Simmons and his colleagues conduct their research out of the bat lab, a suite of rooms in a basement laboratory at Brown University. They work with big brown bats, Eptesicus fuscus, which are commonly found in household attics, forests, and caves across North America and Europe.
The bats are relatively inexpensive for the researchers to keep in captivity and study. The knowledge the researchers gain about bat sonar is tested out on dolphins and applied to human sonar systems.
"We do experiments that measure how accurately they determine the timing of echoes and how they form images of scenes," said Simmons.
Bat lab experiments have shown that the animals are able to differentiate between sounds that are 2 to 3 millionths of a second apart, giving bats the ability to tell the difference between objects and shapes that are separated by only about the width of a human hair.
This unexpected finding suggested to the researchers that the bats use their sonar for purposes greater than simply tracking their prey. To find out what bats actually do with their sonar, Simmons and his colleagues filmed the animals with an infrared camera.
The camera recorded the bats body heat. Footage captured by the researchers showed bats zipping across the sky like comets, said Simmons. Their movies highlighted the bats' ability to navigate around the full range of objects in their environment, including trees and bodies of water.
"We see them doing things never imagined," said Simmons. "They spend a lot of time doing dogfights chasing each other."
The knowledge learned from these studies is being used by the Office of Naval Research to build a better sonar system.
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