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Overview

Distribution

Range Description

This species is found in eastern Bangladesh, northeastern India (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura), and northwestern Myanmar (west of the Chindwin River). It might possibly occur in China (extreme southeastern Tibet). The distribution in India is restricted to points south of the Brahmaputra and east of the Dibang (Dingba Qu) Rivers (Choudhury 2001). Animals that once were common in the plains of Arunachal Pradesh (northeasternmost India) before that habitat was cultivated for agriculture and tea are not so anymore (Islam and Feeroz 1992).

The boundary between the two species of Hoolock is the Chindwin River, which flows into the Ayerawady (Irrawady) River. At the headwaters in the north there is a hybrid zone or cline between the two species (since they are almost certainly not reproductively isolated). Das et al. (2006) reported the discovery of a population of H. leuconedys in Arunachal Pradesh, northeast India, which has traditionally been considered to be part of the range of H. hoolock.
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Geographic Range

Bunopithecus hoolock is found in forested areas from eastern India and Bangladesh to Myanmar and southern China. Geographically, the natural range pf Hoolock gibbons extends east to the Salween River and west to the Brahmaputra River. Of all gibbon species, their range extends the farthest north and east (Wolfheim, 1983).

Biogeographic Regions: oriental (Native )

  • Wolfheim, J. 1983. Primates of the World. Seattle, WA: University of Washington Press.
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Physical Description

Morphology

Physical Description

Bunopithecus hoolock is the second largest of the gibbons following siamangs. They weigh between 6 and 8 kg. Hoolock gibbons are characterized by longer hair, curved white brow streaks, and faintly triangular-shaped head. This species is dichromatic: adult males are completely black, whereas adult females are dark brown with black on the neck, chest, and facial areas. In some subpopulations, males have more defined brow streaks than in others. Males may also have a white preputial tuft, and may show white on their chins and cheeks. Some females have lighter pelage on their hands and feet (Chivers and Gittins, 1978). Unique among gibbon species, B. hoolock has only 38 chromosomes, compared to 44 in other members of its subgenus (Nowak, 1999).

Range mass: 6 to 7 kg.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes colored or patterned differently; male more colorful

  • Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.
  • Chivers, D., S. Gitins. 1978. Diagnostic features of gibbon species. International Zoo Yearbook, 18: 157-173.
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
This species is a forest-dweller that, depending on its locale, inhabits tropical evergreen rainforests, tropical evergreen and semi-evergreen forests, tropical mixed deciduous forests, and subtropical broadleaf hill forests. It has also been noted in bamboo “brakes” and hollock (Terminalia myriocarpa) and ajhar (Largerstroemia flosreginae) plantations. One gibbon pair in the Borajan Reserved Forest (north-east India) was observed to habitually descend from the trees to move over scrub and short bamboo especially while trying to reach the isolated food trees inside a village. This pair was found sleeping at heights of 0 m or less in bamboo clumps (Kakati 1997). Although gibbons may be moving through, or sleeping in, bamboo forest or plantations, they cannot survive in monocultures (W. Brockleman pers. comm.). Additionally, the species has been observed in two plains forest locations (Choudhury 1991). Its preferred habitat, however, is dense evergreen and semi-evergreen forests (Choudhury 2001). It has been recorded at altitudes of up to 2,500 m in Manipur, northeast India (Choudhury 2001).

Home ranges in most populations range from 8-63 ha (Ahsan 2001; Alfred 1992; Alfred and Sati 1986, 1990; Feeroz and Islam 1992; Gittins and Tilson 1984; Islam and Feeroz 1992; Kakati 2004; Mukherjee 1986; Tilson 1979), but unusually large home ranges of 200-400 ha were reported from Tripura and Arunachal Pradesh, northeast India (Mukherjee 1982; Mukherjee et al. 1988). The western hoolock is a frugivorous species, with ripe fruits composing a majority of its diet (Ahsan 2001; Alfred and Sati 1986, 1994; Feeroz and Islam 1992; Islam and Feeroz 1992; Kakati 1997; Tilson 1979). A dominantly folivorous diet was reported during studies carried out in Assam’s Borajan Reserved Forest, and in Tripura (Kakati 1997; Mukherjee 1986), and gibbons living in small forest fragments were observed to experience a period of almost total lack of fruit in their diet at the end of the dry season (Kakati, 2004). Low fruit availability may contribute to the relatively large home range sizes of some populations. In northeast India, the hoolock gibbon is recognized as being an important disperser of undigested seeds from large and small fruit-bearing trees (Das 2003).

