Some bats prevent crossed signals when flying with others by shutting down their natural sonar, new research reports.
Bats measure distances, dodge objects, and locate prey by listening to their own sound signals bounce off objects.
"Flying mute" could signal active cooperation among the mammals, but scientists don't know for sure.
The researchers made the surprising discovery while tracking how groups of captive big brown bats adjusted their signals as they pursued prey.
Some simply shut down their sonar for up to 800 milliseconds, according to Cynthia Moss, of the University of Maryland's Auditory Neuroethology Laboratory, and colleagues.
"To humans that sounds very short, but bats operate on a completely different timescale," Moss explained.
"[The time] from detection of an insect to capture is often less than a second. Typically when they approach an insect they [wait] only 20 to 50 milliseconds between sounds. So if they go silent for 600 or 800 milliseconds, that's a long time for them."
The study was published in Proceedings of the National Academy of Sciences.
Evidence of Bat Teamwork?
Biologist Richard Holland of the University of Leeds, U.K., said the exciting finding appears to show bats using "passive listening" to hear the calls of other bats.
"There has been a lot of speculation that they could do this, but I think this is possibly the first demonstration that they are listening to other animals' calls in addition to their own," said Holland, who was not involved with the research.
So far scientists have only theories to explain the behavior.
"When one bat went silent it was typically trailing another bat so it was in a good position to listen to the echoes and vocalizations produced by the leading bat," Moss said.
"But whether they are cooperating is an open question."
Both Moss and Holland suggested the behavior may help explain some longstanding bat mysteries.
"We see spectacular emergences like Carlsbad Caverns where millions of bats are emerging every night [and ask] how on Earth can they all be taking notice of their own echolocation call?" Holland said.
"Well, maybe they are not. That's a distinct possibility."
(See video of the Carlsbad Caverns.)
Though bats without sonar are flying deaf in a sense, they likely have ways to compensate, Moss explained.
"In the wild they could rely on spatial memory in familiar surroundings, and they could also use vision in moonlight that would aid them in locating obstacles," she said.
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