Hoolock hoolock
Creators: name: Russell A. Mittermeier
name: Anthony B. Rylands
name: Don E. Wilson
Publisher: name: Lynx Edicions
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Primates
Hylobatidae
Hoolock
Hoolock hoolock

description: 1.
Western Hoolock Gibbon
Hoolock hoolock
French: Gibbon hoolock / German: Westlicher WeiRbrauengibbon / Spanish: Gibén huloc occidental
Other common names: Hoolock Gibbon, Western White-browed Gibbon
Taxonomy. Simia hoolock Harlan, 1834,
India, Garo Hills, Assam.
Genetic studies by L. A. Prouty and colleagues in 1983 recognized the hoolock gibbons as a distinct subgenus, under the name Bunopithecus (originally proposed for a Middle Pleistocene gibbon from Yanjinggou in Sichuan, China). In the taxonomic review of D. Brandon-Jones and coworkers in 2004, hoolock gibbons were listed under the genus Bunopithecus. In 2005, A. Mootnick and C. P. Groves showed that the name Bunopithecus was unavailable and provided a new generic name Hoolock. Mootnick and Groves also argued that leuconedys, formerly considered a subspecies in the eastern distribution of H. hoolock, should be considered a distinct species. Monotypic.
Distribution. Bangladesh and NE India (states of Assam, Arunachal Pradesh, Nagaland, Meghalaya, Manipur, Mizoram, and Tripura) between the Brahmaputra and Salween rivers, and to the S of the Brahmaputra and E of the Dibang rivers, extending into NW Myanmar, W of the Chindwin River. W. Bleisch has reported an isolated population of gibbons to the N, in the Medog Nature Reserve in SE Xizang Autonomous Region (= Tibet), across the border from Arunachal Pradesh, but their identity has not been established.
Descriptive notes. Head-body c.81 cm; weight 6-9 kg (males) and 6-1 kg (females). Male and female Western Hoolock Gibbons are comparable in size but quite dissimilar in color. Adult males and juveniles are jet black except for a pair of whitish brow streaks that turn up slightly at the ends; these are quite close together and connected by white hairs. Adult males also have a little white on the chin or under the eyes, and the preputial tuft is black or only faintly grizzled. In contrast, females become copperytan at maturity, with dark brown cheeks and a white face-ring that continues around and under the eyes as suborbital streaks.
Habitat. Primary tropical rainforest, evergreen and semi-evergreen forests, subtropical broadleaf hill forest, and tropical moist deciduous forest; occasionally in bamboo thickets and plantations of Terminalia myriocarpa (Combretaceae) and Lagerstroemia flos-reginae (Lythraceae). Western Hoolock Gibbons sometimes travel on the ground to reach isolated fruiting trees, especially where their habitats are degraded and fragmented and close to villages where they may make use of cultivated fruit trees. Although they may move through, or sleep in, bamboo forest or plantations, they cannot survive in monocultures. Western Hoolock Gibbons occur at elevations of 500-2700 m.
Food and Feeding. The Western Hoolock Gibbon is primarily frugivorous, preferring ripe and fleshy fruits, but they also eat leaves and leaf petioles, flowers and flower buds, seeds, shoots, moss and lichens, insects, spiders, and bird eggs. Regarding the time spent eating different food items; the typical diet is 65% fruits, 13% leaves, 12% petioles, 5% flowers, and 5% animal protein. When fruits are scarce, either seasonally or because they are in degraded and fragmented forest patches, they eat more leaves. Figs (Ficus, Moraceae) are particularly important. They feed on bamboo shoots in the Borajan Wildlife Sanctuary, and fruits comprise only 40% of their diet. Three major studies tallied 464 available plant species in the study areas, of which 88 occurred in the diets of Western Hoolock Gibbons. In north-eastern India, they are an important disperser of seeds for large and small fruit-bearing trees.
Breeding. Mating of the Western Hoolock Gibbon occurs during the wet season (monsoon) in May-June, and birth peaks occur during the dry season in November—February. Offspring are weaned at about two years old and are considered juvenile until about four years old and subadults between four and six years old. Interbirth intervals are about three years.
