Golden langur threatened by lack of suitable habitat

The golden langur, first photographed and formally discovered by naturalist and tea planter E. P. Gee in 1953 on the east bank of the Manas river on the Bhutan-Assam border, is now struggling for suitable habitats. A habitat suitability study of the golden langur, a primate that is endemic to Assam in India and the bordering country of Bhutan, projects that only 13% of the current habitat will be suitable for the species by 2031. At present, 18% of the current habitat range of 66,320 square kilometres across the transboundary region is suitable for the species.

Increasing habitat fragmentation and isolation across its range, especially in Assam, poses a danger to the golden langur, a primate species. Less than 8,000 individuals remain in the wild today in India and Bhutan; in India 80% of this population is outside protected areas.

Golden langur (Trachypithecus geei) belongs to a large group of Old World monkeys called the colobines (subfamily Colobinae). It has a restricted range in a transboundary landscape between Bhutan and India with diverse topography, and climatic and biotic components. It is listed among the world’s 25 most endangered primates. It was formally described by taxonomist H. Khajuria in 1956.

In Bhutan, the species is distributed in forested habitats of Tsirang, Sarpang, Zhemgang, and Trongsa districts, over 3,486 square km, which is about 9% of the area of the country. In India, fragmented and isolated populations of the species live in the Chirang, Kokrajhar, Dhubri, and Bongaigaon districts of Assam, across 3,950 sq km, which is about 5% of the area of the state. In India, the golden langur survives in the Brahmaputra valley in semi-evergreen forests, while in Bhutan, it occupies Himalayan broadleaf forests.

The study mapped the habitat suitability for the species across its entire distribution and projected its habitat suitability on the simulated landscape for the future (2031). The results predict that out of the total range extent of 66,320 sq km, only 12,265 sq km (18.49%) is currently suitable for the species, which will further shrink to 8,884 sq km over the next decade, by the year 2031, projecting a marked reduction in its range. These suitable habitats are scattered mainly and fragmented in the species’ southern range.

Lalit Kumar Sharma of the Zoological Survey of India, the study’s corresponding author, told Mongabay-India that most existing studies were only focused on smaller areas and mostly on population estimation and behavioural research. Fewer studies were available on the microhabitat details for the species.

“Our study on the species’ entire range regarding habitat details and future distribution range for the species is first for this endangered species. It is important to know the fate these animals face in the near future so that appropriate measures for conservation can be taken,” he said. “Our study found out that the species is more sensitive to the changes in landscape and patches rather than climate change.”

“The entire population of the species is also divided into two parts. One large continuous population in Bhutan and one scattered population in India within several forest patches. These forest patches are rarely protected and several times inadequate to support large groups. Due to lack of food, these groups venture into human-dominated areas or in crop fields looking for food and often get thrashed as retaliation or chased and killed by local dogs,” he added.

The present study suggests that golden langur is more sensitive to land use and land cover changes than bioclimatic factors. Rapid deforestation and illegal logging have wiped out most of the forest covers in the districts of Bongaigaon, Dhubri and Kokrajhar of Western Assam, leading to a fragmented landscape.

Increased number of patches were noted for the evergreen broadleaf forest, evergreen needle leaf forests, mixed forests, savannas and grasslands in the transboundary landscape. A decline in the patch numbers was noted for the deciduous forests. These patchy, less dense land use classes indicate clear signs of an increase in fragmentations in the landscape, leading to reduced habitat connectivity, disrupting the gene flow, and loss of rare alleles (reduction in genetic variation) supporting local adaptation and genetic fitness.

“Lower elevations and deciduous broadleaf forests have been matched in our model as the most suitable habitat for the species. However, primates are highly adaptive species, and most of the other forest types can be used by the golden langurs if needed. But adjustment takes time and the rate of habitat destruction or forest conversion within the species distribution range is much higher,” Sharma said.

“With more forests getting destroyed, each group will have a lower amount of forest patches and in smaller sizes which can result in a rapid population decline for the species,” he said. Rapid deforestation and illegal logging have wiped out most of the forest cover in Bongaigaon, Dhubri and Kokrajhar districts.