Systems
  • Terrestrial
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This species is found in thick evergreen, mixed evergreen, and scrub forest throughout its natural range. Hoolock gibbons usually prefer undisturbed forested areas and are found at elevations ranging from 152 to 1,370 m (Wolfheim, 1983).

Range elevation: 152 to 1,370 m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: forest ; rainforest ; scrub forest

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Trophic Strategy

Food Habits

These animals are generally frugivorous, but fruits may be mixed with insects, leaves, and other vegetable matter. Usually ripe, pulpy fruit is preferred, so gibbons compete mainly with squirrels and birds, rather than other primates. Small vertebrates and eggs may be eaten occasionally. Generally, about 35 percent of the daily activity is spent feeding, and of that, up to 65 percent of the time is spent foraging for fruit (Chivers, 1977).

Animal Foods: birds; mammals; eggs; insects

Plant Foods: leaves; fruit

Primary Diet: herbivore (Frugivore )

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Associations

Ecosystem Roles

As frugivores, it is likely that these gibbons help in seed dispersal.

Ecosystem Impact: disperses seeds

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Predation

Details on predation of these gibbons in the wild are lacking. Because they are highly arboreal, and often occupy higher areas of the canopy, it is likely that most terrestrial predators never come in contact with them. Therefore, snakes and avian predators are likely to be their biggest threats.

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Life History and Behavior

Behavior

Communication and Perception

As mentioned above, Hoolocks gibbons use duet calls to mark their territory. In addition to these vocal communications, they use body postures and facial expressions in communication. Tactile communication, including play and grooming, is probably important within the family unit.

Communication Channels: visual ; tactile ; acoustic

Other Communication Modes: duets

Perception Channels: visual ; acoustic

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Life Expectancy

Lifespan/Longevity

Gibbons can live as long as 44 years in captivity. although in the wild, they are more likely to live 20 to 25 years.

Range lifespan

Status: captivity:
44 (high) years.

Typical lifespan

Status: wild:
20 to 25 hours.

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Lifespan, longevity, and ageing

Maximum longevity: 41 years (captivity) Observations: One animal caught as an adult was over 41 years of age when it died in captivity. Severe tooth erosion was reported (Richard Weigl 2005).
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Reproduction

Like all gibbon species, B. hoolock is monogamous (Nowak, 1999).

Mating System: monogamous

Normally a single young is born, sometimes twins, every 2 to 3 years. Gestation in gibbons is typically around 7 months. Births typically from November to March. The estrous cycle averages 28 days. Young are weaned after 1.5 to 2 years, and they usually reach sexual maturity in 8 to 9 years, although gibbons in captivity are known to have reached maturity 2 to 3 years earlier. In the wild, gibbons typically leave their parents at the time they reach sexual maturity to form breeding pairs of their own. The typical life span in the wild may exceed 20 to 25 years, but several closely related species in captivity have lived for up to 45 years (Chivers, 1977).

Breeding interval: These gibbons breed every 2 to 3 years.

Breeding season: These animals breed so that births are timed to occur between November and March.

Range number of offspring: 1 to 2.

Average gestation period: 7 months.

Range weaning age: 18 to 24 months.

Range time to independence: 8 to 9 years.

Range age at sexual or reproductive maturity (female): 8 to 9 years.

Range age at sexual or reproductive maturity (male): 8 to 9 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous

After the young is born, it clings tightly to the mother around the waist and remains there for the first few months of its life. Weaning occurs gradually, in 1.5 to 2 years. Young gibbons typically remain with their parents until they reach sexual maturity. During this extensive association, they may help with the rearing of their siblings. Males also help to raise the young.

Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Provisioning: Female, Protecting: Male, Female); post-independence association with parents; extended period of juvenile learning

  • Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.
  • Chivers, D. 1977. The lesser apes. Pp. 539-598 in Prince Rainier, G Bourne, eds. Primate Conservation. New York: Academic Press.
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
A2acd+3cd+4acd

Version
3.1

Year Assessed
2008

Assessor/s
Brockelman, W., Molur, S. & Geissmann, T.

