Whispering bats

A western barbastelle bat gives its echolocation calls more softly than many other aerial hunters

Western barbastelle bats in Europe typically ping out their echolocation calls softly enough to locate a moth for dinner before the moth hears them coming, says Holger Goerlitz of the University of Bristol in England.
It's the first documented case of a bat species outwitting its prey by quiet stealth, he and his colleagues say online in a Current Biology paper released August 19. The battle between bats and moths has become a classic system for studying the evolution of predators and their prey.
In searching for moths, barbastelles echolocate at about the 94 decibel level, roughly the equivalent of a busy highway, Goerlitz reports. This bat version of whispering is 10 to 100 times lower in amplitude than other aerial-hunting bats' echolocation calls. Those rank more in the range of jet engines and the vuvuzelas blaring at the latest World Cup, Goerlitz says.
People can't hear frequencies high enough to detect any of this bat racket "quite lucky for us," Goerlitz says.
To measure the loudness of the barbastelle calls, researchers needed to know how far away from a microphone a flying bat was when it pinged. So they set up a microphone array where bats swooped through at night. The slight differences in times that the calls took to reach different microphones let researchers figure out the bat's position for each of more than 100 calls.
This array also let the researchers answer the critical question of whether the barbastelle's softer echolocation was soft enough for stealth attacks on eared moths. Researchers restrained European moths called large underwings along the bat flight alley and monitored the activity of their auditory nerves.

Source: Science News