Dr Karl: Wiggling bat ears
BATS CAN NAVIGATE by listening for echoes. But they’ve evolved a subtle improvement on the basic concept, and it’s one we’ll almost certainly want to employ in the future.
Generally, bigger bat species eat fruit and don’t find food using sound, while smaller species eat animals, usually insects, which they find using echoes. We’ve known since the 1930s that these bats do this by emitting squeaks, then listening for echoes from these bouncing off objects they encounter, such as insects. If the bats receive an echo when their large, steerable ears are aimed in a certain direction, that tells them the direction of the insect. They determine the distance by measuring the time the echo takes to return.
But it turns out that bats also take advantage of what’s known as the Doppler effect. A typical example of this phenomenon occurs when we hear an ambulance siren, which is generating a note of a constant pitch or frequency. As an ambulance approaches, you hear the siren having a higher pitch, and when the siren passes you, the pitch is lower.
The prey of a bat, such as an insect, is usually moving. This changes the frequency of the echo that bounces off it. So now the bat has a third bit of information – the speed at which the insect is flying, as well as its direction and distance.
Then, in 2016, a mechanical engineer at Virginia Tech university in the USA, Professor Rolf Mueller, noticed something odd in photographs of bats. Often the ears looked fuzzy, while the rest of the animal was quite sharp and in focus. We already knew bats could move their ears up and down, and backwards and forwards, as well as shift the tips of their ears closer together or further apart. But Rolf found that bats were doing an entirely different movement. They were continually wiggling or vibrating different parts of their ears – mostly the outer parts. The extra Doppler information was coming from their moving ears and not their moving targets.
These recently discovered movements combine to give the bat even more information about their fastmoving next meal. It’s highly likely this information will flow on to help us in critical human situations, such as a drone delivering your next pizza.
DR KARL is a prolific broadcaster, author and Julius Sumner Miller fellow in the School of Physics at the University of Sydney. His latest book, Dr Karl’s Random Road Trip Through Science, comes with augmented-reality features and is published by HarperCollins Publishers Australia.
Follow him on Twitter at @DoctorKarl