The study says suitable habitats found for the species are scattered and fragmented and are vulnerable because of increasing human-caused changes leading to deforestation. Approximately 2,297 sq km of the new area beyond the present suitable habitat will become liveable for the golden langur in the future. But most of these suitable areas are patchy and scattered in the southern range throughout Assam, which is most vulnerable because of increasing human changes such as agricultural and urban expansions leading to deforestation.

“At this moment a good number of golden langurs are living outside any protected areas in India, and they are facing the threats from these forest conversions, increasing conflicts with humans and are sometimes killed as a retaliation by the communities in remote areas,” Sharma explained, recommending that connecting each remaining habitat patch with enough trees would be the best thing to do right now.

“A vast amount of data is needed for proper conservation care for this species, but we don’t have the time to study and gather all that information. By that time, we may have already lost much of the population of this species which will be irrevocable. Providing the species with shelter and interconnecting the patches for gene flow should be prioritised, and this should be a task conducted by both the countries hand in hand,” he said.

He said behaviour changes in fragmented and continuous populations should be studied to observe the species’ adaptation capabilities and identify the most vulnerable populations within the species range.

“Bhutan still has a vast amount of forest intact, and therefore careful management can secure the Bhutanese population for the species easily. However, the Indian population of the species needs to be measured very carefully. Scientific details on species ecology and genetics should open a lot of keys towards conservation of the species,” Sharma said.

Hope in community conservation

“The scattered distribution and the fragmented population in the southern range is a matter of concern, and the distribution is influenced by the distance from the evergreen and broad-leafed forest patches,” Hillol Jyoti Singha of Zoology Department of Bodoland University told Mongabay-India. Singha is not associated with the study.

Singha said the study has pointed out that the current distributional range is also affected by human-caused changes, which the authors have linked to the decreasing forest cover in the future.

“The study, however, did not see the human perception about the species, which may also change. For example, it has been predicted that some of the presently occupied suitable areas will be reduced in size, but what if the attitude of the people surrounding the area remains positive for the conservation of the species, then what would be the population of the golden langur,” asked Singha.

Primatologist Dilip Chetry told Mongabay-India that habitat shrinkage and fragmentation are known major threats to golden langur. “This paper has predicted how habitat shrinkage and fragmentation will be a more serious threat for the golden langur in the near future. The paper has identified suitable habitats for future conservation initiatives.”

“However, the study has not given thrust on analysing the scope of restoring connectivity between suitable prime fragments to ensure the long-term conservation of the species. Some of the areas of occurrence shown in the map are outside the natural distribution of the golden langur. Moreover, the range of contraction and no change areas as shown in the map include areas beyond the species’ distribution range,” Chetry said.

“A study carried out two decades back showed that the golden langur distribution in Kakoijana reserve forest would last only for 60 years (study done on a particular model) but now the population there is increasing along with increase in green cover thanks to the positive attitude of the people,” he said.

Community conservation is helping the species in increasing its population in certain pockets in Assam. In Kakoijana reserve forest in Bongaigaon district of Assam, local communities involved in joint forest management committees in the surrounding villages are aiding conservation of the species by protecting the forests. They have an intricate relationship with the forest.

Recently, local communities living next to Kakoijana reserve forest had opposed the Assam government’s decision to notify the area as a wildlife sanctuary as they believed the protected area demarcation would infringe on their rights. The community had said in the memorandum that their “dedication and sincere efforts have yielded positive results in restoring the forest canopy from less than 5% to over 70% and the golden langur population from less than 100 to almost 600 now in more than two decades.” A total of 34 villages with a population of around 2000 people are located adjacent to the reserve forest.

“The situation can improve if the protected areas can be revived or protected with the active participation of people,” Singha said.

“Local communities are most helpful in this regard and have been proven effective in many areas of Assam. However, their involvement in active conservation programs is vital,” Sharma reiterated.

Banner image: The habitat of golden langurs in Assam is severely fragmented and patchy. Photo by Udayan Borthakur.