Hoolock gibbon


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Suborder: Haplorrhini
Infraorder: Simiiformes
Superfamily: Hominoidea
Family: Hylobatidae
Genus: Hoolock
Species: H. hoolock, H. leuconedys

Other names: hoolock gibbon, white-browed gibbon; tooboung, myouk umaigyall (Arakanese); hoolock (French); uluk (Hindi); gibón hulock (Spanish); holockgibbon, holok, hulock (Swedish); wu-wa (Thai); H. hoolock: western hoolock; H. leuconedys: eastern hoolock.

Conservation status:
Endangered (H. hoolock), Vulnerable (H. leuconedys)

Life span: 30 years (captive)
Total population: <35000 (H. hoolock)
Regions: India, Bangladesh, Burma, China
Gestation: 6 to 8 months
Height: 81.2 cm (M & F)
Weight: 6.9 kg (M), 6.1 kg (F)

The taxonomy of the hoolock gibbon has recently been significantly revised. Hoolock gibbons have been placed within their own genus, Hoolock, as well as split into two discrete species, the western hoolock gibbon (H. hoolock) and the eastern hoolock (H. leuconedys) (Mootnick & Groves 2005). However, in many publications, the two species are only considered distinct at the subspecific level. Further, the vast majority of the available published literature is on the western hoolock, but due to presumable similarities between the species, both are included here.


Hoolock gibbon

The hoolock gibbon is tailless like all other apes (Groves 1972; Choudhury 1991). However, the species possesses a tuft of hair in the anogenital region (Marshall & Sugardjito 1986; Choudhury 1991; Mootnick 2006). Sexual dichromatism is seen between males and females but sexual dimorphism is not pronounced (Groves 1972; Jenkins 1990; Choudhury 1991; Alfred 1992). Both sexes have thick and shaggy hair with long limbs (Roonwal & Mohnot 1977; Choudhury 1991). Males are black or blackish, with a white strip above their eyes which curves up at either end (Choudhury 1991; Das et al. 2006; Mootnick 2006). The face of both sexes is black (Choudhury 1991). In contrast to the males, adult females are lighter, usually ranging from buff and pale to various shades of tan with some brown, grey and yellowish coloration (Roonwal & Mohnot 1977; Choudhury 1991; Islam & Feeroz 1992; Mootnick 2006).

Between the species, there are some morphological differences, predominantly between males with females significantly harder to distinguish visually (Jenkins 1990). In H. hoolock, males are black, with a white unibrow (mono-brow) and a black genital tuft (around 5 cm (2.0 in) long) (Groves 1972; Jenkins 1990; Mootnick 2006). H. leuconedys males have two distinct white eyebrows and a silver or white genital tuft (around 7.5 cm (3.0 in)) (Groves 1972; Jenkins 1990; Das et al. 2006; Mootnick 2006).

The average height of a hoolock gibbon is 81.2 cm (32.0 in) (A. Mootnick pers comm.). Females weigh around 6.1 kg (13.4 lb) while males weigh around 6.9 kg (15.2 lb) (Leutenegger & Cheverud 1982).

Hoolock gibbon

Hoolock gibbons are almost entirely arboreal, coming to the ground only in exceptional circumstances. Movement is primarily through brachiation (70-80% of movement), leaping, climbing and jumping (16-25%) and acrobatics or bipedal walking (4-5%) (Alfred 1992; Islam & Feeroz 1992; Sati & Alfred 2002). When moving bipedally they usually travel for less than a minute and they will move quadrupedally on rare occasions (Islam & Feeroz 1992). Any bipedal movement that does occur is typically unsteady and awkward (Candler 1904; Alfred 1992). Such bipedality can occur both arboreally or terrestrially with and without the animal using its arms for support. Terrestrial bipedality usually only occurs when trees are too far apart to leap between (Jindal & Sharma 1984; Alfred 1992). Hoolock gibbons feed while either sitting or suspended from a support, depending on the food (Sati & Alfred 2002). During the morning in the winter, hoolock gibbons will “sunbathe” in high branches exposing their backs to the sun for several minutes at a time (Tilson 1979; Choudhury 1996). In general, most of the daily activities occur between 6 and 20 m (19.7 and 65.6 ft) above ground level (feeding, movement, resting and calling) except social activities, which normally occur between 5 and 27m (16.4 and 88.6 m) (Hasan et al. 2007).

