These bats beat the heat with a daytime dip in the lake

Unlike us humans, most other creatures don't enjoy the perks of air conditioning and refrigerators, so when a heat wave rolled into southern India last month, fruit bats had to find a natural solution to staying cool.

For more than two weeks in middle and late May, locals in Hyderabad spotted some peculiar behaviour in the resident bats. Normally nocturnal, the animals began emerging during the hot afternoon to fly in circles over the famous Hussain Sagar Lake. According to witnesses, the bats were in the habit of swooping down near the water, sometimes even touching the surface.

Srinivasulu Chelmala of Osmania University provided a straightforward explanation for this change in daytime habits: "When the temperatures are higher than average, the bats … display this unique behaviour," he explained to The Hindu newspaper. "[T]hey navigate to the nearest water body and soak their bellies, which is close to a dip."

The bats in this case were Indian flying foxes (also called greater Indian fruit bats), which are native to southeast and east Asia. During the day, the animals tend to gather up in the trees, forming huge colonies of hundreds of individuals. At night, they go out looking for the tastiest local fruits.

The flying foxes are also among the largest bats in the world, growing up to 1.5 kg (3.5 lbs) and with wingspans as wide as 1.5 metres (5 feet) across – watching groups of them swoop over the lake at dusk is quite a sight:

Brian Pope of the Lubee Bat Conservatory in Gainesville, Florida agrees with Chelmala that the bats' behaviour is a cooling-down strategy – though he's never seen it before. While fruit bats regularly visit freshwater looking for fruit or flowers, he told me, "usually when they skim the water's surface it's to get a drink."

Overheating can be a very serious problem for bats, especially during the hottest parts of the year in the hottest parts of the world. "When temps are too high, fatalities occur, especially for nursing [females], and older/immunosuppressed individuals," he said.

Taking a dip in a local lake is not the only strategy bats have for staying cool. For one thing, their habit of hanging out in trees (or caves, depending on the species) keeps them in the shade until the sun goes down. But when that fails, they can also use their wings.

"Bats use their wings for thermoregulation much the same way elephants use their ears," Pope explained. "There is an enormous blood supply in the wings and flapping helps to cool the blood down, which circulates to the rest of the body."

The bats in Hyderabad weren't taking full dips in the water (best to stay airborne for these manoeuvrable mammals), but if they did happen to splash down, they'd probably have made it back to shore – it turns out these animals are quite capable swimmers!

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Top header image: Chris Earley/Flickr