Stress tests and drones: the new playbook to protect the endangered western hoolock gibbon

In the Hollongapar Gibbon Sanctuary in Jorhat, Assam, the endangered western hoolock gibbon, the only non-human ape species in India, compete to be heard over the thundering roar of a passenger train that passes through the reserve forest.

Walking through the 2,100 hectare sanctuary, visitors listen intently for the cacophonous vocalisations of the gibbon from the upper canopy while our guide points to a tall hollong tree that this forest is famous for and named after.

Soon afterwards, we hear a rustle as a family of gibbons, including two offspring, swing majestically overhead. Even as we watch in awe, a faint, more threatening rumble grows louder. The gibbons scamper through the trees, and the entire forest resonates with the deafening noise of a train on the British-era Northeast Frontier Railway line that splits the forest into two unequal parts.

The train typifies the multiple anthropogenic pressures, including habitat loss, fragmentation and hunting, that affects the western hoolock gibbon across its habitat in the northeast Indian states of Assam, Meghalaya, Arunachal Pradesh, Manipur, Nagaland and Mizoram. Such has been its decline over the last half a century that, according to estimates, the gibbon population has plummeted from over an estimated 100,000 individuals to less than 5,000.

Easy target for hunters

Like in most of their geographical range, the gibbon’s presence in Assam too has become severely restricted due to habitat loss and fragmentation. Additionally, threats like hunting have led to the species being listed as among the most endangered of primates in the world. The expansion of settled agriculture and deforestation too have eaten into the gibbon’s domain, say researchers.

While experts believe that 9 out of 10 gibbons have disappeared over the last few decades, an exact population count has been difficult to arrive at, says Divya Vasudev, Co-Founder and Senior Scientist at Conservation Initiatives, a non-profit based in Shillong. Gibbons are also secondary targets for hunters due to their loud vocalisations that can go on for up to 30 minutes.

The challenges faced by gibbons are emblematic of pressures on low-lying rainforests in Northeast India, says Rushikesh Chavan, Director of The Habitats Trust based in Noida. Chavan adds that changing land-use and jhoom cultivation are key threats to the species. “Previously, these cycles of slashing and burning would last decades, where forests would be destroyed and then allowed to regenerate. However, these cycles have now come down from decades to just 7-10 years due to pressures on the local communities themselves,” he says.

Studying genetics and stress

Despite challenges, initiatives are being undertaken to protect the gibbon. Udayan Borthakur, Director and Head of Wildlife Genetics Laboratory (WGL) at Aaranyak, a conservation NGO in Guwahati, says that gibbon populations have become “small and isolated” across their range. “We are trying to study source populations, which could be in the Garo hills, Dehing Patkai and even Hollongapar.”

Aaranyak is compiling genetic data of gibbon populations through faecal matter collected in forests to understand whether in-breeding and in-breeding depression are causes for concern. “Through these analyses, we are trying to identify the source populations. For instance, in Hollongapar, our research will show if this current population has increased from a smaller population of a few individuals or if they are descended from a larger pre-existing population,” he said.

WGL is also studying stress levels of gibbon populations in different areas, to understand whether hormones such as cortisol are higher in populations that are in closer proximity to human settlements and other anthropogenic pressures.

Tech-based solutions

The Habitats Trust (THT), along with Conservation Initiatives, is working on technology-based solutions to identify gibbons in any particular habitat. “One of the key challenges researchers face, especially with arboreal species like the gibbon, is that traditional methods like camera traps to estimate population are not feasible as the animals are almost always found in the upper canopy,” says Santhosh Pavagada, Programme Lead, Technology for Conservation at THT.

This necessitates the use of alternative approaches like bio-acoustics. Machine-learning models are being developed to identify gibbon vocalisation from recorders placed inside forests. “The model will help researchers by extracting gibbon vocalisations and will provide time-stamps to quickly navigate to areas of interest in each audio-file where a potential gibbon-call is being heard,” says Kishore P., an associate manager at THT.

Thermal drones are also being explored for the possibility of detecting gibbons in a landscape using a computer vision model. “This model can analyse 20-40 minutes of flight time, sift through the footage and identify gibbons,” says Pavagada.

With a little help from the community

Local communities too are becoming involved in the conservation of the species. “Since much of the gibbon’s habitat in the hill tracts of Northeast India is owned and managed by resident populations, it is imperative that these communities are involved in conservation efforts,” says Varun Goswami, Co-Founder and Senior Scientist at Conservation Initiatives.

Vasudev says there are over a hundred tribes, each with its own unique laws and customs related to forest conservation and hunting. “Some tribes prohibit the hunting of gibbons, but we need to bring more on board to ensure the protection of the species,” she adds. “The more villages we work with and the more people that show conservation support and ensure there is some forest secure on their lands, the better. The main thrust has to come from the community.”

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