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In “Bio-sonar: Toothed Whales and Bats Use Similar Acoustic Behavior to Hunt” we reported on research that deepened scientists’ understanding of how toothed whales use bio-sonar to hunt prey. Now, researchers in Hawaii working with a trained false killer whale named Kina report that she adjusts her hearing when she anticipates a loud noise.
Researchers attached sensors to Kina’s body that measured electrical activity in her brain as it responded to sound. Then they played a harmless beep followed by a five-second pulse of 170 decibels, roughly equivalent to the sound of a rifle being fired three feet away.
Over time, Kina turned down her hearing sensitivity when she heard the beep, seemingly fine-tuning it in anticipation of hearing the louder sound. Lead researcher Paul Nachtigall of the University of Hawaii says that echolocating marine mammals might have evolved this rapidly adjustable hearing to protect themselves from their own clicks and buzzes.
“The sounds they produce are very loud and then they must listen immediately for very quiet echoes," Nachtigall says. Over time, Kina changed her threshold of hearing by 15 decibels — “the equivalent of sticking your fingers in your ears,” says Natchigall.
Researchers hope their findings can be used to help avoid the damage caused to marine mammals’ hearing by man-made noise. “If loud sounds that apparently bother animals are preceded by a warning signal, and wild animals have the opportunity to quickly learn that the warning signal means here comes the big sound, then this could be used to mitigate the effects of loud sounds on wild whales, porpoises and dolphins,” Natchigall says. “It is very promising, but it’s only the beginning.”
