Have you seen the movie Finding Dory yet? In one of the many exciting sequences in the film, the protagonist Dory needs the help of Bailey the humpback whale to navigate through a maze of pipes. In a later, and even more exciting, sequence Bailey helps Dory keep track of a moving truck in which Dory’s friends Nemo and Marlin have become inadvertently captured.
Bailey, the beluga, performs these miracles doing what he does every day – seeing with sound. In fact, Bailey and other toothed whales and dolphins have evolved echolocation skills that are stronger than any man-made sonar. No wonder the movie makers chose to name Bailey’s exhibit “The World’s Most Powerful Pair of Glasses.” Whales and other marine mammals went back to the water and hence their hearing had to re-adopt to hearing under water. Echolocation is one of many interesting things about the auditory system of these species. For example, many of these species can hear up to or even above 100 kHz. But today we are extolling the virtues of echolocation.
Bailey and other marine mammals are not the only animals that use echolocation. Bats and even some cave-swelling birds use sound to see. Bailey and his other toothed whale and dolphin friends, however, have taken echolocation to significant levels of sophistication. The basic principle is the same as in man-made sonar—produce a loud signal and listen for it to bounce back from an obstacle. Basic distance and size estimates of the reflector can then be derived from the characteristics of the reflection.
Just distance and size though are child’s play for the expert whales. Whales and dolphins can not only discern distance and size of the reflecting object; they can differentiate between different shape reflectors. And we are talking about subtle differences here. Whales, working under positive reinforcement of getting a fish on a correct response, can learn to differentiate between a cylindrical and square metal rod a few inches wide. They have also demonstrated the ability to distinguish between reflectors of different textures and estimate the speed of moving objects. In other words, these animals probably do have the world’s most powerful pair of glasses.
So, when a whale produces a click for echolocation, it has no idea how far the click will have to travel before being reflected. So the wise thing to do would be to produce the loudest possible click—and so it does. Would that not put the whale’s hearing in danger? This is part 1 of 3, is it not? More next week.
Enjoy a brief clip on beluga whales and echolocation.
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