The Hoolock genus can be split into two species: the Western Hoolock Gibbon (Hoolock hoolock) and the Eastern Hoolock Gibbon (Hoolock leuconedys). The Western Hoolock is classified as Endangered on the IUCN Redlist (A2acd+3cd+4acd ver 3.1) and is one of the 25 most threatened species worldwide, while the Eastern Hoolock is classified as Vulnerable (A3cd ver 3.1). Both are listed on Appendix I of CITES meaning that these species are highly threatened with extinction in the near future.
In the past, only one Hoolock gibbon species (Hoolock hoolock) was recognised, and the Hoolock leuconedys was considered as a subspecies. Both belonged to the genus Bunopithecus according to their supposed evolution from the extinct species Bunopithecus sericus. But recent research has shown that the hoolock gibbons are actually not closely related to Bunopithecus, and so in 2005 Hoolock was elevated to genus level and the subspecies H. leuconedys raised to species level (Mootnick and Groves, 2005).
The Hoolock gibbon inhabits the most north eastern range of all gibbon species: its distribution stretches from Bangladesh to Northeast India, to Myanmar and Yunnan in South China, and the two species are separated by the Chindwin River. The Western Hoolock occurs in eastern Bangladesh, north eastern India (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura) and in north western Myanmar (Choudhury 2001, 2006). The Eastern Hoolock occurs in western Yunnan (southern China) and north eastern Myanmar. It is likely that there is a hybrid zone between the two species in eastern Arunachal Pradesh (northeast India), where Das et al. (2006) reported the discovery of a population of H. leuconedys. However, further survey work is needed to confirm this report (W. Brockelman pers. comment, cited by Brockelman et al. 2011).
The population estimates of Hoolock gibbons are very tentative because survey data are rare. Based on the most recent estimations the total population of Hoolocks is thought to be between 20,000 – 60,000 individuals, plus an unknown number of individuals in western Myanmar (west of the Chindwin River).
Estimations for the different regions are as follows:
- Western Hoolock (H. hoolock):
- Total: 7,400 – 7,450 individuals plus unknown number in Myanmar
- India: 7,000 individuals (Chetry et al. 2007, cited by Chetry and Chetry 2011)
- Bangladesh: 350 individuals (Islam et al. 2006, 2008, 2011), 50-100 individuals in remote Chittagong Hill Tracts (Walker et al. 2009; Islam et al. 2011)
- Southeast Tibet: populations are reported, but no data available (Bleisch pers. comment, cited by Brockelman et al. 2008)
- Myanmar: probably the largest H. hoolock population, but no data or estimations available (Lwin et al. 2011; Brockelman pers. comment 2008)
- Eastern Hoolock (H. leuconedys):
- Total: 13,200 – 53,200 individuals
- India: 3,000 individuals (Biswas et al. 2007, 2010; Chetry & Chetry 2011; Chetry et al. 2008, 2011)
- China: less than 200 individuals (Fan et al. 2011)
- Myanmar: more than 10,000, perhaps 50,000 individuals (Brockelman et al. 2008)
It should be noted that the indications for increasing numbers of some populations are only effects of increased survey activities in these regions (Walker et al. 2009), and not an actual population increase.
According to their IUCN status, both Hoolock species have suffered a population decline of up to 50% in recent decades. Projections for the future are similar and populations are expected to decline further in the next 3-4 decades. The major threats to the Hoolock gibbons are habitat loss and hunting. Deforestation leads to the fragmentation of forest and minimizes the gibbon’s habitat, and even in the remaining forest the canopy cover is damaged and fruiting trees are cut down (Walker et al. 2009). Industrial activities cause disturbance and pollution and do not only encroach upon gibbons but upon all flora and fauna. Hunting is a big problem because it decreases present and future population growth by reducing the number of mature individuals and impeding natural reproduction. Deforestation has a serious effect not only because it reduces areas of suitable habitat, but because habitat fragmentation leads to the destabilization of populations. Groups become smaller and are isolated from one another by farmland, pasture, roads and human settlement which they cannot cross, and this leaves many tiny unstable populations which are extremely vulnerable.
