Bats can Focus Biosonar by Stretching Mouths

While in Cockpit Country for our first expedition to Jamaica looking for the Golden Swallow, John, Justin and I watched in awe as hundreds and hundreds of bats flowed out of a cave and flew in a distinct path right by us over the course of half an hour. The slightly shoddy video below can only partly convey the sensation of having the flapping mammals zoom past in a steady stream. We’ve recently featured a couple stories of scientific developments in bat research on the blog, including wing-beat echolocation in fruit bats and singing for communication in other species.

A couple weeks ago, we learned via Discover Magazine’s science blog by Elizabeth Preston that researchers in Israel have found that bats can also adjust the scope of their biosonar by changing the width of their mouths:

[Bats] 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.

You can read the rest of the original blog article from Inkfish here.

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