Reviewer/s
Mittermeier, R.A. & Rylands, A.B. (Primate Red List Authority)

Contributor/s

Justification
Listed as Endangered as there is reason to believe the species has declined by at least 50% over the past 40 years (approximately three generations) due primarily to hunting and habitat loss. Over the coming 40 years, this decline is likely to reach similar proportions due to continuing habitat loss.

History
  • 2000
    Endangered
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Currently, much of the habitat appropriate for Hoolock gibbons is being destroyed for lumber, firewood, and farming (Nowak, 1999). These animals are also a highly desired food source in parts of India and as such, are found in decreasing numbers. In recent years, several sanctuaries and reserves that lie inside the natural range of Hoolock gibbons have been created. However, the increased problem of habitat fragmentation is still of much concern (Wolfheim, 1983).

US Federal List: endangered

CITES: appendix i

IUCN Red List of Threatened Species: no special status

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Population

Population
There are estimated to be about 200-280 hoolocks in Bangladesh (Islam et al. 2006; Molur et al. 2005). In China, a population has been identified in Medog Nature Reserve in southeastern Tibet, just across the border from Arunachal Pradesh, but the identity of this taxon is not established and there has been no survey conducted to determine the population numbers (W. Bleisch pers. comm.).

This species occurs in several of India’s northeastern states, but populations there tend to be isolated. It is common in certain areas of occurrence, but rare in others due to intense hunting by local tribes (Choudhury 1991), and is considered rare throughout its range (Choudhury 2001). The species was found in all forested patches in northeastern India about 30 years ago, but they are reduced to a few forest fragments now. The total population in northeastern India was estimated to be about 2,600, of which the majority—about 2,000—occurs in the state of Assam (Molur et al. 2005). A population of about 170 gibbons has more recently been identified as H. leuconedys (Das et al. 2006) and should be subtracted from the population estimate if this identity is proven. Moreover, there are surveys needed in Mehao region, where there is uncertainty as to which species the gibbons there represent (Das et al. 2006; Das pers. comm.). Namdapha National Park in the Changlang District of Arunachal Pradesh is a relative stronghold for this species in India, offering the population there its largest contiguous stretch of protected habitat (Chetry et al. 2003).

There are no population estimates available for Myanmar. It is possible that the largest and most viable populations of western hoolock are to be found in this country, where at present almost no attention is paid to it (W. Brockelman pers. comm.). There are several thousand square kilometers of unsurveyed forest habitat in the central-west and north-west of this country, with a particular need to survey the western areas west of Chindwin/Ayerawady River. There are reports of gibbons in Rakhine Yoma Elephant Range, but there is no knowledge of the actual population level there (W. Brockelman pers. comm. 2006). The western part of Hukuang Tiger Reserve with a large area of forest (>1,000 km2) has not been surveyed, but is likely to have this species. The northern limit is just south of Hkakaraborazi National Park.

Population Trend
Decreasing
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Threats

Major Threats
In Bangladesh, the main threats are the combined effects of habitat loss, fragmentation, human interference and hunting (Islam and Feeroz 1992; Molur et al. 2005). Hunting is universal all over Bangladesh as well as India, and may be in Myanmar also. In China, the Tibetan population could be under threat from hunting for food or non-targeted hunting, but this is not established.

In some Indian locales, these animals are rare due to large scale hunting for food and because some ethnic groups believe the gibbons have medicinal properties (Gupta 2005; J. Das pers. comm.). Additionally, jhoom cultivation threatens the habitats of Indian populations, some of which are relatively isolated already (Choudhury 1991). Affecting all northeastern Indian primate populations are harvesting of bamboo for paper mills, oil mining and exploration, and coal mining, which deplete habitat and cause pollution and disturbance (Choudhury 2001). Habitat fragmentation and loss are major threats in India (Molur et al. 2005). Small and restricted groups may not be viable because of genetic and demographic instabilities and because they are more affected by hunting pressure and habitat loss. Many small forest fragments are reported to have only one or a few gibbon groups. These have limited chances of surviving more than a few generations without translocation.

