Echolocation is the use of sound waves and their reflected echoes to identify where objects are in space. Humans have developed analogous technology called sonar , which is short for so und n avigation a nd r anging. Humans use sonar for underwater applications such as mapping the sea floor, navigating waters safely, and identifying underwater objects such as shipwrecks or submarines. Bats, however, already possess biological sonar: echolocation! So, how does echolocation work? The bat emits sound waves from its nose or mouth and when the sound waves hit an object, an echo is produced.
The bat can then interpret the echoes to determine the size, location, and shape of the object. By constantly sending out these sound waves, the bat can quickly alter its course to intercept its prey. Bat echolocation sounds range from 9 kilohertz kHz to kHz, while humans only hear sounds between 20 Hertz to kHz. Both the different frequencies of the sound waves the bat emits and the echoes the bat receives provide information such as speed, direction, size, and position of the object hit by the waves.
The bats never flew straight toward the insects, the team noticed. They always swooped in from the side or below. That suggested that the angle of approach was key to sounding out their prey. And a microphone mimicked the ears. The scientists played bat calls toward a leaf with and without a dragonfly and recorded the echoes. By moving the bat head around, they mapped out how the echoes changed with the angle.
Bats used the leaves like mirrors to reflect sound, the researchers found. Approach the leaf head-on and the reflections of the sound beam overwhelm anything else, just as scientists had thought. But stand off to the side and the beam bounces off at an angle.
Much of the sonar beam reflects away, allowing bats to detect weak echoes bouncing off of the insect. Bats may even be able to distinguish between similar-looking objects.
Just how accurate? Other scientists are training bats in the lab to try to untangle how clearly they perceive shapes. Bats can learn a trick or two, and they seem to enjoy working for treats. Allen is training her bats to distinguish between two objects with different shapes. She uses a method that dog trainers use. With a clicker, she makes a sound that reinforces the link between a behavior and a reward — here, a scrumptious mealworm.
Inside a dark room lined with anti-echo foam, the bats sit in a box on a platform. But if the bat senses a cube, it should stay put. Allen tricks her bats with speakers that play the echoes that an object of that shape would reflect. Her experiments use some of the same acoustical tricks used by music producers.
With fancy software, they can make a song sound like it was recorded in an echo-y cathedral. Or they can add distortion. Computer programs do this by altering a sound. Allen recorded the echoes of bat calls bouncing off a real dumbbell or cube from different angles. When the bat in the box calls, Allen uses the computer program to turn those calls into the echoes she wants the bat to hear. That allows Allen to control what signal the bat gets.
Her experiment explores whether bats can do something most people easily do. Imagine an object, such as a chair or a pencil.
In your mind, you might be able to flip it around. She can go to the lab only to care for the bats. But she hypothesizes that the bats can discern the objects even when they view them from new angles.
The experiment also may help scientists understand how much bats need to inspect an object to form a mental image. Are one or two sets of echoes enough? Or does it take a series of calls from many angles? One thing is clear. In this recording, the pallid bat Antrozous pallidus makes both echolocation and social calls.
The audio is slowed down 10 times so the human ear can hear it, and the spectrogram below is a graphic representation of the sounds. This big brown bat's Eptesicus fuscus echolocation call sequence was recorded in Rio Blanco County, and the spectrogram is below.
In this recording, the big brown bat's echolocation call has a feeding buzz. The spectrogram is below. The spotted bat Euderma maculatum is actually faintly audible to humans with good hearing. Can you hear this echolocation call? This is another recording of a spotted bat's echolocation call, but it's 10 times slower so humans can hear it. The spectrogram, above, is the same for both. Explore This Park.
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