Bunopithecus hoolock

Geographic Range

Hylobates 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 oriental
  • native native

Habitat

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).

• Habitat Regions
• tropical tropical
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• rainforest rainforest
• scrub forest scrub forest

Physical Description

Hylobates 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, H. hoolock has only 38 chromosomes, compared to 44 in other members of its subgenus (Nowak, 1999).

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes colored or patterned differently
• male more colorful

Reproduction

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

• Mating System
• monogamous 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).

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

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.

Behavior

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 (Nowak, 1999).

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 (Chivers, 1977).

• Key Behaviors
• arboreal arboreal
• diurnal diurnal
• motile motile
• sedentary sedentary
• territorial territorial
• social social

Home Range

In Assam and Bangladesh, the average territory size is 22 ha (Nowak, 1999)

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 visual
• tactile tactile
• acoustic acoustic

• Other Communication Modes
• duets duets

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

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).

• Primary Diet
• herbivore herbivore
  • frugivore frugivore

• Animal Foods
• birds
• mammals
• eggs
• insects

• Plant Foods
• leaves
• fruit

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.

Ecosystem Roles

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

• Ecosystem Impact
• disperses seeds

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 food
• research and education

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.

Conservation Status

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).

Other Comments

Hoolock gibbons are known to swim well, but rarely do so and will go out of their way to avoid water (Roonwal and Mohnot, 1977). Hoolock gibbons were previously recognized under the name Hylobates hoolock .

Additional Links

Encyclopedia of Life

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Matthew Krebs (author), University of California, Berkeley, James Patton (editor), University of California, Berkeley.

References

Chivers, D., S. Gitins. 1978. Diagnostic features of gibbon species. International Zoo Yearbook , 18: 157-173.

Chivers, D. 1977. The lesser apes. Pp. 539-598 in Primate Conservation . New York: Academic Press.

Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition . Baltimore and London: The Johns Hopkins University Press.

Roonwal, M., S. Mohnot. 1986. Primates of South Asia . Cambridge, MA: Harvard University Press.

Wilson, D., D. Reeder. 1993. Mammal Species of the World . Washington: Smithsonian Institution Press.

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