The Hoolock gibbons (Hoolock) are two primate species from the family of the gibbons (Hylobatidae). Hoolocks are the second-largest of the gibbons family. Gibbon are arboreal species and mostly frugivorous and diet also includes young leaves and flower buds. They play a primary role in forest regeneration as high quality seed dispersers.
Gibbons are territorial species and live in small family groups of two to six individuals. Western and eastern Hoolock gibbons were formerly two subspecies in the genus Bunopithecus. In 2005, Mootnick and Groves placed them into a new genus: Hoolock Hoolock, and Hoolock leuconedys (the eastern).
The western Hoolock gibbon occurs in India, Bangladesh and Myanmar, and the eastern Hoolock gibbon in India, Myanmar and China. The main distribution areas of both Hoolock species are located in Myanmar, mainly in the Kachin, Saggaing, Magway, Rakhine, Irrawaddy, Shan, and Kayar states. The habitat of two species is separated by the Chindwin River and lower part of Irrawaddy River (between the mouth of river and the confluence of Chindwin and Irrawaddy). The western side of the Chindwin and the lower Irrawaddy rivers are inhabited by the Western Hoolock Gibbon, whereas the eastern side is the habitat of the Eastern Hoolock Gibbon. However, further scientific research is still needed to confirm this distribution. The boundary of between the two species in the upper reaches of the Chindwin River (Tanaing Stream) is not well defined, and there is uncertainty among which species of Hoolock gibbon inhabit that region. Most probably both species are living in the area, however no survey have been carried out yet.
According to the International Union for Conservation of Nature – Red List (2013), the western Hoolock gibbon and the eastern Hoolock gibbon found in Myanmar are respectively endangered and vulnerable species.
Hoolock Gibbon Protected Areas in Myanmar
Protected areas that lie west of the Salween River and contain closed-canopy mixed deciduous, semi-deciduous, or evergreen forest are potential habitat for Hoolock gibbons. We identified at least seven significant protected areas (larger than 100 km2), one of which, the Rakhine Yoma Elephant Range (1,755 km2), lies west of the Ayeyarwady River, and therefore probably contains a population of the western Hoolock, H. Hoolock. The Rakhine Yoma area is about 188 north latitude and probably is, or is near, the southernmost occurrence of Hoolock gibbons. Wildlife officials report that gibbons occur there, but no information is available about the population size. There is at least 50,000 km2 of forest area (much of it degraded) in the Rakhine Yoma mountain range in Myanmar west of the Irrawaddy–Chindwin Rivers (BirdLife International 2005), which potentially contains western Hoolocks.
An additional 23,000 km2 lies to the north in the Chin Hills complex, but it is clear from satellite imagery that more than half of this forest is now degraded or destroyed. A couple of small PAs lie in this area. To our knowledge there have been no surveys of primates in any of the areas that are believed to harbor the western Hoolock gibbon. J.T. Marshall Jr. reported hearing eastern Hoolock gibbons (H. leuconedys) along the Salween River from the Thai side in 1974 and 1981 (Marshall and Sugardjito 1986), but it is unclear if any viable population still exists there. There appear to be no conservation areas along the Salween River in the eastern parts of Myanmar.
Between 23,8 and 28,8 north latitude there are six other protected areas, mostly east and north of the Chindwin River. These are (from south to north): Mahamyaing Wildlife Sanctuary (WS) (1,180 km2), Htamanthi Wildlife Sanctuary (1,320 km2), the extended Hukaung Wildlife Sanctuary or Tiger Reserve (about 21,802 km2), Bumhpabum Wildlife Sanctuary (1,854 km2), Hpongan Razi Wildlife Sanctuary (2,704 km2) and Hkakaraborazi National Park (3,812 km2). The last area is the northernmost part of Myanmar, and gibbons are reported only in the park’s southern parts.
