The capped langur (Trachypithecus pileatus), a leaf consuming primate with a particular ‘cap-like’ coiffure, is the second mostly seen primate in Assam after the rhesus macaque. As soon as thriving within the tropical rainforests of the Higher Brahmaputra Valley, the one colobine primate (characterised by their leaf-based weight loss program) within the area, is now in a precarious state of affairs.

The Valley was as soon as lined by an enormous lowland tropical rainforest. Nonetheless, through the years, agricultural enlargement, deforestation and growth of tea gardens have turned this forest into scattered fragments. These patches with settlements and fields at the moment are the final refuge for primates just like the capped langur.

A brand new research printed within the Journal of Asia-Pacific Biodiversity surveyed 40 rainforest fragments throughout six districts of the Higher Brahmaputra Valley between February 2019 and January 2020. Researchers discovered capped langurs in solely 11 websites, with proof that they’d disappeared from a minimum of seven forests the place they had been as soon as recorded, a decade in the past.

“By evaluating the surveys of the identical fragments, it grew to become clear that capped langurs have now disappeared from a number of of those areas,” stated Narayan Sharma, an writer of the research, and assistant professor on the Division of Environmental Biology and Wildlife Sciences in Cotton College, Guwahati. “This sort of longitudinal research helps us monitor not simply numbers but in addition their total incidence and distribution over time.” 

The capped langur has reported a 30% decline in its inhabitants globally over the previous 20 years, making it to the susceptible class of Worldwide Union for Conservation of Nature (IUCN), and in Appendix I of CITES. In India, it’s included in Schedule I of the Wildlife (Safety) Act, 1972.

In the course of the year-long survey, researchers recorded 82 langurs throughout eight websites, the biggest troop comprising 15 langurs in Hollongapar Gibbon Sanctuary. Even protected areas corresponding to Borajan-Bherjan-Padumoni Wildlife Sanctuary, beforehand house to the species, reported no sightings throughout this research.

Not less than one-third of the capped langur’s habitat in Assam has been misplaced for the reason that Eighties as a result of tree felling and encroachment.

Pradipta Baruah, Indian Forest Service (IFS), and subject director of the Orang Tiger Reserve, stated, “We see rhesus macaque populations multiplying in the identical atmosphere the place capped langurs are struggling. This means that one thing particular is affecting the langurs, and it requires long-term investigation to grasp the difficulty higher.”

A fragmented rainforest

The Higher Brahmaputra Valley is among the many final remaining lowland tropical rainforest zones in Northeast India, unfold throughout six districts: Dibrugarh, Tinsukia, Sibsagar, Charaideo, Jorhat and Golaghat. These rainforest fragments had been as soon as a part of an enormous, unbroken stretch of forests.

Nonetheless, deforestation, as a result of agricultural enlargement and the event of tea gardens, has damaged up these steady forests into smaller, remoted fragments. “Historic deforestation right here is just not a latest phenomenon; it started practically a century in the past,” stated Sharma. “As an illustration, the railway line that cuts by Hollongapar Gibbon Sanctuary was laid through the British period, round 90 to 100 years in the past.”

However these fragmented forests nonetheless host seven primate species, together with the capped langur, however lack of cover connectivity has left populations remoted in pockets.

For the research, the researchers analysed three components: habitat, panorama, and anthropogenic. “Our speculation was that the bigger the habitat, the better the probabilities of capped langur presence; the smaller the habitat, the upper the chance of their disappearance,” Sharma added. “In smaller fragments, meals sources are restricted, and this ecological constraint performs a serious position of their decline.

A drop in numbers

In 1989, when naturalist Anwaruddin Choudhury was finding out capped langurs for his PhD, he estimated their inhabitants in Assam at round 39,000. By 2014, that quantity had dropped to 18,600. Since then, no contemporary estimate has been made.

“What makes this worrying is that the capped langur is a forest-dwelling species,” Choudhury stated. “With forests changing into fragmented, these langurs find yourself remoted in separate patches, making breeding troublesome and finally inflicting their numbers to say no.”

