Learn About The Western Hoolock Gibbons
The Western Hoolock Gibbon (Hoolock Hoolock) is a primate from the gibbon family, Hylobatidae. The species is found in Assam, Mizoram, and Meghalaya in India, Bangladesh, and Myanmar west of the Chindwin River.
Hoolocks are the second-largest of the gibbons, after the Siamang. They reach a size of 60 to 90 cm and weigh 6 to 9 kg. The sexes are about the same size, but they differ considerably in coloration; males are black-coloured with remarkable white brows, while females have a grey-brown fur, which is darker at the chest and neck. White rings around their eyes and mouths give their faces a mask-like appearance. The Oxford English Dictionary says that the name "hoolock" is from "a language of Assam."
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Distribution
In northeast India, the hoolock is found south of Brahmaputra and the North Bank areas and east of the Dibang Rivers. Its range extends into seven states covering Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura (The seven northeastern states of India). The species are protected in India in the Hollongapar Gibbon sanctuary, which support 125 Individuals of the species, as of 2023. In Bangladesh, the western hoolock gibbons were distributed across 35 forest fragments. The largest of these (Lawachara and Kaptai) supported 42 and 84 individuals respectively, but 17 of the fragments had less than ten individuals. For a better overview the forest fragments are grouped into 13 areas. All areas are located within Chittagong and Sylhet divisions, mostly near the eastern border of the country. In China, in historical times, the Skywalker Gibbon was recorded in nine counties in the west bank of the Salween River in westernmost Yunnan province. Based on more recent interview surveys conducted in October–November 2008 and field surveys conducted in Mar, Apr, and Aug 2009, the current Chinese population of hoolock gibbons was found to be restricted to three counties (Baoshan, Tengchong, and Yingjiang). The population size was estimated to be less than 200 individuals. In Myanmar, all three species of hoolock gibbon can be found in the forested areas west of Thanlwin river. Of all four distribution countries, Myanmar holds the key population of all three species.
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Classification
The classification of this gibbon has changed several times in the past few years. Classically, all gibbons were classified in the genus Hylobates, with the exception of the Siamang. After some studies, the genus was divided into three sub-genera (including the Siamangs Symphalangus), and then into four (recognizing Bunopithecus as the Hoolock sub-genus distinct from other gibbon subgenera). These four subgenera were elevated to full genus status. However, the type species for Bunopithecus is Bunopithecus Sericus, an extinct gibbon or gibbon-like ape from Sichuan, China. Very recent investigations have shown that the hoolock gibbons are not closely related to B. Sericus, so they have been placed in their own genus, Hoolock. In the process, the two subspecies of hoolock gibbons have been raised to species level. A new subspecies of the western hoolock gibbon has been described recently from northeastern India, which has been named the Mishmi Hills hoolock gibbon, H. Hoolock Mishmiensis. A further new species, H. Tianxing, with an estimated population of about 200, was discovered in southwest China in 2017.
Distribution
In northeast India, the hoolock is found south of Brahmaputra and the North Bank areas and east of the Dibang Rivers. Its range extends into seven states covering Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura (The seven northeastern states of India). The species are protected in India in the Hollongapar Gibbon sanctuary, which support 125 Individuals of the species, as of 2023. In Bangladesh, the western hoolock gibbons were distributed across 35 forest fragments. The largest of these (Lawachara and Kaptai) supported 42 and 84 individuals respectively, but 17 of the fragments had less than ten individuals. For a better overview the forest fragments are grouped into 13 areas. All areas are located within Chittagong and Sylhet divisions, mostly near the eastern border of the country. In China, in historical times, the Skywalker Gibbon was recorded in nine counties in the west bank of the Salween River in westernmost Yunnan province. Based on more recent interview surveys conducted in October–November 2008 and field surveys conducted in Mar, Apr, and Aug 2009, the current Chinese population of hoolock gibbons was found to be restricted to three counties (Baoshan, Tengchong, and Yingjiang). The population size was estimated to be less than 200 individuals. In Myanmar, all three species of hoolock gibbon can be found in the forested areas west of Thanlwin river. Of all four distribution countries, Myanmar holds the key population of all three species.
Vocalisation
Like other gibbons, hoolock gibbon pairs produce a loud, elaborate song, usually as a duet from the forest canopy, in which younger individuals of the family group may join. The song includes an introductory sequence, an organising sequence, and a great call sequence, with the male also contributing to the latter (unlike in some other gibbon species).
Habitat and Diet
In India and Bangladesh, the Western Hoolock Gibbon is found where the canopy is contiguous, broad-leaved, wet evergreen and mixed evergreen forests, including dipterocarp forests and often in mountainous terrain. The species is an important seed disperser; its diet includes mostly ripe fruits, with some flowers, leaves, and shoots. The Western Hoolock Gibbon also feeds on non-plant items such as silkworms, ants, and various other insect species. During the monsoon season of Northeast India, insects are recorded to be this species' second preferred food item, behind Artocarpus Chaplasha, a fruit bearing tree in the same genus of Jack-Fruit.
