1. Profile (Picture)
2. Tidbits
3. Status and Trends (IUCN Status, Countries Where Currently Found, Population
Estimates, History of
Distribution, Threats/Reasons for Decline)
4. Data on Biology and Ecology (Size
and Weight, Habitat, Age to Maturity, Gestation Period, Birth
Season, Birth Rate, Early Development, Diet, Behavior, Social Organization, Age and Gender Distribution, Density)
5. References
Pictures: Adult Female Hoolock Gibbon (30 Kb JPEG) (Gibbon Res. Lab); Eastern Hoolock Gibbon (36 Kb JPEG) (Intl. Gibbon Ctr.); Hoolock Gibbon (11 Kb JPEG) (Sci. Mus. China)
The hoolock gibbon is a small arboreal ape weighing a little over 6 kg (13 lb). It exhibits sexual dichromatism: the adult male is always black, except for its prominent white eyebrows, while the adult female is gold or buff or brownish buff. The hoolock gibbon is found in good quality semi-deciduous/evergreen forest up to 1400 m (4500'). Fruit comprises the majority of its diet, which also includes leaves, flowers, buds and a small amount of insects and spiders.
The hoolock gibbon is arboreal and diurnal. During the hot hours of the day it retires to the
lower, more shady trees and rests. Hoolock gibbons live in small, monogamous
family groups, consisting of a mated pair with their offspring. The size of a
group ranges from 2 - 6 members. There are deep social bonds between group
members. Mother-infant
interactions are common. A hoolock gibbon family group maintains a definite territory, which is defended by loud
and frequent territorial songs.
The hoolock gibbon was formerly widespread from eastern India, through Bangladesh
to China and south to the Irrawaddy River in Myanmar. Because of threats such as habitat loss and
hunting, its numbers have decreased, although there are no firm population
estimates. Currently it is thought to occur south
and east of the Brahmaputra River in Assam (India) and Bangladesh, as well as in southern
Yunnan (China) and Myanmar
*** The hoolock gibbon was first listed by scientists as a separate species in 1879, when it was recorded from western Yunnan (China) and from Mt. Kachin, Myanmar (Ma et al. 1988).
*** "Hylobates" (the former genus name for gibbons) means "dweller in the trees," and gibbons fully justify the name. They exceed all other animals in agility at traveling through the trees. (Nowak 1999)
*** When their habitat is fragmented, gibbons are forced to descend from trees to cross clearings. This makes them vulnerable to hunting and predation.
2004: Occurs in Bangladesh, China (Yunnan), India (Assam) and Myanmar. (IUCN 2004)
[Note: Figures given are for wild populations only.]
The hoolock gibbon was formerly widespread from eastern India, through Bangladesh to China and south to the Irrawaddy River in Myanmar. In 1967 it was reported to occur in Assam (India), upper Myanmar and Tenasserim (Myanmar), northern Thailand and northern Laos. By 1987 it had declined drastically, particularly in Bangladesh and India, and was thought to be located in India, the east of Bangladesh, Myanmar, and Yunnan Province in China. Although there are no firm populations estimates available, currently it is thought to occur south and east of the Brahmaputra River in Assam (India) and Bangladesh, as well as in south Yunnan (China) and Myanmar (Sati & Alfred 2001, IUCN 2004).
Distribution Map (6 Kb GIF) (Sati & Alfred 2001)
The hoolock gibbon has declined mainly due to habitat loss. It is currently threatened by continued habitat loss and fragmentation through shifting cultivation and logging. In addition, severe hunting pressure by local tribesmen is reported in Assam. Gibbon meat and bones are valued for use in Oriental medicine.
The head and body length of an adult hoolock gibbon usually measures 46 - 63 cm (18 - 25"). A female weighs 6.0 - 6.6 kg (13.2 - 14.5 lb) and a male weighs 6.1 - 7.9 kg (13.4 - 17.4 lb). (Sati & Alfred 2001)
The hoolock gibbon is found in tropical evergreen rainforest, semi-evergreen forest, tropical mixed deciduous-dominated forest, and sub-tropical broadleaf hill forest up to 1400 m (4500'). (WCMC/WWF 1997) It prefers the closed canopy/three- tiered forest (high, middle and low) vegetation. Trees in the high tier support sleeping, resting and sun basking, while the trees in the middle and low tiers provide locomotion paths and food. (Sati & Alfred 2001)
The hoolock gibbon is one of the species that live in both the Himalaya, Indo-Burma and Mountains of Southwest China Biodiversity Hotspots (Cons. Intl. 2005) and the Northern Indochina Subtropical Moist Forests and Kayah-Karan/Tenasserim Moist Forests Global 200 Ecoregions. (Olson & Dinerstein 1998, Olson & Dinerstein 1999)
Sexual maturity in both sexes is attained at approximately 7 years (Sati & Alfred 2001).
