ECHOLOCATION IN BATS AND WHALES
“Toothed whales use echolocation to sense objects. Whales send a high-pitched sound (usually a click sound). The sound bounces off the object and some returns to the whale. The whales then use the returning echo to determine the shape, direction, distance, and texture of an object” (1). Echolocation in a toothed whale starts with a series of low-frequency clicks (called a train) produced by the animal.” This train passes through the melon of the whale (a fat-filled organ in the head of the toothed whale that focuses the sound wave). The train of clicks is focused into a beam that bounces off objects and reflects (echoes) back to the whale”. “The echoed sound waves are received in the fat-filled cavities of the lower jaw-bone. These sounds are conducted through the bone to the ear and the brain, where the location of the object is interpreted. The whale can determine the distance to an object, its size, shape, the speed that the object is travelling, and its texture” (1).
Bats also use the process of echolocation in order to find their prey in the dark. Bats produce the sound by rushing air from their lungs past their vibrating vocal chords. “These vibrations cause fluctuations in the rushing air, which forms sound wave (sound wave is just a moving pattern of fluctuations in air pressure). The change in air pressure pushes surrounding air particles out and then pulls them back in. These particles then push and pull the particles next to them, passing on the energy and pattern of the sound. In this way, sound can travel long distances through the air. The pitch and tone of the sound are determined by the frequency of the air-pressure fluctuations, which is determined by the way you move your vocal chords” (3).
Some bats emit the sounds from their mouth, which they hold open as they fly and others emit sound through their nose. It's not fully understood how the bat's sound production works, but scientists believe that the strange nose structure found in some bats serves to focus the noise for more accurate pin-pointing of insects and other prey. In the case of most bats, the echolocation sound has an extremely high pitch. “The sound travels through the air as a wave, and the energy of this wave bounces off any object it comes across. A bat emits a sound wave and listens carefully to the echoes that return to it and processes the returning information in its brain. By determining how long it takes a noise to return, the bat's brain figures out how far away an object is” (3).
The bat can also determine where the object is, how big it is and in what direction it is moving. The bat can tell if an insect is to the right or left by comparing when the sound reaches its right ear to when the sound reaches its left ear: If the sound of the echo reaches the right ear before it reaches the left ear, the insect is obviously to the right. The bat's ears have a complex collection of folds that help it determine an insect's vertical position. “Echoes coming from below will hit the folds of the outer ear at a different point than sounds coming from above, and so will sound different when they reach the bat's inner ear. A bat can tell how big an insect is based on the intensity of the echo. A smaller object will reflect less of the sound wave, and so will produce a less intense echo. The bat can sense the direction in which the insect is moving. If the insect is moving away from the bat, the returning echo will have a lower pitch than the original sound, while the echo from an insect moving toward the bat will have a higher pitch”(3).
Whales use their tooth to locate their objects while bats use their mouth or nose to make the sounds. The mechanism that these animals are using is safer because they can sense how far an object is and they can also tell the direction in which the object is travelling.
1. Echolocation –Whale Glossary. [Internet] 2006 http://www.enchantedlearning.com/subjects/whales/glossary/Echolocation.shtml
2. Google definition: [Internet] 2006 museum.nhm.uga.edu/gawildlife/glossary/gawwglossary.html
3. How stuff works “How Bats Work”. [Internet] 2006 http://science.howstuffworks.com/bat2.htm