Threats for Western and Eastern Hoolocks differ slightly, and are often site specific:
- Western Hoolocks suffer mainly from habitat loss, fragmentation, human activities and hunting in Bangladesh (Islam & Feeroz 1992; Molur et al. 2005; Brockelman et al. 2008); from slash-and-burn-agriculture, tea plantations, bamboo extraction, oil and coal mining in India (Choudhury, 2001; Molur et al. 2005); and shifting cultivation, hunting, logging, and timber extraction in Myanmar (Geissmann et al. 2009). It is estimated that populations of H. hoolock have decreased by approximately 90% in the last 40 years due to massive habitat loss, from 100,000 to less than 5,000 individuals. In only four years (from 2001 to 2005), this species became extinct in 18 locations in India and Bangladesh that were previously part of its range (Walker et al. 2009).
- Eastern Hoolocks are also threatened primarily by habitat loss and hunting for medical purposes and for meat (M. Richardson, pers. comment, cited by Brockelman & Geissmann, 2008). Investigations in Myanmar showed that commercial logging is a severe problem, but only outside protected areas. Nevertheless, the population of 50,000 people living within Hujaung Valley Tiger Reserve is a challenge for conservation efforts in this protected area, mainly due to hunting traditions of local people. Conservation activities are also disturbed by gold mining in Kachin State in Myanmar (Brockelman, 2008). The population trend of gibbons in China is an example of the dramatic decline of this species. In the past gibbons (probably Hoolock but also Nomascus) were distributed up the Yellow River (www.gibbons.de Gibbon Network), and in the 1980´s the eastern gibbon occurred in nine counties of the province of Yunnan (Li & Lin, 1983; Tan, 1985; Yang et al., 1985, 1987; Fooden et al., 1987; Ma & Wang, 1986, 1988). By the 1990´s only four counties still contained H. leuconedys (Lan et al. 1995), and a census carried out in 2008-2009 showed that there were only 40 groups left distributed throughout three counties. This indicates a total population of less than 200 individuals in China and a population decline of at least 50% since the 1990´s (Fan et al. 2011a).
The H. hoolock is listed on CITES Appendix I and on schedule I of the Indian Wildlife (Protection) Act of 1972. It is classified as Endangered (EN) and the 2002 gibbon symposium of the Congress of the International Primatological Society in Beijing included the western hoolock gibbon in the top 10 most threatened gibbon species of the world (Walker et al. 2009). H. leuconedys is listed on CITES Appendix I and the IUCN classifies this species as Vulnerable (VU).
Action is urgently needed to prevent further decline of the Hoolock gibbon. Primarily, scientific activities such as surveys and monitoring of gibbons and their habitat should be increased. Accurate estimates of population sizes and on the presence/absence of the species in the different locations are necessary for conservation management planning. Of equal importance to scientific work is the limitation of habitat destruction and more governmental help and in some cases a change in governmental attitude is needed for this (Islam et al. 2011). More protected areas should be created and the long-term restoration of degraded habitat implemented in order to prevent further decline of isolated populations. Law enforcement is also of great importance to put a stop to hunting and illegal logging, and should be accompanied by support for the protected areas and improved patrols.
Long-term conservation can be successful only in cooperation with the local community, and conservation efforts should include educational programs, and also measures to compensate locals for the prohibition of hunting and other direct resource exploitation from the forests (Walker et al. 2009; Islam et al. 2011). For example, tourism could be an alternative income and could have positive effects on local development (Brockelman & Geissmann, 2008).
The conservation status of Hoolock gibbons differs between locations, but several ambitious initiatives and programs have been started to try and halt the decline of the remaining populations.