Hoolock gibbons have lived to be as old as an estimated 40 years in a captive setting (Weigl 2005).


Hoolock hoolock | Hoolock leuconedys

In general, starting in the east and moving roughly westerly, hoolock gibbons are found only in China, Myanmar, northeastern India, and Bangladesh (Mukherjee 1984; Yang et al. 1987; Ma et al. 1988; Mukherjee et al. 1992). Hoolock gibbons are the only ape present in India and within China, hoolock gibbons are found only in the western Yunnan province (Yang et al. 1987; Ma et al. 1988; Mukherjee et al. 1992; Das et al. 2006). In addition, they are only found west of the Salween River in Myanmar (Groves 1972). In eastern India, the hoolock is restricted to the states of Assam, Arunachal, Pradesh, Nagaland, Manipur, Mizoram, Tripura, and Meghalaya. Thus, in general they are found in India south and east of the Brahmaputra, Lohit, and Dibang Rivers (Groves 1972; Choudhury 1987; 2006). Within Bangladesh, hoolock gibbons are only found in the southeast and northeast (Feeroz et al. 1995).

The distributions of the two species are demarcated by the Chindwin and Irrawaddy Rivers in Myanmar, with H. leuconedys occurring to the east and H. hoolock to the west of the watercourses (Groves 1967; Ma et al. 1988). The distribution of H. leuconedys continues east as far as the Salween River in Myanmar (Groves 1972). However, there are recent reports of hoolock gibbons close in appearance to H. leuconedys reported in the Lohit district of Arunachal Pradesh, India, the most easterly district in India which may require revision of the current geographical division between species (Das et al. 2006).

It is important to remember however, that the distribution is not continuous and in many cases is quite fragmented (Choudhury 1991). There are estimated to be roughly 200 western hoolock gibbons left in the wild in Bangladesh (Biswas et al. 2003; Molur et al. 2005; Walker et al. 2007) and there is no published information on the status of western hoolock gibbons in Myanmar (Kakati 2006; Walker et al. 2007).


Hoolock gibbons are exclusively forest-dwelling and depend on a contiguous canopy. They are found in broad-leaved, moist deciduous forest; mixed evergreen/deciduous forest with tall deciduous trees and an evergreen understory; sub-tropical broadleaf forests, from mountainous, hill, valley, slope and lowland forests to wet evergreen and semi-evergreen forests often consisting of interspersed trees and bamboos as well as various conditions of forest, including primary, secondary, and regenerating (Khan & Ahsan 1986; Mukherjee 1986; Choudhury 1990; 1991; Islam & Feeroz 1992; Mukherjee et al. 1991-1992; 1992; Lan 1994; Choudhury 1996; 2000; Ahsan 2001; Sati & Alfred 2002; Das et al. 2003; Choudhury 2006; Kakati 2006; Srivastava 2006). The best habitats have continual canopy of tall trees with thick undergrowth (Mukherjee et al. 1991-1992; Bai et al. 2007). Typical tree species found in hoolock habitats include Mangifera, Bixa, Dipterocarpus, Zyzygium, Protium, Entada, Lagerstoemia, Shorea, Albizzia, Artocarpus, and Ficus (Mukherjee 1986; Muzaffar et al. 2007). Hoolock gibbons are found at altitudes under 50 m and up to and above 2500 m (Choudhury 2006).

