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Description |
Geographic Range [top]
Range Description: The species as a whole is found in northern Sumatra (Indonesia), throughout Peninsular Malaysia (except for a narrow strip between the Perak and Mudah Rivers, where H. agilis occurs), north through southern and eastern Myanmar (east of the Salween River), most of Thailand (though not in the north-east), and marginally into southern China. The break in distribution between Perak and Muda/Thepa Rivers on the Malaysian Peninsula is genuine (T. Geissmann pers. comm.). The species also occurs in a small area of northwestern Lao PDR (west of the Mekong River). The range formerly extended into southeastern Thailand, where it was parapatric with H. pileatus (Brockelman 1978; Marshall and Sugardjito 1986; Marshall et al. 1972; T. Geissmann pers. comm.). It is unclear whether the population on Phuket (Thailand) is native, but they certainly have been introduced or reintroduced.
In China, the species is currently known only from Nangunhe Nature Reserve in the Prefectury of Lincang, south-west Yunnan (Geissmann et al. 2006).
Countries occurrence:
Native:
Indonesia (Sumatera); Lao Peoples Democratic Republic; Malaysia (Peninsular Malaysia); Myanmar; Thailand
Possibly extinct:
China (Yunnan - Native)
Additional data:
? Upper elevation limit (metres): 1500
Range Map: Click here to open the map viewer and explore range.
Population [top]
Population: Population densities for this species range from 2.4 groups/km2 in Ketambe, Sumatra (Palombit 1992) to 0.7-2.6 groups/km2 in Kuala Lompat and Tanjong Triang on the Malayan peninsula (Ellefson 1974; MacKinnon and MacKinnon 1980; Raemaekers 1977) to 6.5 groups/km2 in Khao Yai National Park, Thailand (Brockelman cited in Chivers 2001). A few smaller, fragmented populations survive in southern Peninsular Thailand and northwestern Malaysia, perhaps together numbering in the low thousands. There are no recent estimates of the populations in the Tenasserim section of Myanmar, northern Sumatra and in southern Peninsular Malaysia (W. Brockelman pers. comm.).
In China, during the 1960s, there were estimated to be 200 individuals on both sides of the Nangunhe River. In 1988, the date of last sighting, it was estimated that there were less than 10 groups. And in 1992, the last survey date, the authors did not find any direct evidence for the species persistence, but estimated that three groups may remain with about 10 individuals in total. Although not specified in the original publications, this estimate appears to be based on interview data (Geissmann et al. 2006; Guo and Wang 1995; Lan and Wang 2000).
No population estimates are currently available for Indonesia, Malaysia, and Myanmar. While for Lao PDR, there are no reliable estimates, but for Nam Poyi National Protected Area (which is the only protected area from which they are recorded), the species is uncommon to rare, perhaps numbering in the mid- to high-hundreds (Boonratana 1997). In some parts of Thailand there are several populations where numbers are at least in the thousands, though in northern Thailand they are now very rare. The largest population is in Kaeng Krachan National Park, which probably has on the order of 3,000-4,000 individuals. The Western Forest Complex may well have on the order of 10,000 animals, and likely upwards of 1,000 survive in the western part of Khao Yai National Park, as well as in Phukhieo Wildlife Sanctuary and Nam Nao National Park. A few smaller populations survive in the south, for example Khao Sok (W. Brockelman pers. comm.).
Current Population Trend: Decreasing
Additional data:
? Population severely fragmented: No
Habitat and Ecology [top]
Habitat and Ecology: This species is found in evergreen, semi-evergreen, and mixed evergreen-deciduous forest (sometimes known as "dry evergreen" forest, in the northern parts of its range), and is known to utilize regenerating secondary forest and selectively logged forest (Johns 1985). In northwestern Thailand, white-handed gibbons utilize patches of dry evergreen, mixed deciduous, and bamboo forest near Karen settlements if they are not hunted (Yimkao and Srikosamatara 2006). This is predominantly a lowland species (below 1,000-1,500 m).
Like most other species of gibbon they consume a largely frugivorous diet that includes mainly figs, as well as young shoots, leaves, some flowers, and insects. Gibbons, unlike most macaques and leaf monkeys that often share their habitats, swallow nearly all the seeds that they ingest, making them potentially important as seed dispersers. Certain species of fruits that require the consumer to remove a tough outer cover appear to rely almost entirely on gibbons for seed dispersal (Bartlett 1999; Ellefson 1974; Gittins and Raemaekers 1980; MacKinnon and MacKinnon 1980; Palombit 1992, 1997; Ungar 1995).
Generation length in white-handed gibbons is on the order of 15 years. They mature late, with females maturing at 8-10 years and males at 8-12 years, and have one offspring every 3 to 5 years (Brockelman et al. 1998; W. Brockelman pers. comm.). If a female loses a baby she may come into estrus sooner, but the average inter-birth interval in a population at carrying capacity is about 3.5 years (W. Brockelman pers. comm.). Average group size in H. lar generally increases with latitude, illustrating that group size is not a very useful species-specific character in gibbons. This reflects a general trend of increasing birth rate with latitude found in many vertebrate groups. Average group size has been reported at 2.7 (Chivers 1978) and 3.3 (Ellefson 1974) in Peninsular Malaysia, 3.7 in central Thailand (Brockelman and Srikosamatara 1993), and 4.4 (Carpenter 1940) and 4.9 (Yimkao and Srikosamatara 2006) in northern Thailand. The average home range sizes are 44-54 ha on the Malayan peninsula (Ellefson 1974; Gittons and Raemaekers 1980; MacKinnon and MacKinnon 1980) and about 16 ha in the Khao Yai National Park in Thailand (Chivers 1984).
Systems: Terrestrial
Threats [top]
Major Threat(s): The major threat to this species is hunting (having replaced even forest clearance as the top threat); they are hunted both for subsistence food use and for the pet trade. Hunting pressure varies across the range, but takes place even within protected areas. Much of the hunting is done by villagers exploiting Aquilaria spp. trees prized for their aromatic wood, and other forest products (W. Brockelman pers. comm.).
Construction of roads through protected areas (for example, the Security Highway through Nam Poyi in Lao PDR, the north-south highway in Peninsular Malaysia) may also pose a threat since it promotes forest clearance and strip development, possibly increases fragmentation, and increases access by hunters into protected areas. Ongoing localized forest loss due to shifting agriculture and commercial plantations of palm oil poses a threat. On northern Sumatra, most of the lowland forests have been logged out and the threat of Ladia Galaskar, a network to link the west and east coasts of Aceh province, means that much of the remaining forest is at risk.
Conservation Actions [top]
Conservation Actions: Hylobates lar, like all gibbons, is a nationally protected species in all the countries across its range, and is listed under CITES Appendix I. In most of its range it is confined to protected conservation areas (for example in Thailand, where no significant populations survive outside of protected areas). However, in most countries, these areas are not well patrolled, even if they are well managed for tourism. There is an urgent need for improved protection of these areas, ideally involving local communities that should benefit from as well as participate in management. Illegal use of forest products, as well as poaching, is common in most protected areas. Inadequate management and protection, rather than forest destruction, are the main long-term threats and conservation efforts must seek to identify the hunters and incorporate them into new management priorities.
Further survey work is needed to determine current population numbers within protected areas across the range. One such priority area is southwest Yunnan, where it is unclear whether the species still survives (W. Brockelman pers. comm.).
Citation: Brockelman, W. & Geissmann, T. 2008. Hylobates lar. The IUCN Red List of Threatened Species 2008: e.T10548A3199623. http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T10548A3199623.en. Downloaded on 19 July 2016.
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