Hylobates agilis

Taxonomy (Name)

Picture

Distribution, Range

This species is found in Sumatra (Indonesia) (southeast of Lake Toba and the Singkil River), Peninsular Malaysia (from the Mudah and Thepha Rivers in the north to the Perak and Kelanton Rivers in the south) and south Thailand (near the Malaysian border, east of the Thepha River watershed (Gittins 1978; Groves 2001; Marshall and Sugardjito 1986; W. Brockelman pers. comm.).

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Map

Country

Brunei Darussalam
Cambodia
China
Indonesia	IUCN
Japan
Lao PDR
Malaysia	IUCN
Myanmar
Mongolia
Philippines
Singapore
Republic of Korea
Thailand	IUCN
Vietnam

Status

International Status

IUCN Red List Category

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Justification

The species is considered Endangered in light of a continued decline inferred from habitat loss, calculated to be ? 50% over the past 45 years (3 generations), in combination with illegal trade for the pet market. Threats are driven primarily in the Sumatran portion of its range where the species seems to be declining rapidly and is certainly endangered. On the mainland (Peninsular Malaysia and Thailand), there seem to be a number of stable populations, but the range has contracted. The species is entirely confined to closed canopy forest, and thus, habitat conversion, road building and fragmentation are increasingly threatening the species.

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CITES

Appendix IIUCN

CMS

National Status

Ecology Discription

Appearance

Habitat

This species occurs at highest densities in dipterocarp-dominated forests, but their known habitat ranges from swamp and lowland forests to hill, submontane, and montane forests (O?Brien et al. 2004). Additionally, populations in Bukit Barisan Selatan National Park in Sumatra do not seem to avoid forest edges near human habitations (O?Brien et al. 2004). In southern Sumatra, populations were found up to 1,400 meters (O?Brien et al. 2004).

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Population size

O'Brien et al. (2004) performed a population assessment in 2002 on agile gibbons in Bukit Barisan Selatan National Park, Sumatra, Indonesia. Using calling counts in both forest edge and interior habitats, and basing their estimate on forest cover area in the park, they calculated a population of 4,479 agile gibbons (CV = 30%) (O?Brien et al. 2004). In Peninsular Malaysia, Belum and Ulu Muda are strongholds. Portions of the population in Thailand likely number a few thousand individuals, located in approximately three forests fragments/reserves (W. Brockelman pers. comm.).

Density estimates for this species range from 1.4-2.8 individuals/km2 in Bukit Barisan Seletan (O?Brien et al. 2004), and 6-11.4 individuals/km2 in Kerinci-Seblat (Yanuar 2001) to 5.5-18.9 individuals (2-5 groups)/km2 in Sungai Dal on the Malay peninsula (Gittins 1979). Recent surveys in south Thailand reveal the density to be 2 groups/km2 in parts of Hala Bala Wildlife Sanctuary (W. Brockelman pers. comm.)

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Behavior

An average home range size of 29 ha has been determined in a study at Sungai Dal (Gunung Bubu Forest Reserve) on the Malayan peninsula (Gittins 1979, 1982; Gittins and Raemaekers 1980).

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Diet

These arboreal and diurnal primates are primarily frugivorous (preferring fruits high in sugar, such as figs), but they will consume immature leaves and insects as well (Gittins 1979, 1982).

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Reproduction

Threat

Major Threat(s)

On Sumatra, this species is threatened by conversion of their forest habitats by humans and a subsequent opportunistic capture for the pet trade. These threats extend to populations within national parks and forests, including illegal agricultural development inside the parks. In Bukit Barisan Selatan National Park in southwestern Sumatra, deforestation rates are linked to the coffee market; coffee plantations serve to completely strip arboreal primates of their canopy habitats (O?Brien et al. 2004). The expansion of oil palm plantations is a major cause of forest loss on Sumatra. In nearby Java, agile gibbons are one of the most commonly seen gibbons in the wildlife markets (Nijman 2005).

