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Planet Earth

To Zoom In, Bats Say "Ahh!"

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In the future when touch screens are obsolete and we control our devices by facial gesture, maybe we'll zoom in and out the same way a bat does it. We'll open our mouths wide to narrow our field of focus. To see the bigger picture, we'll purse our lips tightly. But while we'll only be reading the news or shopping online, bats are operating one of the coolest sensory systems owned by a mammal. An Italian priest, Lazzaro Spallanzani, sent blindfolded bats through obstacle courses in the late 18th century and concluded that they seemed to use sound to navigate. But no one figured out how it worked for another century and a half. The 1835 British Cyclopaedia of Natural History attributed bats' navigational skills, a bit vaguely, to "delicacy of sensation." Now we know bats make sounds that are too high for us to hear. They navigate and search for food by listening to how those sound waves bounce back. They can adjust the length and rate of their sound pulses to gather exactly the information they need about their environments. And, researchers in Israel say, bats can widen or narrow their field of view by simply stretching out their mouths. Yossi Yovel and his colleagues at Tel Aviv University studied a bat called Bodenheimer's pipistrelle, or Hypsugo bodenheimeri. In the wild, the researchers observed bats coming to a small desert pond for a drink of water. On their approach to the pond, bats had to fly through a confined space before entering a more open one. The researchers set up an array of cameras and ultrasonic microphones facing the pond. The microphones let them measure the width of the sound beams that bats emitted during 312 flights. Then they used the camera images to estimate how wide each bat's mouth had been open at different moments. (This calculation wasn't easy, so the researchers assigned the task to an artificial neural network, which they trained using stuffed bats from a museum collection.) Yovel saw that as bats flew through a confined space, they used a focused, narrow beam of sound. When they entered a big, open space, they used a wide beam to zoom back out. The bats made the adjustment by changing the width of their mouths. Counterintuitively, a wider mouth creates a narrower sound beam for these bats. To zoom in from the broadest to the narrowest view, bats stretched their mouths more than four times as wide. The researchers also sent bats through a tunnel—like Spallanzani minus the tiny blindfolds—to make sure their results weren't specific to bats getting a drink of water. They saw the same thing as before: in a small space, bats gaped their mouths wide to zoom in. They did the opposite in a large space. Plenty of animals can change their gaze to direct their attention where it needs to be, or adjust the focus of their eyes from nearer to farther away. But no other animal is known to adjust its whole field of view like the bat does, Yovel writes. That might make bats a worthy animal to emulate for our future computer interfaces. We'll just have to make sure to stay engaged, because yawning at our desks would make things difficult.

Image: by Michael Sale (via Flickr)

Kounitsky P, Rydell J, Amichai E, Boonman A, Eitan O, Weiss AJ, & Yovel Y (2015). Bats adjust their mouth gape to zoom their biosonar field of view. Proceedings of the National Academy of Sciences of the United States of America PMID: 25941395

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