Photograph by Nature Photographers Ltd/Alamy



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A flying bat, such as this serotine bat, relies on bouncing high-pitched calls off of objects in front of them to navigate and find food.

Photograph by Nature Photographers Ltd/Alamy



Climate Change Affects Ultrasonic Bat Signals For Better, Worse

A shifting climate will change the fortunes of bat communities around the world, for better and worse.

Although bats are nocturnal, they’re hardly flying blind. Most bats see with sound thanks to echolocation: They emit ultrasonic calls that bounce back off physical objects in front of them.

Echolocation allows bats to stalk their insect and plant prey and also keeps them from flying into houses, trees, and telephone poles. (Watch a video comparing humans and bats that use echolocation.)

But a changing climate could hamper the ability of some bat species to hunt effectively using sound, according to a new study.

Evidence already suggests climate change may shift bats' geographic ranges and hibernation cycles. Now, alterations in the temperature of bat habitats could affect their echolocation abilities. (Read about "Bat Crash" in National Geographic magazine.)

Most bats emit ultrasonic calls between 12 to 200 kilohertz, while human hearing tops off at the bottom end of that range.

When sound waves from a bat call travel through air, their intensity gets fainter, or attenuates. Humidity, pressure, temperature, and the frequency or pitch of the call all influence attenuation.

"Bats calling at low frequencies will hear echoes from an object further away than bats calling at high frequencies," says study co-author Holger Goerlitz, a biologist at the Max Planck Institute for Ornithology in Germany.

A Warmer World

Goerlitz and his colleagues decided to examine how rising temperatures would affect bat echolocation, and their results are published today in the Journal of the Royal Society Interface.

Knowing how much the fading of echoes will change helps researchers predict how much prey a bat might be able to detect. Based on estimates that global temperatures will increase by between 3° to 7° F (2° to 4° C) over the next century, the researchers compared potential changes in temperate Germany to tropical Malaysia.

Whether the volume of space a bat can detect prey in grows or shrinks depends on variations in their own climate and call frequency, says Goerlitz.

Based on the researchers' model, bats living in temperate zones were more likely to lose prey detection volume, while in tropic zones, many bat species will actually be able to detect more prey. Bats calling at lower pitches generally gained prey detection space.

Adaptable Foragers

"This is a cool idea, and they have done a very thorough test," says Mark Brigham, a bat ecologist at the University of Regina in Canada who was not affiliated with the study. "But, it's hard to say exactly how their findings will play out in the real world."

That's because bat ecology is diverse, says Goerlitz, and their echolocation abilities aren't the only things that could determine how well they do.

One thing is clear: global warming will impact the pure physics of sound that bats use to echolocate.

But competition for food, how bats forage, and the affects of climate change on bat prey—these are all important factors. For example, bats flying over open air to forage for food rely more on hearing echoes over long distances.

Some bats will find more food and reproduce more, while others will struggle with picking up on fewer sounds from prey.

That could mean major changes for bat community composition, says Goerlitz, although it's impossible to pinpoint winners or losers in part because bats can adapt.

"If you're in a pitch black cave, you can recognize when the batteries on your flashlight are starting to get a little bit low. And what do you do? You put in new batteries," Brigham explains.

Many species of bats could probably recognize a decrease in their prey detection space, says Brigham, and just increase it by changing the intensity or frequency of their calls. (See "Bats Use Rolled-up Leaves as 'Trumpets'")