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Black monkey under threat, or is it just stress?

Updated: Apr 29, 2021

Nagarathna Balakrishna

MSc dissertation

Pondicherry university (2017-2019)

Loud whooping calls echo across the morning forests as I excitedly stroll in search of the black monkey or ‘Manthi’ as they call it in the local language. As I arrive at the site from where the whoops erupted, my searching eyes are confronted with a blanket of mist that lingers longer than I want it to. A quick rustle of the leaves and a few cackles and jumps assure me of their presence, who appear to mockingly look down at me. As the mist slowly begins to clear, I crane to look up in the dark canopy and find the well-camouflaged group of Nilgiri langurs.

The study group would conceal themselves within the canopy of the forests.

For my master’s dissertation, I studied the behaviour and ecology of Nilgiri langurs located within Kalakkad Mundanthurai Tiger Reserve (KMTR) of the Southern Western Ghats, Tamil Nadu, India. I began my observations in January 2019 and carried on till mid-March, 2019.

Namukh is shown as a red dot within the map of KMTR

Unlike studies on birds, reptiles, amphibians, fish or even large mammals like ungulates, primate studies require close habituation to a point where their behaviour is unperturbed by our presence. Habituation is achieved by persistent following of the chosen study group (maintaining distance and avoiding surprise or sudden movements) and identifying individuals based on distinguishing features. This process generally takes a lot of time and the duration differs from species to species. In my case, it took almost a month for the langurs to ignore my presence and go on about doing their activities. It was only after this, that I started sampling their behaviour and daily activities.

Nilgiri langurs are found in the Western Ghats of India and occupy a wide range of habitats from low lying tropical deciduous forests to evergreen forests in the higher elevation hill ranges. Despite their adaptable nature and wide occurrence, they have been classified as vulnerable under the IUCN classification, due to a recent decline in their populations. Anthropogenic activities such as clearing of forests for fuelwood and timber, agricultural expansion and unprecedented poaching for their fur and meat, propagated by myths are major threats to their survival.

Nilgiri langur distribution in India. Map and range modified from Ashalakshmi et al 2014 and Karanth et al 2010

They are majorly forest-dwelling, arboreal (tree-living) species that are rather shy and wary of humans. Leaves form the basic component in their diet, along with which they consume other plant parts like stems, flowers, seeds and barks. They are highly social and are seen in groups of 8-11 individuals, comprising of a single male, multiple females and infants.

Earlier studies largely focussed on the behaviour and diet of Nilgiri langurs inhabiting relatively pristine forested areas while only a few have looked at the impacts of disturbances on their habitat and group dynamics. Therefore, I wanted to further understand the ecology and diet in response to habitat disturbances and see how it varied among individual members of the group.

A mother-infant duo along with another sub-adult female resting on a Wild Durian tree

The study site I chose was a slightly disturbed forest in Nalmukh, KMTR which was interspersed with Eucalyptus and cardamom plantations. The site was constantly frequented by humans for wood cutting and logging for fuelwood purposes. Nalmukh, literally means four faces/directions, and it was aptly called as four roads diverged from this point leading to four different destinations. Eucalyptus trees lined the edge of the field site which overlooked the road leading to adjacent tea estates, while a post office and tea stall nearby ensured regular human and vehicular movement. I selected a single group of nine individuals which comprised of one adult male, three adult females, two sub-adult females and three infants.

This is where it all started- The path that led to my field site, beside the post office.

Slinging my camera and binoculars on either side of my shoulders and strapping a bag with rolled up datasheets and a tiffin filled with hot steaming rice and rasam, I would leave for my field site at around 5:45 am along with my field assistant. I would follow the group of langurs and observe each of their activities from morning till evening and repeat the same for six days a week for almost two months. Each morning, I would find them munching on their favourite leaves at the same site from where I had left them the previous evening. Using a portable GPS, I also tracked their locations and estimated their extent of range within the field site.

Between January and March 2019, Nilgiri langurs moved around an area of 0.1 km² (Note: this range can change based on the availability of food)

The results showed that Nilgiri langurs spent a maximum amount of their time resting, followed by feeding and locomotion. The prolonged resting period has been largely attributed to the digestion and fermentation of their leafy diet. I recall an instance where I would be in a precarious position, on all fours, while following the langurs crawling through bamboo thickets, only to find them dozing off in the canopies. And this would go on for hours on most of the days.

Afternoons naps that last for hours together

They spent very little time in social activities such as playing and grooming. Playing was observed among and/or in between infants and sub-adult females while grooming was a characteristic of adult females and sub-adult females. According to Kavana et al 2015, the increased folivory (leaf-eating behaviour) and arboreal nature of Nilgiri langurs in comparison to Hanuman langurs (Semnopithecus hypoleucus) have shown to reduce their time for social interactions and therefore affect birth rates.

Adult female feasting on Wild Durian flowers

Wild Durian (Cullenia exarillata), a flowering evergreen tree species was abundant within the range of the langurs and was in a peak state of flowering during the course of the study. This explained the predominance and preference of its flowers in their diet despite being majorly leaf eaters. In total, they fed on the leaves, flowers, petioles, seeds, flower buds and barks of 34 plant species. This included the barks and leaves of Eucalyptus and Alder tree (Alnus nepalensis) respectively, both non-native introduced trees found along the edge.

A dehisced Wild Durian fruit with seeds exposed, a delicacy relished by the langurs.

An interesting observation was that they fed on the leaves of Lantana camara, an invasive weed that has rampantly spread along the forest edge, for which they would descend to as low as five feet above the ground (note that they are mostly canopy dwelling). This feeding observation on L. camara leaves has not been previously reported and thus adds to the long list of plants in their diet.

Lantana camara plant

Was the feeding on Lantana in response to habitat disturbance or another event of foraging on an abundant and available food source? Lantana camara is also known to have antimicrobial and fungicidal properties. Could it be that the langurs were feeding on it to prevent or treat an ongoing infection? Only further studies will be able to provide an answer for it. However, I am speculating that habitat disturbances and constant human movement within the field site might have elevated their stress, increasing their susceptibility to infections. And in turn, they fed on plants like L. camara to treat or relieve them of such infections.

Anthropogenic activities are rapidly changing global ecologies. This is true for all organisms, from the smallest microscopic bacteria to the large land and sea mammals such as tigers, elephants or blue whales. There is a great need for understanding how we are impacting plant and animal communities and their ecology to check our rampant activities and formulate management and conservation action plans before it is too late.

This study is not conclusive to show the effects of human disturbances on the ecology of Nilgiri langurs. However, it is critical to note that Nilgiri langur diet composition largely depends on the habitat they live in. Since they are a generalist species, that is, they feed on a wide variety of plant materials they are highly adaptable. This extent of adaptability will determine their survival and will largely depend upon how we protect and conserve our forests.


Contributed by Nagarathna Balakrishna. This work was carried out by Nagarathna as a part of her MSc thesis from Pondicherry university (2017-2019).


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