India's only ape species swings through fragmented forests that shrink yearly. Acoustic monitoring reveals territories compressed to lethal proximity. Two family groups cannot coexist where three lived decades ago.
The Singing Ape of Assam
In the hill forests of Karbi Anglong, Assam, hosts India's only ape, the western hoolock gibbon (Hoolock hoolock). This primate is known for its dramatic form of locomotion, called brachiation, where it swings arm-over-arm through the forest canopy at high speeds. A family group consists of a monogamous pair and their offspring, and they are intensely territorial. Their territories are defined not by physical markers, but by sound. Each morning, mated pairs perform a loud, elaborate duet, a haunting song that travels for kilometers through the forest to warn other gibbons away from their patch of fruit-bearing trees.
The species displays striking sexual dimorphism in its pelage. Males are entirely black except for a prominent white brow, while females are a creamy buff or grey-blond color with darker hair on their chest and neck. A juvenile of either sex is born with a light-colored coat, which turns black. A female's coat will lighten again as she reaches subadulthood. Primarily frugivorous, they feed on over 100 plant species, with a preference for ripe figs. This diet makes them important seed dispersers, a function that maintains the health and diversity of the forest ecosystem.
The International Union for Conservation of Nature (IUCN) classifies the western hoolock gibbon as Endangered. The population has experienced a catastrophic decline from an estimated 100,000 individuals a few decades ago to fewer than 5,000 today.
Forests Under Pressure
The primary driver of the gibbon's decline is severe habitat loss and fragmentation. The Karbi Anglong district, an important habitat for the species, lost over 25% of its dense forest cover in less than a decade. This destruction is caused by logging, agricultural expansion, and infrastructure projects like railway lines and oil exploration. A particularly damaging practice is jhum, or slash-and-burn cultivation. Historically, jhum cycles involved long fallow periods of 15-20 years, allowing forests to regenerate. Due to population pressure, these cycles have shrunk to as little as 2-3 years, preventing forest recovery and leading to permanent degradation.
This fragmentation has direct consequences for the gibbons. As an arboreal species that rarely descends to the ground, they require continuous forest canopy to travel, forage, and find mates. Gaps in the canopy, some as wide as 50 meters due to railway lines, effectively isolate populations, leading to genetic bottlenecks. It also forces gibbon families into smaller and smaller territories. Researchers use bio-acoustic monitoring to study these changes. By recording and analyzing the gibbons' territorial songs, scientists can map their distribution and density without direct observation. The data reveals an area where territories are dangerously compressed. Where three families might have lived in a given area in the past, the fragmented forest can now only support two, leading to increased conflict and stress on the animals.
💡Fun Facts
The western hoolock gibbon is the second-largest of all gibbon species, after the siamang.
A gibbon family group's home range can vary widely, from around 20 acres to over 150 acres, depending on the availability of fruit.
Males and females engage in complex morning duets that can last for up to 20 minutes and are used to defend their territory.
Gibbons sleep in a distinctive hunched position, tucking their knees to their chest and wrapping their long arms around them.
The forests of Karbi Anglong are not a formal tourist destination with set hours. Viewing gibbons is possible in protected areas like the Hoollongapar Gibbon Sanctuary, but requires a guide.
Admission
Entry fees may apply for national parks and wildlife sanctuaries in the region.
Accessibility
The terrain is hilly and densely forested, often without formal trails. Access requires good physical fitness.