The boundary between the two species of hoolock gibbon is uncertain in the Chindwin headwaters in the north, and possibly includes a zone of intermediates or variable population (T. Geissmann pers. comm.). More fieldwork is needed to investigate populations on both sides of the river and in the headwaters of the Chindwin, where there is likely to be one or more hybrid zones or clines (W. Brockelman pers. comm.).
Habitat and Ecology
It is a frugivorous species, with ripe fruits composing a majority of its diet. Individuals also eat a large proportion of figs and some amount of leaves, shoots, and petioles. This diet contributes to a relatively large home range of some populations.
No intensive studies have been carried out on the behaviour or ecology of H. leuconedys, but it may be assumed to be similar to that of H. hoolock, with diet varying somewhat by habitat (W. Brockelman pers. comm.).
IUCN Red List Assessment
Red List Category
Red List Criteria
The total population of H. leuconedys in Myanmar is over 10,000 individuals, and perhaps up to 50,000 or so; however, much more survey work is needed. There have been some Wildlife Conservation Society surveys in Hukaung Valley Wildlife Sanctuary, which have approximately two groups/km2 (Htun pers. comm. 2006). There are approximately two groups/km2 in Mahamyaing Wildlife Sanctuary based on vocal surveys, with a total population of 4,000–8,100 individual gibbons (about half of which would be adult animals) (Brockelman 2006 unpub. draft).
The species is doing relatively well in Myanmar, but there is no guarantee of continued political protection in the next few decades (W. Brockelman pers. comm.). Political instability is presently slowing down logging (W. Bleisch pers. comm.).
Eastern hoolock gibbon
The eastern hoolock gibbon (Hoolock leuconedys) is a primate from the gibbon family, Hylobatidae. The species is found in extreme eastern corner of Assam and parts of Arunachal Pradesh, Myanmar east of the Chindwin River, and in south west Yunnan of China; the Indian records may represents Hoolock hoolock.
Mootnick and Groves stated that hoolock gibbons do not belong in the genus Bunopithecus, and placed them in a new genus, Hoolock. This genus was argued to contain two distinct species which were previously thought to be subspecies: Hoolock hoolock and Hoolock leuconedys. Another difference between the two species (eastern and western hoolock gibbons) is that recent studies have shown that the eastern hoolock gibbons range is restricted in India to the northern side of the Lohit river but doesn't go past the Himalayan range
- Brockelman, W. & Geissmann, T. (2008). Hoolock leuconedys. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
- Groves, C. P. (1967). "Geographic variation in the hoolock or white-browed gibbon (Hylobates hoolock harlan 1834)". Folia Primatologica 7: 276–283. doi:10.1159/000155125. PMID 5626313.
- Mootnick, A. R. and C. P. Groves (2005). "A new generic name for the hoolock gibbon (Hylobatidae)". Int. J. Primatol 26: 971–976. doi:10.1007/s10764-005-5332-4.
- Mootnick, A. R. (2006). "Gibbon (Hylobatidae) species identification recommended for rescue or breeding centers". Primate Conserv 21: 103–138. doi:10.1896/0898-622.214.171.124.
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