Bunopithecus hoolock
hoolock gibbon

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)

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)

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)

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)

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)

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.

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)

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.

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

Hoolock gibbons occupy prime tea growing regions in southeast Asia (Chivers, 1977). Any preservation of their habitat may impact tea industries. (Chivers, 1977)

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)

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)

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.