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Too close for comfort: Proximity to humans is significantly affecting the behaviours of lion-tailed macaques

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23 Sep 2020
Too close for comfort: Proximity to humans is significantly affecting the behaviours of lion-tailed macaques

The Lion-tailed macaque, an endemic species of primates in the Western Ghats. [Image credits: Ganesh Raghunathan]

Warning: This article contains images showing animal injuries that may be disturbing to some readers.

In the Annamalai hills of Valparai, Western Ghats, lives a species of primates found nowhere else on the planet—the lion-tailed macaques. For thousands of years, they have lived a life of frolic—jumping from tree to tree in the canopy of the rainforest and feasting on their favourite fruits. Everything changed in the last two centuries. Loggers cut down most trees in the pristine forest and turned them into commercial plantations. Soon, a small hamlet came up, which grew into a village, and now is a bustling little town with markets, hospitals and people.

Today, with the cherished homes destroyed, the lion-tailed macaque (Macaca silenus) is an endangered species, and barely a few thousand of them remain in the wild. “The last large-scale study, which surveyed the lion-tailed macaque population across the Western Ghats, estimated their numbers to be between 3000–4500 individuals,” says Ashni Dhawale. She is a researcher at the National Institute of Advanced Studies, Bengaluru, and has been studying these monkeys for the past five years.

In an in-depth study, which involved observing the antics of the macaques in the Puthuthottam area near Valparai, Ashni discovered something exciting and perhaps alarming in their behaviour. She closely followed one of the four groups of wild lion-tailed macaques that consisted of 26 individuals, every day for four months. She found that the monkeys showed many differences in their foraging behaviour and social interactions as they traversed forest interiors, coffee plantations, forest edges and human settlements. The findings of the study are published in the journal PLOS One.

Many animals, including monkeys, have shown changes in their behaviours in response to increased human interactions. In areas where tourists throng, studies show that rhesus macaques have altered their diet, feeding mostly on what visitors give them. In Bandipur, the bonnet macaques have been observed to stretch their hands out, asking for food from visitors to the park. Ingenious, you say? It may be perilous, argue researchers.

Most common species of monkeys, like the bonnet and rhesus macaques, have successfully adapted to changing landscapes. They are ‘generalists’ in that they can eat anything and live anywhere. But, lion-tailed macaques are different. They depend on the forest canopy to roost and find food. They feed on native fruits, and insects found only in the forests of the Western Ghats. The social organisation of the group is also different—it is made up of a single male and many females with a strict hierarchy. The presence of humans in their habitats, the study shows, has affected the macaques in unpredictable ways.

Tempting human-origin food—the bone of contention

In nature, the lion-tailed macaques spend significant time looking for food on the trees or among fallen leaves and barks on the ground. However, in areas with human presence, calorie-rich food, like fruits, vegetables, cooked or packed food, is easily available. This lure seems to have influenced their natural behaviour to a large extent. “We observed an overall increase in aggression (among males) and affiliation (among females) displayed by the lion-tails, in human-modified habitats,” says Ashni, on her findings.

A mother and her offspring forage on a Ficus tree [Image Credits: Ashni Dhawale]

In the hospital premises in Puthuthottam, one of the study areas with high human presence, the researchers found that the macaques spent less time foraging and more time resting. They were always on the lookout for humans, who may be carrying food. The researchers could not measure the components of their diets in human-dominated areas. However, they found that in open patches of the forests that had no canopy, the macaques mostly ate insects rather than fruits and other plant-based food.

Like most other primates, the lion-tailed macaques also have a strong social hierarchy within a group. There are dominant, intermediate and subordinate females. “This social hierarchy dictates most of their daily activities, including how they access food, their tolerance to each other and their movement,” explains Ashni. In natural habitats, dominant females forage the most and have first access to food. However, the study found that subordinate individuals fed more frequently than the dominant females in areas with human presence, disrupting the social order.

Ashni then turned to observe allogrooming—a social interaction among primates that depends on the social hierarchy. “Allogrooming is observed between pairs of individuals, mostly belonging to the same level in the social hierarchy, wherein an individual cleans another's coat and removes ectoparasites, like lice, and dirt. It also serves as a means of social bonding between individuals,” she details. The study found that in human-dominated areas, subordinate individuals spent more time grooming dominant individuals. The researchers believe that this behaviour could result in a better chance of procuring food as quid pro quo. However, while the macaques initiated grooming more frequently in these areas, they spent little time in actually grooming!

Human-dominated areas also disrupted the composition of family groups of lion-tails, just like in bonnet monkeys.

“In some human-dominated areas, the bonnets have begun to split up into smaller groups containing a single male and multiple females. A similar adaptation is seen in lion-tailed macaques, which now contain multiple males and females in a family group found in these areas—a previously unheard-of occurrence for this species,” points out Ashni.

The study also found that lion-tailed macaques were often fed by tourists passing through the forest edges. As a result, they now flocked around vehicles or tourists, bringing them too close for comfort for both humans and the macaques. It may also increase macaque–human conflicts, say the researchers. Lured by our food, these already-endangered macaques are becoming roadkills.

A pregnant lion-tailed macaque, who is a victim of a road accident. [Image Credits: Kalyan Verma]

The findings show how the endemic lion-tailed macaques have made the best out of their rapidly changing native habitats and designed novel strategies to interact with humans. While further studies are needed to understand what drives these responses at an individual level, the current findings can help guide conservation practices for this vulnerable species, some of which have started.

“We regularly engage with various local stakeholders, including the state forest department and plantation owners, and the NGO Nature Conservation Foundation, to ensure the long-term survival of the lion-tailed macaque,” says Ashni.

Have humans converted this ‘specialist’ species into a 'generalist' that can adapt anywhere? That is a million-dollar question!

This article has been run past the researchers, whose work is covered, to ensure accuracy.