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Bunopithecus hoolockhoolock gibbon

By Matthew Krebs

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). (Wolfheim, 1983)

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). (Wolfheim, 1983)

  • Range elevation
    152 to 1,370 m
    498.69 to ft

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). (Chivers and Gitins, 1978; Nowak, 1999)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    6 to 7 kg
    13.22 to 15.42 lb

Reproduction

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

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). (Chivers, 1977; Nowak, 1999)

  • 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

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. (Chivers, 1977; Nowak, 1999)

  • 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

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. (Chivers, 1977; Nowak, 1999)

  • Range lifespan
    Status: captivity
    44 (high) years
  • Typical lifespan
    Status: wild
    20 to 25 hours

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).

Home Range

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

  • Other Communication Modes
  • duets

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). (Chivers, 1977)

  • 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). (Chivers, 1977)

  • Positive Impacts
  • 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. (Chivers, 1977)

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). (Nowak, 1999; 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.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

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

Glossary

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

diurnal
  1. active during the day, 2. lasting for one day.
duets

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

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

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

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.

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