‘Bat accelerator’ unlocks new clues to how these animals navigate

Bats are impressive navigators. Like so many sonar-equipped mini submarines, they deftly navigate dark forests and caves listening to the echoes of their own calls. But how bats can determine which echo to follow while flitting in a sea of ​​overlapping and competing signals echoing across the myriad surfaces of their environment has been a mystery until now.

In a new study published in Proceedings of the Royal Society B, Researchers demonstrate that bats find their way by listening to how their own movements change sounds.

Imagine being at a party with hundreds or even thousands of people talking at the same time; it’s difficult to single out a single speaker, says Marc Holderied, professor of sensory biology at the University of Bristol in England and author of the study. This is comparable to what a bat may face when the animal zooms around a dense forest – a chaotic environment that can make echolocation difficult.

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To solve this problem, animals appear to rely on Doppler shift, or how the pitch of a sound changes as a bat moves.

“When the bat moves,” Holderied explains, “this Doppler shift, in this complex echo of thousands of reflectors, carries information.”

How the team reached this conclusion is an impressive and strange story. Holderied and his colleagues observed wild pipistrelle bats using a contraption they dubbed the “bat accelerator.” The machine is essentially an eight-meter tunnel of conveyor belts covered in plastic sheets, about 8,000 of which are hand-stapled, says Athia Haron, a research associate in medical engineering at the University of Manchester in England and co-author of the study.

The researchers hypothesized that if the bats picked up on the Doppler effect, the direction in which the foliage conveyor belt moved would affect the animals’ flight speed.

When the conveyor belt moved in the direction the bats were flying, the creatures accelerated. However, when the foliage seemed to be coming towards them, they slowed down. “We made them believe their speed was different,” says Holderied.

The results suggest that bats take into account the Doppler effect when flying and use it to control their speed.

Researchers already knew about some species of so-called Doppler specialist bats, Holderied says, but pipistrelle bats are not among them. The new findings indicate that the Doppler effect is used by bats that are not Doppler specialists.

And this bizarre experiment could help engineers improve navigation systems for drones or self-driving cars, Haron says – something she has already started exploring. “If this comes to fruition, it would benefit many navigation systems that fail in these kinds of cluttered environments,” she says.

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