ha. A gibbon group studied in a different area on Siberut had a home range size of 32 ha, similar to that in other species of the genus Hylobates (Whitten 1980, 1982b).
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.
Animal Foods: birds; mammals; amphibians; reptiles; eggs; insects
Plant Foods: leaves; fruit; flowers
Primary Diet: herbivore (Frugivore )
Kloss' gibbons act as important seed dispersers in their forest ecosystems.
Ecosystem Impact: disperses seeds
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.
- leopards (Panthera pardus)
- large snakes (Serpentes)
- large birds of prey (Falconiformes)
This list may not be complete but is based on published studies.
Known prey organisms
This list may not be complete but is based on published studies.
Life History and Behavior
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.
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.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: duets ; choruses
Perception Channels: visual ; tactile ; acoustic ; chemical
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.
Status: wild: 25 (high) years.
Status: captivity: 37 (high) years.
Lifespan, longevity, and ageing
Kloss' gibbons are monogamous. Mated pairs of males and females, with their young, form the basic social unit.
Mating System: monogamous
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.
Breeding interval: One infant is born every 2 to 3 years to an individual female.
Breeding season: These animals breed throughout the year.
Average number of offspring: 1.
Range gestation period: 7 to 8 months.
Range weaning age: 24 (high) months.
Range age at sexual or reproductive maturity (female): 6 to 7 years.
Range age at sexual or reproductive maturity (male): 6 to 7 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Average number of offspring: 1.
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.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Provisioning: Female, Protecting: Male, Female); post-independence association with parents; extended period of juvenile learning
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.
US Federal List: no special status
CITES: appendix i
IUCN Red List of Threatened Species: endangered
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1994Endangered(Groombridge 1994)
- 1990Endangered(IUCN 1990)
- 1988Endangered(IUCN Conservation Monitoring Centre 1988)
- 1986Vulnerable(IUCN Conservation Monitoring Centre 1986)
The extent of the threats from logging, hunting, and the pet trade faced by this species varies depending on location. The very large population in Siberut National Park, on central Siberut, lives in a protected area but is subject to moderate hunting pressure from local people. In the Peleonan forest, northern Siberut, the habitat was logged 20 years prior but faces low hunting pressure. This area is significant because four of the endemic Mentawai primates (H. klossii, Simias concolor, Presbytis potenziani and Macaca siberu) exist here in high densities. Populations in Saureinu, Sipora are subject to traditional use by locals but limited logging. In South Pagai, forest plots are selectively logged but there is high hunting pressure. Animals on North Pagai were not censused, but logging and hunting occurs there as well (Whittaker 2005b).
Relevance to Humans and Ecosystems
There are no known negative impacts of Kloss' gibbons.
Kloss' gibbons are a potential source of ecotourism dollars, as well as being important parts of a healthy ecosystem from which humans benefit.
Kloss's gibbon (Hylobates klossii), also known as the Mentawai gibbon or the bilou, is a 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 44 to 63 cm and weigh at most 6 kg. As is the case for all gibbons, they have long arms and no tail.
Kloss's gibbon exclusively lives on the Mentawai Islands that lie to the west of Sumatra. It is a diurnal inhabitant of the rain forest that hangs in the trees from its long arms and rarely comes to the ground. Like all species of gibbons it lives together in pairs that stake out a territory from approximately 20 to 30 hectares 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.
The singing of the female Kloss's gibbon is considered the most beautiful of all the gibbons' songs. Unlike most other gibbon species (except for the Javan silvery gibbon, Hylobates moloch), Kloss's gibbon males and females do not sing duets. Males typically sing in the hour before sunrise, while an all-female chorus occurs after sunrise. The singing of the gibbons serves to warn off other animals from their territory, and possibly to strengthen the family bonds.
The reproductive cycle of Kloss's gibbon is similar to that of other gibbons. Every two to three years the female may give birth to a single young (with a gestation period of seven months). The young is weaned in the middle of its second year, and is fully mature in about seven years. Their life expectancy is about 25 years in the wild, and up to 40 years in captivity.
- Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M, eds. Mammal Species of the World (3rd ed.). Baltimore: Johns Hopkins University Press. p. 179. OCLC 62265494. ISBN 0-801-88221-4.
- Whittaker, D. & Geissmann, T. (2008). Hylobates klossii. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
- Kloss Gibbon at the zoo
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