In general, hoolock gibbon habitats are tropical with wet, hot summers with monsoon rains and dry cool winters. Annual rainfall is usually between 130 and 400 cm (51.2 and 157.5 in) (Choudhury 1991). For example, in Assam, India, the annual temperature usually ranges between 7°C (44.6°F) and 32°C (89.6°F) (Choudhury 2000).


Hoolock gibbons are primarily omnnivorous, consuming, in some habitats, over 100 species of plants although sometimes the number of species is far lower (Alfred 1992; Islam & Feeroz 1992; Ahsan 2001). The species and number of food species can vary greatly between study site (based partially on availability and density) and they also consume some prey items, predominantly invertebrates but also birds’ eggs (Mukherjee 1986; Alfred 1992; Ahsan 2001). In the diet, figs dominate and fruits are very important however lianas, flowers, shoots, petioles, exudates, nectar, and other plant foods, including lichens, are also consumed (Islam & Feeroz 1992; Ahsan 2001; Bujarbarua & Das 2001). In one study, when expressed as a percentage, fruits comprised 65% of the diet (60% of this is figs), buds, young shoots, and leaves 25%, and flowers and insect 10% (Alfred 1992). In most studies, proportions were roughly similar, with fruit, especially figs, predominating, followed by other plant parts and to a lesser extent, insects (Tilson 1979; Gittins & Tilson 1984; Ahsan 1992; Islam & Feeroz 1992; Feeroz et al. 1994; Ahsan 2001; Hazarika & Gupta 2005). However, sometimes leaves are nearly as important as fruit in the diet (Hazarika & Gupta 2005).

While variable between study sites and study groups, in Bangladesh, hoolock gibbons spend their days feeding (30.8%), foraging (25.8%), resting (27.5%), traveling (7.4%), with the rest of the day spent in other activities, including calling, territorial behavior, and play (Ahsan 2001). Although variable, in general between study sites, feeding, moving and resting activities predominate followed by other activities (Alfred 1992; Feeroz & Islam 1992; Islam & Feeroz 1992; Gupta 1994; Ahsan 2001; Hazarika & Gupta 2005). Social activities including play and grooming take up less than 10% of the day (Gupta et al. 2005).

Diurnal hoolock gibbons are usually active, starting at dawn or in the early morning, for 8-10 hours each day (Mukhergee 1986; Feeroz & Islam 1992; Gupta et al. 2005). Hoolock gibbons start activity early in the morning and they awake earlier in the summer than in the winter (Gittins & Tilson 1984; Alfred 1992; Ahsan 2001). As they leave their sleeping sites, hoolock gibbons usually defecate and urinate (Ahsan 2001). Feeding peaks during the morning hours while movement peaks right before hoolock gibbons move to their sleeping trees at the end of the day with a second smaller peak in the morning (Islam & Feeroz 1992; Ahsan 2001). Resting activity peaks in the early afternoon (Ahsan 2001). Calling occurs only before noon, and then usually in the earlier morning (Islam & Feeroz 1992; Ahsan 2001). The end of the activity period is usually several hours before sunset possibly to avoid feeding overlap with sympatric monkeys (Ahsan 2001; Gupta et al. 2005). In the summer when the days are longer, more resting and social behavior is seen (Gittins & Tilson 1984).

The home range of hoolock gibbons varies with study site, and can range between 0.15 and 0.30 km² (0.06 and 0.1 mi²) up to 3-4 km² (1.2-1.5 mi²), with some intermediate sizes as well as some overlap with neighboring groups (Tilson 1979; Gittins & Tilson 1984; Alfred 1992; Islam & Feeroz 1992; Choudhury 1996; Ahsan 2001; Gupta et al. 2005). Average day ranges can vary between 600 m (1968.5 ft) and around 1350 m (4429.1 ft) but single day ranges can be less than 300 m (984.3 ft) and more than 3000 m (9842.5 ft) with the highest day ranges occurring during the summer (Mukherjee 1986; Islam & Feeroz 1992; Ahsan 2001; Gupta et al. 2005).

