Elephants can adapt to human habitation, but sirens stress them out

  • The stress responses of elephants from human-dominated plantations in the southern Western Ghats were not different from their counterparts in neighbouring undisturbed forests, showing that elephants can adapt to the presence of humans.
  • But in conflict situations, when humans aggressively drove away elephants using loud noises, they showed heightened stress levels, particularly for the younger age groups.
  • Such ‘drives’ should be avoided and conservation management actions should consider the physiological stress responses of elephants.

As more and more elephant habitats are falling under the ever-growing influence of humans, elephants are often coming into contact with people, whether they are passing through human-inhabited landscapes, or directly interacting with them, the latter of which sometimes culminate in intense conflicts.

But how do these iconic, endangered giants cope in human-modified habitats such as plantations? Are they stressed in the presence of humans, just like some of us are when we face them? And how do they react to negative conflicts with humans?

To answer these questions, researchers assessed the physiological stress responses of wild Asian elephants in the Western Ghats of southern India. Their findings were both promising and concerning. The good news is that the elephants appeared to adapt to human plantations; the bad news is that they were stressed after being aggressively driven away by villagers.

“While they could adapt to changing environments, we show that negative interactions such as drives can be a major cause of stress in these animals,” said Sreedhar Vijayakrishnan, a Ph.D. scholar at the National Institute of Advanced Studies, Bengaluru, and the lead author of the study.

Although past studies have looked at stress levels among wild Asian elephants, this is the first-of-its-kind to explore how elephants respond when they are aggressively driven away by humans.

Measuring the stress responses of elephants

It is not always possible to directly monitor the stress-related behaviours of elephants, says Vijayakrishnan. Also, some animals may not overtly display behavioural changes in the presence of humans. Consequently, his team measured the concentrations of glucocorticoids, a class of steroid hormones, in the faeces of elephants, which are released when the animals are stressed. Not only is this method non-invasive, “faecal glucocorticoid metabolite concentrations are a fairly reliable indicator of stress and is used across species,” explained Vijayakrishnan.

Fresh elephant dung close to a waterhole in the drier habitats of the Eastern slopes of the Anamalai hills, southern India. Photo by Sreedhar Vijayakrishnan.

During November 2013 to April 2014, the team scooped up dung samples from 69 elephants belonging either to herds, groups, or solitary individuals, living in two types of neighboring habitats in the Anamalai Hills: Vazhachal Reserve Forest, a relatively undisturbed evergreen forest, and Valparai plateau, consisting mainly of tea, coffee, and cardamom plantations, along with small forest fragments. Composed of a continuously connected network of protected areas, the Anamalais harbor the second largest contiguous population of Asian elephants throughout their entire range.

Each year up to 100 elephants use the Valparai plateau. While traversing the plantations, the elephants are sometimes driven away by residents. In these ‘drives,’ elephants are forced back “using tractors, trucks or other loud vehicles, sirens and other noise-making equipment” such as crackers, Vijayakrishnan described. “In Valparai,” he said, “it’s mostly done using vehicles and sirens.” His team compared the glucocorticoid levels before and after the elephant drives to understand how the elephants cope with these intense conflicts.

Elephant feeding on Ochlandra (Indian bamboo) inside a wet evergreen patch in the Anamalai hills, southern India. Photo by Sreedhar Vijayakrishnan.

Adaptation to human-dominated environments  

They found some encouraging results. In the absence of any direct human conflicts such as drives, the stress levels of elephants from the plantation-covered Valparai plateau did not differ from those inhabiting the undisturbed Vazhachal Forest Reserve.

According to Vijayakrishnan, this could be because of adaptation. “These elephants in Valparai have been using this human-use landscape for a long time,” he said. It has been more than a century since the plantation was established and it is likely that the elephants would have come across humans regularly. “In fact, several of these individuals were born in these plantations,” he noted.

Elephant herd feeding amidst a tea plantation on the Valparai plateau, Tamil Nadu. Photo by Sreedhar Vijayakrishnan.

This “interesting study” demonstrates that “elephants are one of those creatures that are very adaptive and, in fact, even seem to thrive in human-transformed habitats as long as they are not subject to direct threats and harassment,” said Raman Sukumar, professor at the Indian Institute of Science, Bengaluru, who has been studying human-elephant conflict for decades. “This gives some hope that elephants and people can co-exist, even if to a limited extent, which would contribute to the survival of this iconic species.”

“There is hope that the elephants in India can physiologically cope when the ideal—a large protected forest—is absent,” said Kathleen Gobush, a wildlife researcher at Vulcan Philanthropy and affiliate associate professor of biology at the University of Washington, who has studied the physiological stress response in African elephants.

“Like African elephants, the physiological stress response among individual Asian elephants varies significantly across age” and sex, noted Gobush. Adults had the highest levels of stress hormones among all of the age groups. And males had higher stress responses than females, a finding that has also been observed among African elephants.

Stress response soars after aggressive drives

But there was a worrying finding as well. The stress levels of the elephants shot up following the aggressive drives. Calves and sub-adults showed the largest increase with glucocorticoid concentrations spiking by 106 and 55 percent respectively, whereas adults displayed an increase of 24 percent.

This might be because adults are more experienced in dealing with these stressful situations than calves and sub-adults, said Vijayakrishnan. The younger elephants, he believes, are “perhaps learning to deal with these situations as they habituate to the changing environments.”  

Elephant feeding on jackfruits in the backyard of a house in a colony where tea estate labourers reside, in Valparai, Tamil Nadu. Photo by Sreedhar Vijayakrishnan.

If such drives are prolonged, it poses a threat to their fitness and survival because they can cause consistently high levels of stress, known as chronic stress, which can disrupt immune responses, digestive processes, and the reproductive system, explained Vijayakrishnan.

As a result, he calls for such prolonged drives to be avoided, stressing that “any invasive management action such as drives, translocation, and capture should take into consideration the behaviour and physiology of the animal involved.”

“Proactive steps, such as discouraging elephant drives, minimising human-induced disturbances or facilitating the free movement of elephants could help reduce stress in affected populations in increasingly altered landscapes,” the team concluded.

“Examining the reproductive success of female Asian elephants across a spectrum of human-dominated landscapes would be an important follow-up study for this endangered species,” suggested Gobush.

Vijayakrishnan cautioned that this study consisted of only six months and since elephants are long-lived species, they require long-term monitoring. “We have continued the work since then” and “we are also trying to look across habitat types and land-use types to see how variation in those influence stress hormone concentrations,” he said.


Vijayakrishnan S., Kumar M.A., Umapathy G., Kumar V., and Sinha A. (2018). Physiological stress responses in wild Asian elephants Elephas maximus in a human-dominated landscape in the Western Ghats, southern India. General and Comparative Endocrinology,  S0016-6480(17)30858-4. doi: 10.1016/j.ygcen.2018.05.009.

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