HOOLOCK GIBBONS
Hoolock gibbons — formerly known by the scientific name Bunopithecus hoolock and now regarded as a genus with three species — are found in forested areas from eastern India and Bangladesh to Myanmar and southern China. Geographically, their natural extends east to the Salween River and west to the Brahmaputra River. Of all gibbon species, their range extends the farthest north and east. These apes live in thick evergreen, mixed evergreen, and scrub forests but prefer undisturbed forested areas and live at elevations from 152 to 1,370 meters (500 to 4,500 feet). [Source: Matthew Krebs, Animal Diversity Web (ADW) /=]
Gibbons are tree-swinging, small-bodied lesser apes not monkeys. They are the smallest of all apes; are found exclusively in Asia, mostly in India, Southeast Asia, Indonesia and to a lesser extent China; and live primarily in monsoon rain forests, mostly lowland forests. What distinguishes an ape from a monkey is the fact that the former doesn't have a tail. Gibbons are sometimes called “lesser apes" to distinguish them from the "greater apes" —humans, gorillas, chimpanzees and orangutans
Hoolock gibbons are said to be good swimmers but rarely do so and go out of their way to avoid water. They were previously recognized under the name Hylobates hoolock. Gibbons can live up to 44 years in captivity but in the wild, they tend to live 20 to 25 years.The Oxford English Dictionary says that the name "hoolock" is from "a language of Assam.".
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Hoolock Gibbon Species in the Hoolock Genus
The hoolock genus contains three species all with Hoolock in their name. Native to eastern Bangladesh, Northeast India, Myanmar, and Southwest China, they are the second-largest of the gibbons, after the siamang. They reach a size of 60 to 90 centimeters and weigh six to nine kilograms.
Western hoolock gibbons (Hoolock hoolock, Harlan, 1834) live in India, Bangladesh, and Myanmar. They are endangered. Eastern hoolock gibbons (Hoolock leuconedys, Groves, 1967) live in China (Yunnan Province). They are vulnerable. Skywalker hoolock gibbons (Hoolock tianxing, Fan et al., 2017) live in Myanmar and southwestern China. They are endangered. There are only 150 of them.
The Western hoolock gibbons is also known as the white-browed gibbons. It is India's and Bangladesh’s only ape. Males are black with white eye brows and have longer hair than other species. Loud howls follow tree-top trills. There are about 100,000 of them.
Hoolock Gibbon Characteristics and Food
Hoolock gibbons are the second largest gibbons after siamangs. They Hoolock gibbons have a head and body length of 45 to 58 centimeters (19 to 23 inches) and range in weight from six to eight kilograms (13.2 to 17.6 pounds). Sexual Dimorphism (differences between males and females) is present: Sexes are colored or patterned differently with the male being more colorful. [Source: Matthew Krebs, Animal Diversity Web (ADW) /=]
Hoolock gibbons have longer hair than other gibbons and are characterized curved white brow streaks, and faintly triangular-shaped head. White rings around their eyes and mouths give their faces a mask-like appearance. According to Animal Diversity Web: 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 fur on their hands and feet. Unique among gibbon species, B. hoolock has only 38 chromosomes, compared to 44 in other members of its subgenus.
Hoolock gibbons are primarily frugivore (fruit eating) but are also considered herbivores (primarily eat plants or plants parts). Among the plant foods they eat are leaves and vegetable matter. Animal foods include birds, mammals, eggs, insects. Gibbons prefer ripe, pulpy fruit and compete with birds and small mammals for these foods. Typically about 35 percent of daily activity is spent feeding, and of that, up to 65 percent of that time is spent foraging for fruit.
Hoolock Gibbon Behavior and Communication
Hoolock gibbons are arboreal (live mainly in trees), diurnal (active during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), territorial (defend an area within the home range) andsocial (associates with others of its species; forms social groups). In Assam and Bangladesh, the average home range size is 22 hectares [Source: Matthew Krebs, Animal Diversity Web (ADW) /=]
The mated pair, along with their offspring (typically one or two), occupy a fiercely defended and stable territory. Occasionally, lone adults — usually sub-adults recently forced from their family group — will establish solitary territories. /=\
Hoolock gibbons communicate with vision, touch and sound and using vision, touch, sound and chemicals usually detected with smell. They also employ duets (joint displays, usually between mates, and usually with highly-coordinated sounds) to communicate and mark their territory. In addition to this, according to Animal Diversity Web, they use body postures and facial expressions in communication. Tactile communication, including play and grooming, is probably important within the family unit. /=\
The loud calls of the gibbon are used to identify individuals within and outside the family group. Calls are probably used mainly for territorial, defense, and the male and female will intimidate neighbors and mark their territory by singing a duet. Unlike other gibbon species, in Hoolock gibbons, male and female vocalizations are the same, and comparitvely quite simple. These calls consist of a rapid, accelerating and alternating series of low and high notes. /=\
Hoolock Gibbon Mating, Reproduction and Offspring
Like all gibbon species, hoolock gibbons are monogamous (have one mate at a time). They engage in seasonal breeding, typically breeding every two to three years, with births timed to occur between November and March. The estrous cycle averages 28 days. The number of offspring ranges from one to two. Normally a single young is born, sometimes twins, every two to three years. [Source: Matthew Krebs, Animal Diversity Web (ADW) /=]
The average gestation period is seven months. 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 Young are weaned gradually after 1.5 to two years. During the pre-weaning stage and pre-independence stages provisioning provisioning is done by females and protecting is done by males and females. The post-independence period is characterized by the association of offspring with their parents. /=\
There is an extended period of juvenile learning. 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. Hoolock gibbons usually reach sexual maturity in eight to nine years, although gibbons in captivity are known to have reached maturity two to three years earlier. In the wild, gibbons typically leave their parents at the time they reach sexual maturity to form breeding pairs of their own.
Hoolock Gibbons, Humans and Conservation
There seems to be a fair number of Western Hoolock gibbons in fragmented ranges in India and Bangladesh. Eastern Hoolock gibbons and Skywalker Hoolock gibbons are more scare. There are only 150 Skywalker Hoolock gibbons.
On the International Union for Conservation of Nature (IUCN) Red List Hoolock gibbons are listed as No special status. On the US Federal List they are classified as Endangered. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix I, which lists species that are the most endangered among CITES-listed animals and plants. [Source: Matthew Krebs, Animal Diversity Web (ADW) /=]
Humans utilize Hoolock gibbons for food, research and education. Although less common than siamangs, Hoolock gibbons are sometimes found in zoos. Their meat is valued in parts of eastern India. Hoolock gibbons occupy prime tea growing regions in southeast Asia. Preservation of their habitat may impact tea industries. /=\
Currently, much of the habitat possibly used by Hoolock gibbons is being degraded or destroyed for lumber, firewood, local farming and plantation agriculture for tea, palm oil, rubber and other crops. In recent years, several sanctuaries and reserves have been set up that occur in natural range of Hoolock gibbons. However, habitat fragmentation remains a serious problem.
Image Sources: Wikimedia Commons
Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.
Last updated December 2024