Activity patterns. In Bangladesh, Western Hoolock Gibbons spend their days feeding (30-8%), foraging (25-8%), resting (27-5%), and traveling (7-4%), besides calling and engaging in territorial behavior and play. In India, play and grooming activities contribute less than 10% oftheir daily activities. They rest and play more in the longer days of summer. Gibbons are active for 8-10 hours, starting at dawn or in the early morning, waking earlier in summer than winter. Pairs of Western Hoolock Gibbons call in the morning before leaving their sleeping sites on most but not all days and sometimes in the afternoon before retiring. They alternate their calls as a “double solo” rather than producing duets. Feeding dominates the morning hours and rest in the early afternoon. Activity ends usually several hours before sunset, possibly to avoid competing with other primates at their feeding trees. Preferred sleeping sites are emergenttrees, often those infested with epiphytes; mid-canopy trees are less preferred. A female and her infant sleep together, generally with the adult male; older offspring sleep separately.
Movements, Home range and Social organization. Western Hoolock Gibbons live in family groups of 2-6 individuals (usually about three), consisting of an adult pair, juveniles, and infants. Females dominate males. In Bangladesh, their home ranges are 8-63 ha, while home ranges in India can be 200-400 ha, probably based on the size of the habitat fragments. They travel 300-1800 m/day. Scarcer food and more widely dispersed food sources are probably the reason for larger home ranges in India.
Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List. The Western Hoolock Gibbon is legally protected in Bangladesh, India, and Myanmar. It is threatened by habitat loss and hunting for food and traditional Asian medicine. In Bangladesh, there is an estimated population of only 300 individuals in highly fragmented pockets of suitable habitat, while in north-eastern India, there are 2200-2600 individuals. More than 50% of the Western Hoolock Gibbons in India is in isolated, small, and unsustainable subpopulations, often ofjust one or two groups. Across India and Bangladesh, habitat quality is rapidly declining, even where the forest is left standing; they suffer the loss of their preferred food trees and adequate sleeping sites, and the remaining forest structure and the broken canopy do not allow for brachiation. The degradation and destruction of their forest habitats results from the collection of firewood, timber extraction, plantations for the pulp industry, invasion of exotic plant species, crop cultivation, erosion, and disturbance of undergrowth, road construction, and urbanization. Unplanned intensive tourism, hunting, army training, natural gas extraction, slash-and-burn agriculture (“jhum” cultivation), and intensive commercial agriculture, such as tea plantations, comprise major threats. Commercial and subsistence hunting for food by hill tribes is particularly severe in Nagaland in far north-eastern India. Even when not hunted, people compete for food and cut down preferred fruit trees for timber, degrading the remaining forest patches. Namdapha National Park in the Changlang district of Arunachal Pradesh has the largest contiguous stretch of protected forest in India and is a stronghold for the Western Hoolock Gibbon. They also occur in Lawachara National Park and Chunati and West Bhanugach wildlife sanctuaries in Bangladesh and Balphakram, Nokrek, Namdapha, Dibru-Saikhowa, Intanki, Kaziranga, and Murlen national parks and Bherjan, Borajan, Dampa, Garampani, Hoollongapar Gibbon, Gumti, Kamlang, Khawnglung, Nengpui, Nongkhyllem, Phawangpui, Sepahijala, Siju, and Trishna wildlife sanctuaries in India.
Bibliography. Ahsan (1993, 1994, 1995), Alfred (1992), Alfred & Sati (1990, 1991, 1994), Biswas (1970), Brockelman, Molur & Geissmann (2008), Bujarbarua & Das (2001), Chetry et al. (2007), Chivers (2001), Choudhury (1987, 1989b, 1990, 1991, 1996, 2000, 2001, 2006), Dam (2006), Das (2002), Das, Biswas et al. (2003), Das, Feeroz et al. (2003), Feeroz & Islam (1992), Gittins & Tilson (1984), Groves (1967, 1972, 2001), Gupta (2005), Haimoff (1985b), Hasan et al. (2007), Hazarika & Gupta (2005), Islam & Feeroz (1992), Kakati (2004), Kakati et al. (2009), King et al. (1995), McCann (1933), Molur et al. (2005), Mootnick (2006), Mootnick & Groves (2005), Mukherjee (1986), Mukherjee et al. (1986, 1988, 1991/1992, 1992), Muzaffar et al. (2007), Prouty et al. (1983a, 1983b), Sati & Alfred (2001, 2002), Srivastava (2006a), Srivastava, Das et al. (2001), Takacs et al. (2005), Tilson (1979), Walker (2005), Walker et al. (2007).
description: Published as part of Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Hylobatidae, pp. 778-791 in Handbook of the Mammals of the World – Volume 3 Primates, Barcelona :Lynx Edicions on page 779, DOI: 10.5281/zenodo.6727957