Some recent examples are:
In 2002, the participants of a Conservation Assessment and Management Plan (CAMP) workshop in Coimbatore pointed out the vulnerable situation of the H. hoolock and initiated a Population and Habitat Viability Assessment (PHVA) workshop. This PHVA workshop took place in 2005 in Bangladesh. Among other measures the translocation of isolated individuals and groups from degraded habitat to more viable areas was discussed. This resulted in a Bengali-Indian collaboration for scoping and training in translocation. Although translocations have not yet been carried out these campaigns have greatly helped in raising public awareness (Walker et al. 2009). Besides protected areas the conservation of H. leuconedys focuses on educational efforts. A WCS project has been implemented around the Mahamyiang Sanctuary to reduce hunting and to support the Wildlife Sanctuary for better patrols. There is also a special focus on conservation education in local schools (Brockelman et al. 2008).
H. hoolock occurs in the following protected areas:
- ASSAM: Barekuri Gibbon Conservation Park, Borajan Wildlife Sanctuary, Dibru-Saikhowa National Park, Kaziranga National Park, Gibbon Wildlife Sanctuary, Namdapha National Park and Manas wildlife Sanctuary.
- BANGALDESH: Hukaung Valley Tiger Reserve, Kaptai NP, Kassalong Reserve Forest, Lawachara National Park, Rema-Kalenga Wildlife Sanctuary, West Bhanugach Reserve Forest and Satchari National Park.
- MYANMAR: Rakhine Yoma Elephant Range.
- INDIA: Trishna Wildlife Sanctuary, Tripura.
H. leuconedys occurs in the following protected areas:
- MYANMAR: Bumhpabum Wildlife Reserve, Hkakaborazi National Park, Hponkan Razi Wildlife Reserve, Htamanthi Wildlife Reserve, Hukaung Valley Wildlife Sanctuary, Indawgyi Wildlife Sanctuary and Mahamyaing Wildlife Sanctuary.
- CHINA: Gaoligongshan Nature Reserve and Tongbiguan National Nature Reserve.
- INDIA: Mehao Wildlife Sanctuary, Arunal Pradesh, and Turung Reserve Forest, Arunal Pradesh.
List of ongoing projects and studies:
- Indo-U.S. Primate Project: different activities of education, awareness, research, training and socio-economic development programmes (description by Chetry & Chetry 2011).
- Hoolock Gibbon Conservation Status Review Project 2008-2010 (description by Lwin et al. 2011, description of the survey and training in Myanmar: Geissmann et al. 2009) – a Conservation Action Plan was designated - Potess, L. Fernando; Momberg, Frank; Grindley, Mark; Geissmann, Thomas: Hoolock Gibbon Status Review project. Myanmar Conservation Program, BANCA, FFI, PRCF, and Yangon University, Myanmar. E-mail: email@example.com (cf. www.gibbons.de)
- Public awareness campaigns and educational programs by Wildlife Trust of Bangladesh (WTB), example in Bangladesh (described by Chowdhury et al. 2011).
- Strategic Planning workshop for conservation of western hoolock gibbons in Assam, (description by Das et al. 2011).
- Fauna & Flora International (FFI), (description by Browne et al. 2011).
- The Gibbon Conservation Center www.gibboncenter.org
- The Gibbon Conservation Alliance www.gibbonconservation.org, including The Gibbon Journal (annually since 2005, free download)
- Kumar, Awadhesh: Spatial mapping of habitat distribution, assessment of population status and modeling of conservation strategies for eastern hoolock gibbon (Hoolock hoolock leuconedys) in Arunachal Pradesh, Northeast India. E-mail: firstname.lastname@example.org (cf. www.gibbons.de)
- Kumar, Awadhesh: Assessment of population structure and regeneration pattern of most preferred food plant species of hoolock gibbons in protected and non-protected areas of Northeast India. E-mail: email@example.com (cf. www.gibbons.de)
- Huro Program. Conservation Program of the Western Hoolock Gibbon, Association SVAA / Huro Program, 5 avenue E. Guynemer, 02400 Verdilly, France www.association-svaa.com (cf. www.gibbons.de)
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Biswas, J., Sangma, A., Ray P. C., Das, J., & Tapi, T. 2010. Status survey and bio-geography of hoolock gibbon in Arunachal Pradesh. Final Report of Primate Research Centre NE India and U.S. Fish and Wildlife Services Collaborative Project, 49 pp.
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