The northern limit of gibbons in the area, which is now in the center of Hkakaraborazi Park, was reported by naturalist-explorer Frank Kingdon-Ward (1937) to be the Seinghku confluence of the Nam Tamai River, which is slightly north of 288 north latitude. Many mountains in northern Myanmar exceed 4,000 m in altitude, and Hoolock gibbons have been reported to occur at or above 8,000 ft (2,438 m: Kingdon-Ward 1949; Tun Yin 1967). There are some suggestions that they may move up and down mountains seasonally, although this has not been substantiated to our knowledge. For example, Kingdon-Ward (1949: 244) reported: ‘‘
The Hukaung–Bumhpabum reserves are broadly contiguous and from satellite images about 75% of the whole area is covered with closed forest, the rest being agricultural area in the center of the valley, degraded swiddens, and bamboo forest. Hence, these reserves contain roughly 20,000 km2 of suitable forest habitat for gibbons—effectively the largest intact evergreen forest of mainland Southeast Asia. Actual protection and management of this forest complex will be a difficult and complex problem requiring considerable local education and extension work, particularly as more than 50,000 people already reside in the Hukaung Valley.
Because the Nature and Wildlife Conservation Division of the Forest Department suffers from severe constraints in its capacity to enforce conservation laws over such a vast area, effective conservation measures need to be incorporated into the development goals of all government agencies active in the region, as well as the programs of local political minority groups.
The upper Chindwin River is fed by the Tanai River, which drains areas in the eastern part of the Hukaung Valley. Most of the watershed lies within the putative area of hybridization or inter-gradation between the eastern and the western Hoolock gibbons (Groves 1967). The gibbons in the areas in the mountains north and west of the Hukaung Valley are especially unstudied and call for much more research on their genetics, phenotypes, and vocalizations to understand the relationship between the two forms now recognized as species.
The wild population of this gibbon species is highly affected by human activities such as gold mining, logging, and hunting, which are pushing the population to constant decline. In Myanmar, shifts in cultivation are a major threat for gibbon species. Most local people living in the gibbon habitat areas rely on shifting cultivation for their main food supply. Additionally, hunting pressure for food, medicinal purposes and wildlife trade also contribute to endanger the status of this species. Extensive logging activities are the cause of increasing habitat loss, and contribute to the fragmentation of the gibbons’ habitat, thus restricting movements and exacerbating wildlife-human conflict. The extension of rice fields, the conversion of forests into agriculture land, and gold mining are all further factors degrading gibbons’ habitat and population.
Conservation Actions Taken by WCS Myanmar
The Wildlife Conservation Society is implementing Hoolock gibbon survey in collaboration with the Nature and Wildlife Conservation Department of the Forestry Ministry. This set of conservation activities are aimed at assessing the conservation status of the Hoolock gibbons in Myanmar, while also strengthening the capacity of the conservation movement in primate surveying, monitoring and conservation in Myanmar. The main goals are:
- To survey gibbon population densities and develop long-term monitoring plan for gibbon species;
- To conduct detail assessment of threats related to habitat loss and hunting and their impact on gibbon population;
- To learn about the attitude of local people on gibbon around the wildlife sanctuary;
- To promote the education program for gibbon conservation;
- To record the gibbon distribution on their habitats quality and food abundance;
- To monitor Hoolock gibbons as an indicator for conservation intervention success;
- To implement effective law enforcement for gibbon conservation through SMART Patrolling.
WCS have done first gibbon population census and habitat assessment survey during in 2002-2003 at Babulonhtan area between Machanbaw and Naung Mong, Kachin. Maharmyaing Wildlife Sanctuary gibbon survey had done in 2004-2005. During 2005-2006, gibbon survey was implemented in Hukaung Wildlife Sanctuary. Moreover, WCS has performed a gibbon population census and habitat assessment at the Htamanthi Wildlife Sanctuary and Naga Land area in 2013-2014. Currently, gibbon monitoring and law enforcement activities are being conducted at the Htamanthi Wildlife Sanctuary. WCS is also carrying out an education program targeting villages surrounding the Wildlife Sanctuary.