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Hoolock hoolock

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA PRIMATES HYLOBATIDAE

Scientific Name: Hoolock hoolock
Species Authority: (Harlan, 1834)
Common Name(s):
English Western Hoolock Gibbon, Hoolock Gibbon, Western Hoolock
French Gibbon Hoolock Occidental, Hoolock
Spanish Gibón Hulock
Synonym(s):
Bunopithecus hoolock subspecies hoolock (Harlan, 1834)
Hylobates hoolock (Harlan, 1834) [pro parte
Taxonomic Notes: This taxon is now considered monotypic; it was formerly considered conspecific with Hoolock leuconedys. The previous generic name, Bunopithecus, was changed by Mootnick and Groves (2005) to Hoolock (Haimoff et al. 1984).

Assessment Information [top]

Red List Category & Criteria: Endangered A2acd+3cd+4acd ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Brockelman, W., Molur, S. & Geissmann, T.
Reviewer(s): Mittermeier, R.A. & Rylands, A.B. (Primate Red List Authority)
Justification:
Listed as Endangered as there is reason to believe the species has declined by at least 50% over the past 40 years (approximately three generations) due primarily to hunting and habitat loss. Over the coming 40 years, this decline is likely to reach similar proportions due to continuing habitat loss.
History:
2000 Endangered

Geographic Range [top]

Range Description: This species is found in eastern Bangladesh, northeastern India (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura), and northwestern Myanmar (west of the Chindwin River). It might possibly occur in China (extreme southeastern Tibet). The distribution in India is restricted to points south of the Brahmaputra and east of the Dibang (Dingba Qu) Rivers (Choudhury 2001). Animals that once were common in the plains of Arunachal Pradesh (northeasternmost India) before that habitat was cultivated for agriculture and tea are not so anymore (Islam and Feeroz 1992).

The boundary between the two species of Hoolock is the Chindwin River, which flows into the Ayerawady (Irrawady) River. At the headwaters in the north there is a hybrid zone or cline between the two species (since they are almost certainly not reproductively isolated). Das et al. (2006) reported the discovery of a population of H. leuconedys in Arunachal Pradesh, northeast India, which has traditionally been considered to be part of the range of H. hoolock.
Countries:
Native:
Bangladesh; India (Assam); Myanmar
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: There are estimated to be about 200-280 hoolocks in Bangladesh (Islam et al. 2006; Molur et al. 2005). In China, a population has been identified in Medog Nature Reserve in southeastern Tibet, just across the border from Arunachal Pradesh, but the identity of this taxon is not established and there has been no survey conducted to determine the population numbers (W. Bleisch pers. comm.).

This species occurs in several of India’s northeastern states, but populations there tend to be isolated. It is common in certain areas of occurrence, but rare in others due to intense hunting by local tribes (Choudhury 1991), and is considered rare throughout its range (Choudhury 2001). The species was found in all forested patches in northeastern India about 30 years ago, but they are reduced to a few forest fragments now. The total population in northeastern India was estimated to be about 2,600, of which the majority—about 2,000—occurs in the state of Assam (Molur et al. 2005). A population of about 170 gibbons has more recently been identified as H. leuconedys (Das et al. 2006) and should be subtracted from the population estimate if this identity is proven. Moreover, there are surveys needed in Mehao region, where there is uncertainty as to which species the gibbons there represent (Das et al. 2006; Das pers. comm.). Namdapha National Park in the Changlang District of Arunachal Pradesh is a relative stronghold for this species in India, offering the population there its largest contiguous stretch of protected habitat (Chetry et al. 2003).