In captivity and in the wild, hoolock gibbons generally sleep with the knees tucked up into the chest and the arms around them in a hunched position (McCann 1933; Jindal & Sharma 1982). In the wild, sleeping trees are usually taller than those nearby and are normally located on slopes or hilltops. Usually, hoolock gibbon groups do not all sleep together in the same tree but instead in several nearby trees (Ahsan 2001).

Several species of bird (magpies, drongos, and laughing thrushes), sometimes chase hoolock gibbons when they are in food trees, with drongos being more aggressive, continuing confrontations until hoolock gibbons leave (Islam & Feeroz 1992). Hoolock gibbons compete for food with the Malayan giant squirrel and do not allow them to remain nearby. Primate species with which hoolock gibbons may be sympatric include Phayre’s leaf monkeys (Trachypithecus phayrei), capped langurs (T. pileatus), slow loris (Nycticebus coucang), rhesus macaques (Macaca mulatta), Assamese macaques (M. assamensis), pigtail macaques (M. nemestrina) and stump-tailed macaques (M. arctoides) (Mukherjee et al. 1992). When in contact with other sympatric primates, langurs, lorises and macaques are usually tolerated by hoolock gibbons although agonism can occur (Mukherjee 1986; Islam & Feeroz 1992). Pigtailed macaques are often avoided because of the large group sizes of that species (Feeroz & Islam 1992). The general ability of hoolock gibbons to coexist with sympatric primates as well as other species with which it has food overlap is partially attributable to differences in daily activity patterns (Islam & Feeroz 1992).

Potential predators of hoolock gibbons include eagles, vultures, leopards, and pythons (Gupta et al. 2005).

Content last modified: August 13, 2008

Written by Kurt Gron. Reviewed by Alan Mootnick.

Cite this page as:
Gron KJ. 2008 August 13. Primate Factsheets: Hoolock gibbon (Hoolock) Taxonomy, Morphology, & Ecology . <http://pin.primate.wisc.edu/factsheets/entry/hoolock_gibbon/taxon>. Accessed 2020 July 22.


Hoolock gibbon group size averages around 3 individuals, and typically ranges from around 2-6 individuals however solitary individuals are sometimes seen (McCann 1933; Tilson 1979; Gittins & Tilson 1984; Siddiqi 1986; Alfred & Sati 1990; Choudhury 1990; 1991; Mukherjee et al. 1991-1992; Alfred 1992; Feeroz & Islam 1992; Islam & Feeroz 1992; Gupta 1994; Choudhury 1996; Ahsan 2001; Chetry 2002; Das et al. 2003; Gupta et al. 2005; Kakati 2006; Das et al. 2006). Groups with more than one adult male or more than one breeding adult female have been known to occur, as have all-male groups (Choudhury 1991; Mukherjee et al. 1991-1992; Ahsan 1995; Choudhury 1996). The majority of groups consist of a serially monogamous mated pair of adults and usually one or several immature individuals (Tilson 1979; Gittins & Tilson 1984; Alfred 1992; Choudhury 1996; Ahsan 2001). Over the course of the day, all group members on average are no more than 12.5 m (41.0 ft) from one another. During travel, the adult of either sex can lead the group but travel is usually single-file (Mukherjee 1986; Islam & Feeroz 1992; Ahsan 2001).

Territories are defended through territorial disputes usually led by the group adult male. Such disputes normally occur in areas of overlap with the home ranges of other hoolock gibbon groups (Islam & Feeroz 1992). Territorial boundaries are maintained through vocalization bouts, the visiting of all parts of the territory often, disputes with neighboring groups, and the progressive expulsion of offspring from the territory as they age (Ahsan 2001). Intergroup encounters occur often and usually consist of vocalization and counter-vocalization, with males chasing one another, but typically not violently (Gittins & Tilson 1984; Gupta et al. 2005). Aside from vocalizing during territorial disputes, females usually do not participate otherwise and remain peripheral (Gittins & Tilson 1984). Such overlap zones between home ranges have been called territorial boundaries between hoolock groups (Tilson 1979). Vocalizations are likely important in the maintenance of territorial boundaries and Solitary individuals do not maintain discrete territories and have been seen moving between the established territories of other hoolock groups (Tilson 1979). Intergroup encounters can exceed one hour in length (Gittins & Tilson 1984).