In Myanmar, shifting cultivation is a major threat, and so is hunting. Although logging is restricted on the western side of the Chindwin, it is still considered a threat for this species. Political and ethnic conflicts have prevented the Myanmar government to promote development and conservation activities effectively in areas of northwestern and central western Myanmar along the borders with India and Bangladesh. Thus, most conservation efforts have been concentrated within the range of H. leuconedys.
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Management

Conservation Actions

Conservation Actions
This species is listed on CITES Appendix I and on schedule I of the Indian Wildlife (Protection) Act of 1972. Overall, it is found in 30 protected areas in India (Choudhury 2001) and many others throughout its range.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Hoolock gibbons occupy prime tea growing regions in southeast Asia (Chivers, 1977). Any preservation of their habitat may impact tea industries.

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Economic Importance for Humans: Positive

Although less common than siamangs, Hoolock gibbons are sometimes found in zoos. Additionally, their meat is highly prized in parts of eastern India (Chivers, 1977).

Positive Impacts: food ; research and education

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Wikipedia

Western hoolock gibbon

The western hoolock gibbon (Hoolock hoolock) is a primate from the gibbon family, Hylobatidae. The species is found in Assam, Bangladesh and in Myanmar west of the Chindwin River.[2]

Classification[edit]

Mootnick and Groves[3] 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 which were later have found that the 2 species have a bigger difference to that of white handed gibbons than bonobos to chimpanzees.[4]

Habitat[edit]

In India and Bangladesh it is found where there is contiguous canopy, broad-leaved, wet evergreen and semi-evergreen forests dipterocarpus forest often mountainous. The species is an important seed disperser; its diet includes mostly ripe fruits, with some flowers, leaves and shoots.[citation needed]

Conservation[edit]

There are numerous threats to western hoolock gibbons in the wild, and are now entirely dependent on human action for their survival. Threats include habitat encroachment by humans, forest clearance for tea cultivation, the practice of jhuming (slash-and-burn cultivation), hunting for food and “medicine”, capture for trade, and forest degradation.[1]

Over the last 30–40 years, western hoolock gibbon numbers are estimated to have dropped from more than 100,000 (Assam alone was estimated to have around 80,000 in the early 1970s) to less than 5,000 individuals (a decline of more than 90%).[5] In 2009 it was considered to be one of the 25 most endangered primates,[6] though it has been dropped from the later editions of the list. [7]

Diet[edit]

Hoolock gibbons feed submissively on leaves and flower buds from the forest canopy, but fresh fruits are mainly part of their diet as well.[citation needed]

See also[edit]

References[edit]

  1. ^ a b Brockelman, W., Molur, S. & Geissmann, T. (2008). Hoolock hoolock. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 4 January 2009.
  2. ^ 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. 
  3. ^ 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. 
  4. ^ Mootnick, A. R. (2006). "Gibbon (Hylobatidae) species identification recommended for rescue or breeding centers". Primate Conserv 21: 103–138. doi:10.1896/0898-6207.21.1.103. 
  5. ^ "Western Hoolock Gibbon, Hoolock hoolock". Retrieved 2008-03-10. 
  6. ^ Mittermeier, R.A.; Wallis, J.; Rylands, A.B.; Ganzhorn, J.U.; Oates, J.F.; Williamson, E.A.; Palacios, E.; Heymann, E.W.; Kierulff, M.C.M.; Long, Yongcheng; Supriatna, J.; Roos, C.; Walker, S.; Cortés-Ortiz, L.; Schwitzer, C., eds. (2009). Primates in Peril: The World's 25 Most Endangered Primates 2008–2010. Illustrated by S.D. Nash. Arlington, VA: IUCN/SSC Primate Specialist Group (PSG), International Primatological Society (IPS), and Conservation International (CI). pp. 1–92. ISBN 978-1-934151-34-1. 
  7. ^ Mittermeier, R.A.; Schwitzer, C.; Rylands, A.B.; Taylor, L.A.; Chiozza, F.; Williamson, E.A.; Wallis, J., eds. (2012). Primates in Peril: The World's 25 Most Endangered Primates 2012–2014. Illustrated by S.D. Nash. IUCN/SSC Primate Specialist Group (PSG), International Primatological Society (IPS), Conservation International (CI), and Bristol Conservation and Science Foundation. pp. 1–40. 
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