There are no population estimates available for Myanmar. It is possible that the largest and most viable populations of western hoolock are to be found in this country, where at present almost no attention is paid to it (W. Brockelman pers. comm.). There are several thousand square kilometers of unsurveyed forest habitat in the central-west and north-west of this country, with a particular need to survey the western areas west of Chindwin/Ayerawady River. There are reports of gibbons in Rakhine Yoma Elephant Range, but there is no knowledge of the actual population level there (W. Brockelman pers. comm. 2006). The western part of Hukuang Tiger Reserve with a large area of forest (>1,000 km2) has not been surveyed, but is likely to have this species. The northern limit is just south of Hkakaraborazi National Park.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: This species is a forest-dweller that, depending on its locale, inhabits tropical evergreen rainforests, tropical evergreen and semi-evergreen forests, tropical mixed deciduous forests, and subtropical broadleaf hill forests. It has also been noted in bamboo “brakes” and hollock (Terminalia myriocarpa) and ajhar (Largerstroemia flosreginae) plantations. One gibbon pair in the Borajan Reserved Forest (north-east India) was observed to habitually descend from the trees to move over scrub and short bamboo especially while trying to reach the isolated food trees inside a village. This pair was found sleeping at heights of 0 m or less in bamboo clumps (Kakati 1997). Although gibbons may be moving through, or sleeping in, bamboo forest or plantations, they cannot survive in monocultures (W. Brockleman pers. comm.). Additionally, the species has been observed in two plains forest locations (Choudhury 1991). Its preferred habitat, however, is dense evergreen and semi-evergreen forests (Choudhury 2001). It has been recorded at altitudes of up to 2,500 m in Manipur, northeast India (Choudhury 2001).

Home ranges in most populations range from 8-63 ha (Ahsan 2001; Alfred 1992; Alfred and Sati 1986, 1990; Feeroz and Islam 1992; Gittins and Tilson 1984; Islam and Feeroz 1992; Kakati 2004; Mukherjee 1986; Tilson 1979), but unusually large home ranges of 200-400 ha were reported from Tripura and Arunachal Pradesh, northeast India (Mukherjee 1982; Mukherjee et al. 1988). The western hoolock is a frugivorous species, with ripe fruits composing a majority of its diet (Ahsan 2001; Alfred and Sati 1986, 1994; Feeroz and Islam 1992; Islam and Feeroz 1992; Kakati 1997; Tilson 1979). A dominantly folivorous diet was reported during studies carried out in Assam’s Borajan Reserved Forest, and in Tripura (Kakati 1997; Mukherjee 1986), and gibbons living in small forest fragments were observed to experience a period of almost total lack of fruit in their diet at the end of the dry season (Kakati, 2004). Low fruit availability may contribute to the relatively large home range sizes of some populations. In northeast India, the hoolock gibbon is recognized as being an important disperser of undigested seeds from large and small fruit-bearing trees (Das 2003).
Systems: Terrestrial

Threats [top]

Major Threat(s): In Bangladesh, the main threats are the combined effects of habitat loss, fragmentation, human interference and hunting (Islam and Feeroz 1992; Molur et al. 2005). Hunting is universal all over Bangladesh as well as India, and may be in Myanmar also. In China, the Tibetan population could be under threat from hunting for food or non-targeted hunting, but this is not established.

In some Indian locales, these animals are rare due to large scale hunting for food and because some ethnic groups believe the gibbons have medicinal properties (Gupta 2005; J. Das pers. comm.). Additionally, jhoom cultivation threatens the habitats of Indian populations, some of which are relatively isolated already (Choudhury 1991). Affecting all northeastern Indian primate populations are harvesting of bamboo for paper mills, oil mining and exploration, and coal mining, which deplete habitat and cause pollution and disturbance (Choudhury 2001). Habitat fragmentation and loss are major threats in India (Molur et al. 2005). Small and restricted groups may not be viable because of genetic and demographic instabilities and because they are more affected by hunting pressure and habitat loss. Many small forest fragments are reported to have only one or a few gibbon groups. These have limited chances of surviving more than a few generations without translocation.

In Myanmar, shifting cultivation is a major threat, and so is hunting. Although logging is restricted on the western side of the Chindwin, it is still considered a threat for this species. Political and ethnic conflicts have prevented the Myanmar government to promote development and conservation activities effectively in areas of northwestern and central western Myanmar along the borders with India and Bangladesh. Thus, most conservation efforts have been concentrated within the range of H. leuconedys.

Conservation Actions [top]

Conservation Actions: This species is listed on CITES Appendix I and on schedule I of the Indian Wildlife (Protection) Act of 1972. Overall, it is found in 30 protected areas in India (Choudhury 2001) and many others throughout its range.

Citation: Brockelman, W., Molur, S. & Geissmann, T. 2008. Hoolock hoolock. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 30 July 2014.
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