Hylobates klossii


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Hylobates klossii
Species Authority: (Miller, 1903)
Common Name(s):
English Kloss’s Gibbon, Mentawai Gibbon, Dwarf Gibbon, Kloss's Gibbon
French Siamang De Kloss
Spanish Siamang Enano

Assessment Information [top]

Red List Category & Criteria: Endangered A2cd ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Whittaker, D. & Geissmann, T.
Reviewer(s): Mittermeier, R.A. & Rylands, A.B. (Primate Red List Authority)
Listed as Endangered due to a past and continued populations decline, estimated at more that 50% over the past 45 years (approximately 3 generations) due to hunting and loss of habitat.
2000 Vulnerable
1996 Vulnerable
1994 Endangered (Groombridge 1994)
1990 Endangered (IUCN 1990)
1988 Endangered (IUCN Conservation Monitoring Centre 1988)
1986 Vulnerable (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: This species is endemic to the four Mentawai Islands (Siberut, Sipora, North Pagai and South Pagai) off the west coast of Sumatra, Indonesia (Geissmann 1995; Groves 2000; Marshall and Sugardjito 1986).
Indonesia (Sumatera)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Whittaker (2005a,b) gathered population estimates on all four Mentawai Islands, using loud-call monitoring and forested area estimates to census the animals. The species population is estimated at 20,000 to 25,000 individuals remaining on the Mentawai Islands, where they are endemic (Whittaker 2005b, 2006), which amounts to a reduction in numbers of up to 50% since the last survey in 1980 (World Wildlife Fund 1980; MacKinnon 1986, 1987). Throughout the Mentawai Islands, density averaged 12 individuals/km2 (Whittaker 2005a, b). The largest remaining population, 13,000-15,000 individuals, is found in Siberut National Park (Whittaker 2005b, 2006).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species is arboreal, diurnal, and omnivorous, though predominantly frugivorous (Whitten 1982a). Although disturbance levels in H. klossii habitat on the different islands are variable, a recent survey detected similar population densities in un-logged forests, forests logged 10 years ago, and those logged 20 years ago (Whittaker 2005; Paciulli 2004).

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).
Systems: Terrestrial

Use and Trade [top]

Use and Trade: This species is collected for the pet trade.

Threats [top]

Major Threat(s): This species is threatened mainly by hunting and commercial logging (Whittaker 2006). It is also threatened by conversion to oil palm plantations, and forest clearing and product extraction by local people (Whittaker 2006). Recently, hunting pressure has increased because of increased access to remote areas due to logging roads and tracks, as well as the replacement of bows and arrows with .177 caliber air rifles (Whittaker 2006). Also, local rituals and taboos which formerly regulated hunting have been replaced by Christianity (Whittaker 2006). The pet trade is also a threat to this species (Whittaker 2006). Although this may be a greater threat to this species than to other gibbons (D. Whittaker pers. comm.), it is rarely seen in the pet-trade in Java (Nijman 2005).

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).

Conservation Actions [top]

Conservation Actions: This species is listed on CITES Appendix I, and is protected by Indonesian law. More than half of the remaining Kloss's gibbons reside in Siberut National Park, a government protected area. Whittaker (2005b, 2006) suggested the following conservation actions: 1) increased protection for Siberut National Park, which currently lacks enforcement, 2) formal protection of the Peleonan forest in North Siberut, which is home to unusually high primate populations and is easily accessible, 3) protection of areas in the Pagai Islands by cooperating with a logging corporation that has practiced sustainable logging technique there since 1971, 4) conservation education, especially regarding hunting, and 5) the development of alternative economic models for the local people to reduce the likelihood of selling off their lands to logging companies (Whittaker 2006).

Citation: Whittaker, D. & Geissmann, T. 2008. Hylobates klossii. The IUCN Red List of Threatened Species. Version 2014.2. <>. Downloaded on 29 July 2014.
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