Grooming is often seen during group social activities and serves in the maintenance of social bonds, reducing aggression, and for hygienic purposes. Grooming frequency increases between February and May when the weather is warmer and is usually started and performed by the adult male of the group (Ahsan 2001). The typical grooming bout involves one individual grooming the head and back of the other (Islam & Feeroz 1992). However, grooming frequency is usually quite low overall (Mukherjee 1986). Self-grooming is also seen often (Alfred 1992). Play usually occurs between immature individuals but occasionally one of the adults will play with immature members of the group (Alfred 1992; Sati & Alfred 2001). Play is one of the most common social behaviors (Sati & Alfred 2001).

The formation of a new hoolock gibbon group can occur in several ways; the pairing of a brother and sister, the pairing of a father and daughter, emigration and subsequent re-mating, or dispersed subadult pair formation (Ahsan 2001).

Hoolock gibbons of both sexes emigrate from their natal groups when they become mature adults (Gupta et al. 2005).


Hoolock gibbons are typically monogamous, living in mating pairs with offspring (Siddiqi 1986; Choudhury 1991; Gupta et al. 2005). Mating occurs during the summer rainy season with births during the winter, usually between September and January (McCann 1933; Alfred 1992; Tilson 1979; Choudhury 1990; Alfred 1992; Ahsan 2001). Regardless, in some studies copulation occurs nearly year-round and summer births have been seen (Alfred 1992; Ahsan 2001). Copulation usually occurs in the morning, lasts on average around half a minute and is usually in a ventro-ventral position (Islam & Feeroz 1992; Ahsan 2001; Sati & Alfred 2001). Newborns are almost always seen only between November-January (Alfred & Sati 1990).

Gestation is between 6 and 8 months (Sati & Alfred 2001; Ahsan 2001). The inter-birth interval is estimated at around two years, although some authors place it higher, around 3-4 years (Alfred & Sati 1990; Ahsan 1994 cited in Ahsan 2001). The female menstrual cycle lasts on average 27.8 days (Matthews 1946). Sexual maturity in females is reached around 5-8 years of age, and is shown by the fading of the black coat to the paler pelage of adult females (Tilson 1979; Islam & Feeroz 1992).


Births are singletons (Choudhury 1990). Neonatal infants are almost completely white, pale-grey whitish-yellow, or whitish-yellow with black hands, feet, and face (Choudhury 1991; Ahsan 2004; Mootnick 2006). Body length of the infant is normally between 20 and 35 cm (7.9 and 13.8 in) (Alfred 1992). By a year old, the pelage darkens to mostly brown/black and the coloration becomes progressively darker until 24 months of age, when they are completely black with distinct eyebrows (Ahsan 2004). This process occurs in both sexes and later, females experience yet another color change when they attain the adult female pelage coloration around 5-8 years old, at sexual maturity (Tilson 1979; Islam & Feeroz 1992).

For the first two months of life in the wild, infant hoolock gibbons predominantly cling to the ventrum of their mother, including the chest and belly (Alfred 1992; Islam & Feeroz 1992; Ahsan 2004). The infant hoolock gibbon first ventures away from its mother at around 6 months of age and by 17 months of age, a degree of independence is seen, with the infant playing with others, but always within several meters of the mother (Ahsan 2004). By 21 months old leaping and jumping is first seen and by 22 months old such locomotor behaviors are more adept. Suckling can occur through 26 months of age, as does sleeping with the mother (Ahsan 2004). In fact, the infant will persist in sleeping with the mother until the birth of a new infant (Sati & Alfred 2001).