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Taxonomy
Kingdom
Phylum
Class
Family
Order
Animalia
Chordata
Mammalia
Primates
Hylobatidae
CLASSIFICATION
The classification of this gibbon has changed several times in the past few years. Classically, all gibbons were classified in the genus Hylobates, with the exception of the Siamang. After some studies, the genus was divided into three sub-genera (including the Siamangs Symphalangus), and then into four (recognizing Bunopithecus as the Hoolock sub-genus distinct from other gibbon subgenera). These four subgenera were elevated to full genus status. However, the type species for Bunopithecus is Bunopithecus Sericus, an extinct gibbon or gibbon-like ape from Sichuan, China. Very recent investigations have shown that the hoolock gibbons are not closely related to B. Sericus, so they have been placed in their own genus, Hoolock. In the process, the two subspecies of hoolock gibbons have been raised to species level. A new subspecies of the western hoolock gibbon has been described recently from northeastern India, which has been named the Mishmi Hills hoolock gibbon, H. Hoolock Mishmiensis. A further new species, H. Tianxing, with an estimated population of about 200, was discovered in southwest China in 2017.
RANGE DESCRIPTION
This species is found in eastern Bangladesh, northeastern India (Assam, Arunachal Pradesh, 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 (northeastern most India) before that habitat was cultivated for agriculture and tea are not so any more (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 Hoolock leuconedys in Arunachal Pradesh, northeast India, which has traditionally been considered to be part of the range of H. hoolock.
CLASSIFICATION
The classification of this gibbon has changed several times in the past few years. Classically, all gibbons were classified in the genus Hylobates, with the exception of the Siamang. After some studies, the genus was divided into three sub-genera (including the Siamangs Symphalangus), and then into four (recognizing Bunopithecus as the Hoolock sub-genus distinct from other gibbon subgenera). These four subgenera were elevated to full genus status. However, the type species for Bunopithecus is Bunopithecus Sericus, an extinct gibbon or gibbon-like ape from Sichuan, China. Very recent investigations have shown that the hoolock gibbons are not closely related to B. Sericus, so they have been placed in their own genus, Hoolock. In the process, the two subspecies of hoolock gibbons have been raised to species level. A new subspecies of the western hoolock gibbon has been described recently from northeastern India, which has been named the Mishmi Hills hoolock gibbon, H. Hoolock Mishmiensis. A further new species, H. Tianxing, with an estimated population of about 200, was discovered in southwest China in 2017.
VOCALISATION
Like other gibbons, hoolock gibbon pairs produce a loud, elaborate song, usually as a duet from the forest canopy, in which younger individuals of the family group may join. The song includes an introductory sequence, an organising sequence, and a great call sequence, with the male also contributing to the latter (unlike in some other gibbon species).
HABIT AND DIET
In India and Bangladesh, the Western Hoolock Gibbon is found where the canopy is contiguous, broad-leaved, wet evergreen and mixed evergreen forests, including dipterocarp forests and often in mountainous terrain. The species is an important seed disperser; its diet includes mostly ripe fruits, with some flowers, leaves, and shoots. The Western Hoolock Gibbon also feeds on non-plant items such as silkworms, ants, and various other insect species. During the monsoon season of Northeast India, insects are recorded to be this species' second preferred food item, behind Artocarpus Chaplasha, a fruit bearing tree in the same genus of Jack-Fruit.
BREEDING AND LIFECYCLE
Young hoolocks are born after a 7-month gestation, with milky white or buff-coloured hair. After one year, the hair of both sex darken and turn black. At puberty the females' hair turn buff-colour and the male turn Pitch black. After 8–9 years, they are fully mature and their fur reaches its final coloration. Their life expectancy in the wild is on average 25 years but can be longer.
DAILY LIFE AND GROUP DYNAMICS
Hoolock gibbons live in small monogamous family groups of up to six individuals. They descend in the early morning hours from their sleeping sites, which are usually located in the tallest trees at high elevations, to the valley below where they like to forage. They forage in trees, hanging by one arm or sitting on a branch.
After feeding, they perform their songs for up to 20 minutes.
The gibbons travel an average of half a mile (about 1 km) per day, swinging from branch to branch very swiftly at speeds that can reach 12 mph (20 km/h), and earning them the nickname “acrobats of the canopy.” Although strictly arboreal, swinging is not their only mode of locomotion. They can walk upright on two legs with arms extended out like tightrope walkers. In fact, the only primates that walk on two legs more regularly than gibbons are humans.