The latest research additionally factors to an “extinction debt”, the place the implications of habitat loss should not fast, however are felt after a number of generations. Sharma famous that capped langurs are extremely adaptive. “These landscapes had been degraded way back, but it took many years for his or her populations to say no. That is what we’re witnessing at this time.”

Human pressures on the forests

Whereas looking is just not a serious menace on this area, oblique human pressures are. These embrace illicit logging, extraction of non-timber forest merchandise (NTFP), and lack of meals and roosting timber.

Numerous indigenous communities in Northeast India rely closely on forest assets and merchandise for his or her livelihoods, however extra extensively on NTFP, which play a major position of their subsistence and meals safety, states a 2020 research. With restricted revenue sources, locals broadly gather non-timber forest merchandise for private use or commerce.

An neglected menace is the elimination of saplings of meals and roosting timber from forest fragments, which prevents younger timber from maturing and reduces each meals availability and cover connectivity, each important parts of capped langur ecology and survival.

“Locals typically lower saplings for firewood,” stated Neeharika Gogoi, a co-author of the research and PhD scholar on the Division of Environmental Biology and Wildlife Sciences in Cotton College, Guwahati. “Over time, this prevents meals timber from maturing and reduces variety within the forest. One among our key findings was that capped langurs survive finest in fragments with excessive meals tree density.”

Logging is one other main stressor. “When the cover is damaged, langurs are pressured to the bottom, exposing them to predators and different threats,” Gogoi added. “Logging additionally removes fruit-bearing timber important to their weight loss program.”

As primarily leaf-eaters, capped langurs require a gradual provide of younger leaves, fruits and seeds. In degraded forests, some troops have been pressured into tea estates and villages to outlive.

“We discovered that meals tree density emerged as a very powerful predictor of capped langur presence,” Sharma stated. “Even in small forest fragments, if the density of meals timber is excessive, langurs can survive there for a very long time. Whereas many components affect their incidence, the provision of meals timber is the strongest determinant.”

Capped langurs in human-inhabited areas

The research documented capped langurs in Borajan and Chala Reserve Forest, the place they now forage, relaxation and even set up house ranges in human-dominated areas.

In Borajan, Gogoi initially noticed a troop of six langurs in 2019. By 2022, solely three grownup females remained. In Chala, simply two females had been noticed, transferring alongside a troop of rhesus macaques.

“With out males, they can not reproduce, and that group will seemingly grow to be regionally extinct, except males be part of them,” Gogoi stated, whereas citing examples of human-related disturbances such for instance the place a langur was killed by a rushing prepare, based on native accounts.

“In Borajan, there’s a presence of leopards, and pythons,” Choudhary stated. “Because of diminished tree cowl, langurs are pressured to maneuver to decrease ranges, and after they roost on small or degraded timber, they grow to be extra susceptible to predation. Different primates too have declined, although this pattern is exclusive to Borajan.”

The best way ahead

Specialists stress that the important thing to survival lies in habitat restoration. Defending and replanting native meals and roosting timber corresponding to Gmelina arborea, Dalbergia sissoo, and Albizia lebbeck may assist capped langurs maintain themselves.

“Though degraded, many of those areas are nonetheless underneath the Forest Division,” Sharma stated. “With collaboration between the [forest] division and NGOs, restoration may help capped langur populations get better.”

Researchers additionally suggest easing stress on forests by offering native communities with alternate options to firewood, corresponding to subsidised LPG and biogas.

Sharma additionally emphasised the position of the “matrix” or the areas surrounding fragments, corresponding to tea gardens, settlements, orchards, and paddy fields. “If the standard of this matrix is nice, langurs will use it,” he added. “However it shouldn’t grow to be extra resource-rich than the forest itself, or the animals might abandon forests for human habitats.”

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Learn extra: Species no bar: Langurs forge uncommon alliances within the wild

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Banner picture: A capped langur at Bordubi. Picture by Neeharika Gogoi.