Western Hoolock Gibbon

The western hoolock gibbon is India's only ape. It is a canopy-dwelling ape of evergreen hill forest. Adults differ in colour: males are black and slightly larger, while females have light brown to golden fur (Gogoi and Sharma, Down To Earth 2025). Pairs are best known by their song, a loud, elaborate duet sung from the treetops, in which the young of the family may join. The song builds through an introduction to a great-call sequence that the male also takes part in (Wikipedia, general species account).

Hoolocks live in small family groups of two to five, usually a pair that stays together for life plus their young (Gogoi and Sharma, Down To Earth 2025). They are found only where the forest canopy is continuous. They eat mainly ripe fruit, which makes them important seed dispersers, and add flowers, leaves, shoots and insects. In northeast India, insects become their second most important food during the monsoon, behind the fruit of a jackfruit relative, Artocarpus chaplasha (Wikipedia, general species account).

Hoolock numbers have fallen by more than 90% since the 1980s: Assam alone was thought to hold around 80,000 in the early 1970s, and the species as a whole may now number fewer than 5,000 (Wikipedia, general species account). Tree felling breaks up the canopy they depend on. The best-known site is the Hollongapar Gibbon Sanctuary near Jorhat in Assam, less than 21 km² of forest ringed by tea gardens and split in two by a railway line (Gogoi and Sharma, Down To Earth 2025).