Infanticide by an adult male has been observed in hoolock gibbons (Alfred & Sati 1991).


Hoolock gibbon

The vocalizations of hoolock gibbons are not sexually dimorphic, meaning that there are no sex-specific vocalizations, a fact that sets them apart from all other species of gibbons (Haimoff 1985; Choudhury 1989; 1991; Geissmann 1995). Calls can usually be heard up to a kilometer away (Choudhury 1989). Types of call include female growling, hoos, great calls, semi-great calls, repair and aborted calls, organizing sequences, alarm calls, cries, whimpers and squeals (Ahsan 2001). Infants have characteristic distress calls (Alfred 1992). Other vocalizations consist of growls and exhalation sounds, and probably function in intra-group communication (Alfred 1992). Males may call alone before sunrise (Gupta et al. 2005).

Usually, calls are uttered during loud and complex call bouts or duets, which make up almost 90% of all vocalization and occur mostly in the morning, usually lasting up to 20 minutes (Gittins & Tilson 1984; Alfred & Sati 1986; Choudhury 1989; 1991; Alfred 1992; Ahsan 2001; Gupta et al. 2005). There are three main call bout types; the great call, organizing sequences, and alarm calls (Ahsan 2001). Sometimes juveniles of either sex may join in a call bout (Choudhury 1989). Singing does not occur every day, but when it does occur, usually occurs from high areas such as tall, large, peripheral trees on hilly terrain and usually near or on overlap of home ranges (Choudhury 1991; Ahsan 2001; Hasan et al. 2007). The majority of calls are produced near the edges of the territory or outside of it (Islam & Feeroz 1992). Further, it is possible for call bouts to occur more than once a day (Gittins & Tilson 1984; Choudhury 1989). Call bouts can be elicited in a number of ways. These include the singing of a nearby group at the territorial edge, during a territorial conflict, in food competition, the singing of a neighbor group not in an overlapping territory, vocalizations of other animals (especially birds), and train whistles (Ahsan 2001). Once calling commences, call bouts are often responded to by other hoolock gibbon groups throughout the forest (Alfred 1992). Sometimes, neighboring groups only start calling after the adjacent group ceases (Gittins & Tilson 1984). Call bouts serve to initiate territorial disputes which ensue if the calling does not keep neighboring groups apart (Islam & Feeroz 1992). During a bout, calling may be continuous or discontinuous (Islam & Feeroz 1992). As a call bout continues, the female great call vocalizations accelerate, with the male joining halfway through the great call (Geissmann 1995). Temperature and weather also affect the frequency and occurrence of hoolock gibbon call bouts (Ahsan 2001).

Functions of calling in hoolock gibbons include the maintenance of the pair-bond, reinforcement of social ties, mate attraction and defense, mate solicitation, and in territoriality reinforcement and defense (Islam & Feeroz 1992; Ahsan 2001).

Hoolock gibbons possess skin glands which may have some function in olfactory communication (Geissmann & Hulftegger 1992).

Content last modified: August 13, 2008

Written by Kurt Gron. Reviewed by Alan Mootnick.

Cite this page as:
Gron KJ. 2008 August 13. Primate Factsheets: Hoolock gibbon (Hoolock) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/hoolock_gibbon/behav>. Accessed 2020 July 22.




CITES: Appendix I (What is CITES?)
IUCN Red List: H. hoolock: EN; H. leuconedys: VU (What is Red List?)
Key: EN = Endangered, VU = Vulnerable
(Click on species name to see IUCN Red List entry, including detailed status assessment information.)