195 - 210 days (Sati & Alfred 2001).
Generally the infant is born during winter (November - March) (Sati & Alfred 2001). Mating time is early in the rainy season (Roonwal & Mohnot 1977).
A single young is usually born. The time between births is usually 2 - 3 years.
The mother-infant bond in hoolock gibbons is very strong, with the mother protecting the infant from other group members as well as sympatric species. The newly born infant always clings to the mother’s belly and feeds on her milk for up to 6 months, after which weaning starts. The mature newborn, which spends time feeding and playing with other group members, always shares the night bed with its mother until another baby is born. (Sati & Alfred 2001)
Like most of the gibbon species, the hoolock gibbon is frugivorous. Fruit (mainly figs) comprises the majority of its diet, which also includes leaves, flowers, buds and a small amount of insects and spiders. (Sati & Alfred 2001)
The hoolock gibbon is almost entirely arboreal. It sleeps in a sitting posture, with its head buried between its knees. When alarmed, it hides in the foliage. It sometimes enters villages to plunder cultivated gardens. It has an aversion to large bodies of water such as rivers, al though it can swim well. The hoolock gibbon is diurnal. During the hot hours of the day it retires to the lower, more shady trees, where it rests in silence. (Roonwal & Mohnot 1977)
The hoolock gibbon moves either by brachiation, by leaping or jumping between the trees when the distance is not within reach by brachiation, by bipedally walking on tree trunks or on the ground, or by acrobatic and climbing movements on vines and tree trunks. Its light body and long and strong arms help it to exploit the terminal branches of trees and vines via brachiation. (Sati & Alfred 2001) When walking on the ground, it usually holds its long arms upward or horizontal, evidently for balance (Roonwal & Mohnot 1977).
Each group is said to hunt within its own territory, where it follows the same trail through treetops day after day. These paths can be traced by the worn-out condition of the branches. (Roonwal & Mohnot 1977)
Hoolock gibbons live in small, monogamous family groups, consisting of a mated pair with their offspring. The size of a group ranges from 2 - 6 members. The mean group size was 3 - 3.4 members for 5 studies in Bangladesh and India. There are deep social bonds between group members. The group members indulge in social activities such as grooming, playing, and sun basking. Mother-infant interactions are common. (Sati & Alfred 2001)
A hoolock gibbon family group maintains a definite territory, which is defended by loud and frequent territorial songs. The territory of a group, regardless of the group's size, usually ranges between 15 - 35 hectares (38 - 88 acres). Aggression and conflicts between groups usually take place in areas where the territories of two or more groups overlap. (Sati & Alfred 2001)
The male:female ratio is approximately 1:1 (Sati & Alfred 2001).
Some measurements of population and group densities include: 2.2 groups/sq km (5.7 groups/sq mi) (northeastern India), 4.4 individuals/sq km (11.4 individuals/sq mi) (Bangladesh), 1.5 groups/sq km (3.9 groups/sq mi) and 5.3 individuals/sq km (13.8 individuals/sq mi) (Sylhet, Bangladesh) (Sati & Alfred 2001).
Burton & Pearson 1987, Cons. Intl. 2005, Gibbon Res. Lab, Gittins & Akonda 1982, Haimoff et al. 1987, IUCN 1994, IUCN 1996, IUCN 2000, IUCN 2003a, IUCN 2004, Ma et al. 1988, Macdonald 1984, Nowak 1999, Nowak & Paradiso 1983, Olson & Dinerstein 1998, Olson & Dinerstein 1999, Roonwal & Mohnot 1977, Sati & Alfred 2001, Schuhmacher 1967, Sci. Mus. China, WCMC/WWF 1997, Zhang 1998
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