The sloth bear (Melursus ursinus), one of the eight species of ursids and among the most dangerous wild animals in the Indian subcontinent, is aggressive towards humans due to its evolution alongside predators that are now extinct as well as extant Bengal tigers. A careful study of its behaviour during encounters with tigers can help people across South Asia avert deadly attacks, three scientists have suggested.

Thomas R Sharp, David L Garshelis and Wesley Larson also suggest a number of ways for people living or working in habitats occupied by sloth bears to avoid lethal encounters.

This strategy would be helpful not just for people but also bears. This is because people’s adverse reactions to sloth bears have been one of the largest obstacles to their conservation.

They have also been one of the paramount reasons for sloth bears to categorised as Vulnerable on the International Union for Conservation of Nature Red List, the scientists stated in their recent study.

‘An enigma’

The sloth bear is somewhat of an enigma among the world’s eight bear species — the others include the brown bear, American black bear, Asiatic black bear, sun bear, polar bear, spectacled bear and the giant panda.

The bear mostly feeds on insects, especially termites and ants, as well as various seasonally available fruits.

“Of the eight species of bears, sloth bears, along with giant pandas (Ailuropoda melanoleuca), are at the very low end of the spectrum of carnivory; however, whereas giant pandas are unaggressive toward humans, sloth bears are highly aggressive,” the authors noted.

They backed this statement by comparing the attacks by sloth bears to those by other species. Some 7-8 per cent of sloth bear attacks are fatal. In comparison, 14 per cent of global brown bear attacks (the species is found on three continents — Asia, Europe and North America) are fatal.

“However, the sheer number of sloth bear attacks is remarkable, especially for a species whose diet is primarily termites, ants, and fruits,” the authors said.

Brown bears, which range across 44 countries, are commonly thought of as a highly aggressive and feared bear species in many parts of their range. But sloth bears, which are responsible for a much higher number of attacks, have not gained a similar reputation, except on the Indian subcontinent.

“Tallying all large carnivore attacks on people worldwide between 1950 and 2019, Bombieri et al. (2023) reported that sloth bears far exceeded all other species, including tigers (Panthera tigris),” the study stated.

One reason for the sheer magnitude of fatal attacks, according to the experts, is that large human populations reside near or use sloth bear habitats.

Roughly 90 per cent of sloth bear range is in India (though it is also found in Nepal, and Sri Lanka). Dense human populations live in India’s villages, adjacent to sloth bear habitat. Hence, sloth bear–human encounter rates are high.

Evolutionary defence mechanism

The authors posited that the aggressive nature of the sloth bear toward humans may be related to its evolved defensive behaviour toward tigers and other (now extinct) large predators.

“Bengal tigers (P. t. tigris), the subspecies of the Indian subcontinent, may be twice the size and weight of a sloth bear, and represent a considerable threat. In some tiger parks in India, up to 2% of tiger scats include sloth bear remains. While sloth bears are occasionally predated upon by tigers, they are also well known for surviving tiger encounters by aggressively fighting off their would-be killers, as has been documented in various accounts since the 1800s,” the study read.

The authors collected and examined 43 videos or photo documentations of sloth bear-tiger interactions posted on the internet or social media from 2011 to 2023, mainly by tourists visiting tiger parks — Ranthambore National Park, Tadoba Andhari Tiger Reserve, Nagarhole National Park, Kanha Tiger Reserve, Pench Tiger Reserve, Bandhavgarh National Park, Sariska Tiger Reserve, and Jim Corbett National Park.

An analysis of the collected material revealed that sloth bears were most likely to stand up and charge if they first became aware of the tiger at close range (less than 3 metres away).

“This aggressive–defensive strategy, intended to dissuade the tiger from attacking, appeared to be successful, in that 86% of interactions ended with no contact, whereas four (9%) culminated in the bear’s death,” the authors wrote.

They also proposed another reason for the sloth bear’s aggression. The bear is ‘myrmecophagous’, feeding on a diet rich in termites and ants.

Its long, blunt front claws, well adapted for digging termites and ants, hamper its ability to climb trees for escape. Sloth bears walk with their head down, focused on scents underground, and make considerable noise digging and blowing soil, enabling tigers to approach quite closely without being detected.

Important advice

But what may be true for a tiger, may not be true for a human. Like a tiger, a human can also approach (albeit unknowingly) a slot bear without being detected.

Thus, people living or working in habitats occupied by sloth bears should try to avoid close-range encounters by making noise. If, however, a person does encounter a bear at close range, and the bear has not noticed them yet, it is best to back off quietly, so as not to draw the bear’s attention.

If, however, the bear has noticed a person at close range, it would charge, as it does in the case of tigers.

In such cases, a person should not try to run. For while a tiger can outrun a sloth bear, a human can’t. It is best to fall to the ground, cover up, and play dead. Unlike brown bears, a sloth bear will not eat a human being if it assumes the person is dead.

A sloth bear does not charge multiple tigers. Similarly, it is best to be in groups if you are in sloth bear habitat since it intimidates the bear.

Explosively charging and attacking a potential threat has served sloth bears well for hundreds of thousands, if not millions, of years, said the authors.

They call it ‘overestimating risk’. Charging and attacking a tiger (or human) can help them survive, whereas underestimating the risk may result in their death.

A most aggressive bear: Safari videos document sloth bear defense against tiger predation has been published in the journal Ecology and Evolution.

Simply Put: Displaced by development