Hoolock gibbon

In general, hoolocks are extremely threatened with the western variety, H. hoolock listed as one of the World’s 25 Most Endangered Primates, 2006-2008. It is said that the species’ survival is entirely contingent on human action and their numbers, over 100,000 in the 1970’s, have seen a dramatic reduction (Walker et al. 2007). Populations in Bangladesh number a combine total of around 200 individuals, and even these numbers are in very small and isolated populations with low long-term viability (Biswas et al. 2003; Molur et al. 2005; Walker et al. 2007). The total population in northeast India is between 1700 and 2200 individuals (Choudbury 2007). The best hope for the western hoolock gibbon is in Myanmar where there is around 50,000 km² of forest in the Rakhine Yoma region, with 175,500 ha managed by the Nature and Wildlife Conservation Division of the Forest Department of Myanmar (Walker et al. 2007). At present, it seems that the eastern hoolock gibbon situation in Myanmar is more secure based on preliminary surveys (Walker et al. 2007) with a rough estimate of 30,000 east of the Chindwin River (A Mootnick & W Brockelman pers comm.). However, in China, the numbers of eastern hoolocks are estimated at less than 150 individuals (Zhang 1998). All told, unless habitat loss is stopped, chances are high that the western hoolock will become extinct within 50 years (Walker 2005).

Hoolock gibbons are protected by law in India making it illegal to kill or capture the species, but their conservation has been less a priority than that for other large mammals in the nation (Molur et al. 2005; Choudhury 2006). In addition, a reliance on forest resources is exacerbated by human population pressure, immigration and bad economic conditions (Das 2002-2003; Walker et al. 2007). In fact, in some areas, everyone living in proximity to hoolock gibbon habitat is reliant on the forest for their livelihood (Mukherjee et al. 1988). Compounding the problem, authorities have little power to curtail illegal forest use (Srivastava et al. 2001). Essentially, hoolock gibbons are seriously threatened ultimately due to some of the highest human growth rates in the world which result in habitat degradation (Gupta et al. 2005).

The species are especially vulnerable to habitat degradation and destruction due to their preferences for pristine forests with contiguous canopy. As a result, they have a hard time living in secondary forests and discontinuity of forests is a major problem for the species (Mukherjee 1986; Mukherjee et al. 1991-1992; Kakati 2006; Osterberg 2007).


Threat: Human-Induced Habitat Loss and Degradation

As is the case with most primates, the primary threat to the hoolock is habitat destruction, degradation, and fragmentation (Das et al. 2003; Dam 2006). Reasons for habitat destruction and degradation include, but are not limited to, logging (both legal and illegal), bamboo harvesting for paper manufacture as well as for domestic uses, tree bark extraction, road construction, monoculture tree plantations, fuel wood extraction, coal mining, stone quarrying, livestock grazing, and agriculture, including tea and rice cultivation (Mootnick et al. 1987; Choudhury 1996; Ahsan 2001; Das 2002-2003; Das et al. 2003; Choudhury 2006; Kakati 2006; Osterberg 2007). While local-level timber extraction for fuel may not profoundly affect the forest, commercial-level extraction most assuredly does, resulting in profound forest degradation (Ahsan 2001). Other factors precipitating hoolock habitat destruction include the conversion of rainforest to plantations of teak, hydro-electric dam projects, high-tension electric wires, roads, railways, oil drilling, irrigation, and encroaching human settlement (Choudhury 1990; 1996; Dam 2002-2003; Das et al. 2006). Betel Leaf (a south Asian spice) cultivation also causes primates to become absent from potential habitat, with methods used in the growing of the plant rendering forests unsuitable for hoolock gibbons (Ahsan 2001). Shifting cultivation (“Jhum”) is a common method of slash-and-burn agriculture in eastern India in which new fields are cleared each year, resulting in rapid deforestation (Mukherjee et al. 1992; Gupta 1994). It is agricultural methods of this type that are the primary reason for the fragmentation degradation, and clearing of hoolock habitat in some areas (Alfred & Sati 1990; Choudhury 1996).

