dolphins pump down the volume

Just like bats (and submarines), dolphins send out sonar signals to navigate as well as home in on prey. They emit high-pitched sounds and then process the echoes that are bounced back from distant objects to obtain a picture of their world. But the problem is, as they get closer to their target, the echo comes back not only faster, but louder, so loud that it could become literally deafening. Bats can decrease the sensitivity of their hearing by flexing their inner-ear muscles to cope with the problem, but dolphin ears are less adaptable. So, how do dolphins keep from going deaf? Whitlow Au and Kelly Benoit-Bird from the University of Hawaii’s Institute of Marine Biology may have solved the mystery. In the June 19 Nature, they report that instead of turning down their receivers, like bats, dolphins can adjust the volume of their sonar clicks as they approach a target.

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 6/24/2003.