Climate Change

Bats dying of heat stroke: Experts fear mass population collapse, zoonotic diseases

Live bats don’t cause harm as they’re immune to viruses, but their carcass coming in contact with domestic animals may increase the probability of zoonotic diseases

By Himanshu Nitnaware
Published: Thursday 20 April 2023
Indian flying foxes or fruit-eating bats can tolerate temperatures of about 40 degrees Celsius. Photo: Niranjan Sant.

On April 17, at least eight bats in Odisha’s Jajpur district died as a heatwave swept across the state, compelling forest officials to spray water to maintain temperatures and hydrate the remaining bats to help them survive.

The incident is not new, but scientists and experts fear that the increase in temperatures and frequency of heat waves due to climate change may result in a mass population collapse.

Also read: Winged wonders: We should not resent bats, because we need them

A large number of bats dying from heatwaves may also lead to ecological imbalances and increased spread of zoonotic diseases, according to experts.

Indian flying foxes or fruit-eating bats in India can tolerate about 40 degrees Celsius of heat. However, 42°C is their tipping point and the extreme temperatures make them vulnerable to death, said Rohit Chakravarty, a PhD student at Leibniz Institute for Zoo and Wildlife Research, Germany.

On April 17, the temperatures across the state were between 41.6°C-44.2°C, according to India Meteorological Department.

Instances of bats dying in alarming numbers from extreme heat waves had been reported in Australia and other countries, Chakravarty said.

“Bats require good shade to roost and control their body temperatures. They have no predators apart from humans who may contribute in multiple ways for their habitat loss. They live for about 15-20 years and produce one pup a year,” he added.

If the population collapses in large numbers due to extended heatwaves, it may affect seed dispersal and pollination, creating an ecological imbalance in nature.

“All animals including bats across India, Australia and South East Asia get impacted by extreme heat,” said C Srinivasulu, professor of Zoology and director of Centre for Biodiversity and Conservation Studies, Osmania University, Hyderabad.

Fruit-eating bats are large in size and have a higher metabolism. Their body heat increases when they become active, he said. These bats usually live under tree canopies. But they are more exposed to extreme heat in summer as India mainly has deciduous trees that shed most of their leaves during summer.

Srinivasulu told DTE:

When exposed to extreme heat, bats tend to cool their bodies by fanning themselves with wings. But in this process, their body heat increases due to higher physiological activity, negatively affecting their health and resulting in death.

The expert, who has been studying bats for the last 25 years, said the winged mammals also have a tendency to drench themselves in water bodies during summers.

Bats roost near water bodies and cool themselves in water. However, some bats living away from these waterbodies may be unable to access them. In such cases, they are deprived of the vital resource, he said.

As a coping mechanism, bats also roost in satellite colonies when their primary roosting area is no longer feasible, Srinivasulu said. However, old males and the young population who cannot find new places may be left with vulnerable locations. “There is a synergistic impact on the number of reasons why it leads to death,” he said.

If a mass population collapse occurs, the local population may go extinct, thereby affecting a 40-kilometre radius of the ecosystem, he said.

The expert told DTE:

The disappearance of population will stop seed dispersal and pollination contributed by them. Even if a population of 10 per cent is lost, it will take three-four years to recover the ecological loss. And if every year 10 per cent of population is lost, it will take a decade to revive the population.

Not just fruit-eating bats but their insectivorous counterparts are also affected by extreme heat, said Kranti Yardi, senior scientist at Naoroji Godrej Center for Plant Research, Shindewadi, Pune.

“Insectivorous bats living in caves often move to the interiors as heat intensifies. But we cannot rule out the possibility of such bats not getting impacted by heatwaves. In urban areas these bats live in old structures, heritage buildings, trees and dilapidated stone structures,” she said.

Insectivorous bats play a crucial role in pest control, Yardi said. “A bat consumes at least 1,200 insects in an hour and it feeds for about three hours in a day. This pest control mechanism is significant for maintaining ecological balance in agriculture and urban areas. If such populations collapse, the insect population will not be controlled naturally,” she added.

Also read: New health threat? Pathogens frozen in permafrost resurface as Earth heats up

Such cases have increased over the past four years, said Rahul Prabhukhanolkar, coordinator at the department of environmental science, Govindarama Seksaria Science College, Belgaum. Bats have died due to extreme heat in Ahmedabad, Nagpur, Odisha, Uttar Pradesh and other states in India. But there is no evidence of the rising incidences of bat deaths as there are fewer studies in this direction, he said.

However, a 2010 study conducted in the Purulia district of West Bengal revealed that 56 bats died in April, May and June due to extreme heatwaves. The study also indicated that bats showed higher instances of fanning and panting as temperatures soared.

The researcher said bats are important as seeds of certain plant species, such as ficus, jackfruit and banana, only germinate after passing through the digestive system of these mammals.

Besides, bats are hosts of a number of viruses. “A live bat does not harm as it is immune to such viruses it harbours. But if these bats die in urban areas and come in contact with domesticated animals such as cats, dogs and others, it may increase the probability of zoonotic diseases,” he said. 

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