Threat: Invasive Alien Species

Hoolock gibbons are occasionally killed by domestic dogs when they come to the ground to cross gaps in discontinuous degraded forest (Choudhury 2000).

Threat: Harvesting (hunting/gathering)

Hoolock gibbons are hunted for food by several ethnic groups in northeast India, utilizing snares, muzzle-loading and automatic firearms (Mukherjee et al. 1992; Choudhury 1990; 1991; 1996; 2006). Further, hunting and poaching by both local and non-local individuals are significant threats to populations (Mootnick et al. 1987; Choudhury 1991). Hoolock gibbons are also hunted for folk medicine (Walker et al. 2007). However, in some areas, such as parts of Arunachal Pradesh, India, hoolock gibbons are not hunted, often for religious reasons and in fact, sightings on the ground are sometimes considered to be bad omens (Choudhury 2000; Ahsan 2001). Gibbons are also sometimes hunted for commercial sale and hoolock meat has been found for sale in markets. Further, the species are sometimes taken for trade and sub-adults are sometimes taken as pets (Choudhury 2006; Walker et al. 2007).

Threat: Human Disturbance

Tourism has the potential to degrade hoolock gibbon habitat due to visitor littering, disturbance of the animals, and collateral pollution (Ahsan 2001). Also, humans sometimes directly come into food competition with hoolock gibbons, as some foods are consumed by both, especially fruits (Ahsan 2001).

Potential Solutions

One solution may be to combine action by the government, industry, non-government organizations, and communities in Bangladesh and northeast India to protect hoolock gibbons from enduring further forest fragmentation. Another potential solution may include offering economic incentives to landowners to contribute land to create corridors between fragmented forests and larger forests (Kakati 2006).





Content last modified: August 13, 2008

Written by Kurt Gron. Reviewed by Alan Mootnick.

Cite this page as:
Gron KJ. 2008 August 13. Primate Factsheets: Hoolock gibbon (Hoolock) Conservation . <http://pin.primate.wisc.edu/factsheets/entry/hoolock_gibbon/cons>. Accessed 2020 July 22.


The following references were used in the writing of this factsheet. To find current references for Hoolock, search PrimateLit.


Ahsan MF. 1994. Behavioural ecology of the hoolock gibbon (Hylobates hoolock) in Bangladesh. PhD dissertation, University of Cambridge, Cambridge (UK).

Ahsan MF. 1992. Feeding ecology of the primates of Bangladesh. In: Thierry B, Anderson JR, Roeder JJ, Herrenschmidt N, editors. Current primatology, volume I: ecology and evolution. Strasbourg(FR):Universite Louis Pasteur. p 79-86.

Ahsan F. 1995. Fighting between two females for a male in the hoolock gibbon. Intl J Primatol 16(5):731-7.

Ahsan MF. 2004. Infant behaviour and development in hoolock gibbon (Bunopithecus hoolock hoolock). Zoos’ Print J 19(4):1435-6.

Ahsan MF. 2001. Socio-ecology of the hoolock gibbon (Hylobates hoolock) in two forests of Bangladesh. Brookfield Zoo, compiler. The apes: challenges for the 21st century: conference proceedings, May 10-13, 2000. Brookfield (IL):Brookfield Zoo. p 286-99.

Alfred JRB, Sati JP. 1986. The gibbons with special reference to Hylobates hoolock. In: Majupuria TC, editor. Wildlife wealth of India (resources & management). Bangkok (TH): Tecpress Service, LP. p 384-90.

Alfred JRB. 1992. The hoolock gibbon: Hylobates hoolock. Prim Rep 34:65-9.

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Content last modified: August 13, 2008


Hoolock hoolock
Photo: Alan Mootnick
Hoolock hoolock
Photo: Alan Mootnick

Hoolock leuconedys
Photo: Gabriela Skollar/Gibbon Conservation Center
Hoolock leuconedys
Photo: Gabriela Skollar/Gibbon Conservation Center

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