March 23, 2012

Whales Can Focus Echolocation Clicks

In the dark world of the underwater ocean, whales need to locate their prey accurately and quickly. In low-vision conditions whales use echolocation to find fish swimming nearby, and now it has been discovered that they can focus their acoustical “vision” to accurately located slightly differing objects.

For this study, Laura Kloepper from the University of Hawaii and her her PhD supervisor, Paul Nachtigall, utilized the help of Kina the False Killer Whale, a species related to dolphins. Kina is extremely adept at working with marine biologists after decades of dedicated work by Marlee Breese and her training staff.

For this series of tests the researchers trained Kina to recognize a 37.85 mm wide cylinder with a wall thickness of 6.35 mm using echolocation. She was then to push a button for a reward.

The research team then added two other cylinders still 37.85 mm wide but with differing wall thicknesses. One cylinder had a wall thickness of 7.163 mm and the other, being marginally thicker than the original cylinder, was 6.553 mm thick. Kina had to stay still in order to reap her reward when she recognized these cylinders.

Over several weeks the cylinders were randomly presented to Kina at distances ranging from 2.5 meters to 7 meters. Her echolocation clicks were recorded during these sessions using an array of hydrophones located between her and the cylinder.

Laura Kloepper, who led the study said, “By recording from several positions, we´re able to image the shape (and size) of her beam.”

The researchers discovered that Kina was changing the shape and size of her acoustic beam. She made the beam area wider when she was having difficulties distinguishing between the 6.553mm and 6.35mm cylinders.

The scientists speculate that when this wide-area sound was created, the whale´s melon acted like a responsive acoustic lens focusing the sound energy toward the object of interest. “It makes sense because echolocating is how [these animals] make their living, and during deep dives, they have very little light. So this means they can follow and track fish just by using sound,” says Kloepper.

Dr. Paul Nachtigall reported that Kina not only was focusing the sound, but was changing the sensitivity of her hearing. Kina was able to utilize super-sensitivity for her hearing, but she was also able to plug her ears to filter out potentially damaging loud noise.

The report can be found in the Journal of Experimental Biology.