Bats find their way around at night by emitting noise and listening to the way it bounces back to them. But since bats often congregate in large groups, how do they keep from losing their own signal in the din? A new study found that they do this much in the same way children do: by trying to screech the loudest.
Researchers at Tel-Aviv University wondered how echolocation could possibly be effective, given the fact that bats share the night with lots of other bats, who are presumably are also making ultrasonic noises. They performed a quick experiment and published their findings in the Proceedings of the Royal Society B.
Ethical and scientific considerations precluded them just shoving a bunch of bats in a room and seeing how things went. Apart from the chance of a bat getting injured, they had to make sure that the only stimulus that any one bat had to contend with was the sound of another bat. They trained bats of the species Pipistrellus kuhlii — a common insectovorous species — to land on a special feeding pedestal. Then they hit them with bat calls from 12 speakers throughout the room.
Bats didn't have any problem with their sense of echolocation getting "jammed." Bats wouldn't have made it this far if they couldn't be in proximity to other bats. (Mating, especially, would have been a nightmare.) What was interesting was how the bats responded.
Faced with too much noise, the bats made their calls louder. Researchers had thought that they might vary their call's frequency — screeching higher when they heard low-frequency calls and lower when they heard high-frequency calls. Actually, the bats made higher frequency calls no matter what.
The scientists believe that "the bats' response aimed to increase the signal-to-noise ratio and not to avoid spectral overlap." When they hear loud, high screeching, they're not going to try to change their tone. They're going to be the loudest, highest screecher of all.