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A World of Echoes

July 29, 2011

Rheanna Sand

 

Everyone knows bats are the coolest little mammals. I mean, you don't see a "Naked Mole Rat Man" comic franchise raking in the bucks, do you? Bats have the best of both worlds - they're small and furry and get all the benefits of warm-bloodedness and a social lifestyle. Oh, AND THEY CAN FLY. And some of them are vampires.

Bats also revealed to us the phenomenon of echolocation, or being able to "see" the world using sound rather than light waves. The animal - whether it be a bat, a dolphin, or a blind human - produces a chirp or burst of clicks and listens to the returning echoes, which give clues about objects in the surroundings. Details like the position, size, and even surface features can be determined by the most sophisticated ears. While it's true that bats can use this "sonar" for social communication, they mostly use it to find food. Two research studies from this week's issue of Science highlight different aspects of this dynamic hunting and foraging behaviour.

The first study, authored by Mary Bates and colleagues, addresses one major problem in echolocation: how do you separate the "clutter" echoes from those of prey? Turns out that bats use different harmonics in their calls, which are sort of like octaves - higher and lower versions of the same note. The second harmonic is beamed more weakly to the sides than to the front, and by comparing the echoes of the first and second harmonics, brown bats can make a pretty good guess which come from leaves blowing in the wind and which signal that tasty butterfly at 12 o'clock.

The second paper looks at another problem, this one specifically for nectar-eating bats: what does good food sound like? Bees and flies can use light cues in the visible and ultraviolet range, making flowers appear like bright beacons in a sea of grey. Bats cannot exploit these cues, but Ralph Simon and others have discovered that a species of vine, Marcgravia evenia, seems to have adapted a dish-shaped leaf right above the flower that amplifies the bat calls, making them stand out acoustically like beacons in a sea of echoes.

And those little tidbits can be added to the growing list of things that make bats the coolest little mammal on the planet. Take THAT, Naked Mole Rat Man.

*shudder*

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