Bats can subtly adjust the frequency of the sounds they use to do echolocation to adjust to particularly cluttered terrain.
In a laboratory testing room filled with dangling plastic chains, bats wearing tiny, half-gram microphones were recorded flying through the obstacle course. When confronted with the forest of chains, the bats tended to reduce or increase the sounds they emitted by a few kilohertz. On their return flights, the path is clear and they stop tweaking their frequencies.
The researchers hypothesize that using multiple frequencies helps the bats resolve their environments faster than using single sound could allow.
“It’s all a matter of matching the broadcast to the echo,” said Mary Bates, a biology graduate student at Brown University and a co-author of the new study March 29 in the Proceedings of the National Academy of Sciences. “It’s a matter of ignoring or not processing the things that are going to interfere and doing this careful matching of sound to echo.”
The bats need data about the placement of the chains faster than the first round of echoes can provide, so they send out a second and third and a fourth batch. By changing the pitch of the noises slightly, the bats can differentiate between their different noises. Their brains then integrate those streams of sounds into a high-resolution 3-D map of the terrain.
Researchers have often marveled at bats ability to use echolocation even in very crowded environments or among many similar bats using their own sounds to resolve their environments.
“The navy is really interested in what we do because manmade sonar has come nowhere close to what bats and dolphins can do,” Bates said.
The frequency-shifting trick is one way that bats are able to echolocate while moving quickly, Bates and her lab leader, Jerry Simmons hypothesize. They also use the trick when dealing with interference from other members of their species, they’ve discovered.