Echolocation
Sarah Phinney

Sound waves are disturbances in the air pressure. The change in air pressure moves the air particles, and then those particles move, which causes the energy and sound to move. This is how sound used for echolocation moves through the air.

Echolocation is the process of locating objects by using the echos that bounce off that objects. The sound waves bounce off an object and start to move the opposite way, causing an echo. Many animals use this techinque to find food and to navigate around the world. Two well known animals who use echolocation are bats and dolphins.

Bats

Like humans, bats use thier mouths to make noise, but they also use thier noses. Sound waves are made by pushing air past the vocal chords. Bats, however, tend to push air past the vocal chords to cause a very high pitch. The bat is able to tell how far away an object is by calculating how long it takes for the echo to return. The bat is able to do all the calculations in its brain. Bats tell if the object is to the right or left by what ear the sound reaches first. Fold in the ear helps bats tell where the object is vertically. Echos coming from below or above will hit the outer ear folds at different points, causing the echos to sound differently when they reach the inner ear. The intensity of the returning sound is how bats tell how large or small the object is. The smaller the object the smaller the intensity, while the larger the objects the larger the intensity is. Using the Dopplar Affect, the bat can tell is the object is moving towards or away from it. If the echo's pitch is lower than the actual sound, the object is moving away from the bat. If the pitch is higher, the object is getting closer to the bat. Bats process all this information much like we process visual information. Bats do not only rely on thier sense of hearing. They also have an acute eyesight, so they use thier vision along with using echolocation.


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Dolphins

The way dolphins use echolocation is very much the same as bats use echolocation. Dolphins produce clicks, which makes the sound waves. These clicks pass through the melon. The melon is in the forehead of and is made of fats. It helps focus the sound waves into a stream that is sent forward in front of the dolphin. The speed of the sound waves produces by the dolphin move much faster than the sound waves produced by the bat. This is because the water molecules are closer together than the air molecules, so the disturbance is able to move much more quickly. 4.5 times faster to be exact. Dolphins use lower frequencies since the wavelengths are longer and they move farther. Since dolphins obviously don't have ears like a bat, the echos produces from the swim bladder in a fish are recieved in the fat filled lower jaw, then go to inner ear, where the sound is then transferred to the brain. The brain then interprets the sound so the dolphin can tell the size and location of the object. In this way, dolphins are much like bats. Again, dolphins use echolocation with vision, when using vision is available. Sometimes the ocean can be dark and murky, so echolocation is very helpful for dolphins. They do, however, find an object with echolocation when they are able to use thier eyes.

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References

http://www.inkokomo.com/dolphin/echolocation.html

http://askabiologist.asu.edu/echolocation

http://animals.howstuffworks.com/mammals/bat2.htm

http://www.seaworld.org/infobooks/bottlenose/echodol.html