The species? status in West Malaysia is uncertain; in Indonesia, it was certainly affected by fires and deforestation of the 1990s. There has been a probable 50%-plus range reduction in last 10 years (C. Groves pers. comm.), and oil palm plantations are expanding rapidly in the country. In Thailand there is extensive conversion of forests to rubber plantations and other crops (even inside protected areas), as well as hunting for the pet trade.

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Conservation and Measurement

International

Agile gibbons are protected throughout their range by local laws as well as by listing on CITES Appendix I, although the extent to which national or international laws actually protect the species is uncertain.

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National

Conservation law

Protected Area

The species occurs in a number of protected areas, including Bukit Barisan National Park, Kerinci Seblat National Park, Selantan National Park, and Way Kambas National Park in Indonesia; Mudah Wildlife Reserve in Malaysia; and Hala Bala Sanctuary in Thailand. Unfortunately, many of these are merely proposed or gazetted, and their actual protected status is uncertain. Moreover, many of the Sumatran reserves are in montane regions where the species occurs only at low densities. In Bukit Barisan Selatan National Park in southwestern Sumatra, populations are presently secure and healthy but will depend on the regaining of control by the Indonesian government over illegal deforestation of its parks for their continued survival (O'Brien et al. 2004).

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Other Coservation Projects

Citation

Geissmann, T., Nijman, V. and Dallmann, R. 2006. The fate of diurnal primates in southern Sumatra. Gibbon Journal 2: 18-24.

Gittins, S. 1978. The species range of the gibbon Hylobates agilis. In: D. J. Chivers and K. A. Joysey (eds), Recent advances in primatology, pp. 319-321. Academic Press, London, UK and New York, USA.

Gittins, S. 1979. The behavior and ecology of the agile gibbon (Hylobates agilis). Ph.D. Thesis, University of Cambridge.

Gittins, S. 1980. Territorial behavior in the agile gibbon. International Journal of Primatology 1(4): 381-399.

Gittins, S. 1982. Feeding and ranging in the agile gibbon. Folia Primatologica 38(1-2): 39-71.

Gittins, S. 1983. Use of the forest canopy by the agile gibbon. Folia Primatologica 40(1-2): 134-144.

Gittins, S. and Raemaekers, J. 1980. Siamang, lar and agile gibbons. In: D. Chivers (ed.), Malayan forest primates ? Ten years? study in tropical rain forest, pp. 63-105. Plenum Press, New York, USA.

Groves, C. P. 2001. Primate taxonomy. Smithsonian Institution Press, Washington, DC, USA.

Hirai, H., Wijayanto, H., Tanaka, H., Mootnick, A. R., Hayano, A., Perwitasari- Farajallah, D., Iskandriati, D. and Sajuthi, D. 2005. A whole-arm translocation (WAT 8 / 9) separating Sumatran and Bornean agile gibbons, and its evolutionary features. Chromosome Research 13: 123-133.

IUCN. 2008. 2008 IUCN Red List of Threatened Species. Available at: http://www.iucnredlist.org. (Accessed: 5 October 2008).

Marshall, J. 1981. The agile gibbon in south Thailand. Natural History Bulletin of the Siam Society 29: 129-136.

Nijman, V. 2005. In full swing. An assessment of the trade in orangutans and gibbons on Java and Bali, Indonesia. TRAFFIC South-east Asia Report, Kuala Lumpur.

O? Brien, T. G., Kinnaird, M. F., Nurcahyo, A., Iqbal, A. and Rusmanto, M. 2004. Abundance and distribution of sympatric gibbons in a threatened Sumatran rain forest. International Journal of Primatology 25(2): 267-284.

Treesucon, U. 1983. Agile gibbons in Thailand endangered. Conservation News, Association for the Conservation of Wildlife of Thailand, September: 30-32.

Yanuar, A. 2001. The Population Distribution and Abundance of Primates in Kerinci-Seblat National Park, Sumatra. Thesis, University of Cambridge.

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