Dolphins use small ear openings on both sides of their heads to listen to or hear sounds. These small openings are what they would usually use for hearing when they are not underwater. To hear sounds underwater, they make use of their lower jawbone, that conducts sounds to their middle ear.
Dolphins use echolocation underwater, much just like whales. Echolocation allows dolphins to locate objects underwater by transmitting sound waves. They generate a high-pitched sound pulse or clicks in their foreheads that send sound signals into the water. The echo produced by the sound bouncing off objects helps the dolphins in locating the objects, even determining how far away the objects are located. The dolphins sense the returning sound vibration by feeling the pulses on their jaws. Each object or animal underwater sends off different echoes, which the dolphins can differentiate.
Echolocation helps dolphins determine not only the distance of an object but also the texture, shape and size of the object. It works because water is an excellent sound transmitter, which can transmit sound five times faster compared to air.
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SONAR (SOund Navigation And Ranging) is the method that dolphins and whales use in navigating under murky waters. As explained in echolocation, they use the sound transmissions that echo back to locate things. Even when it is dark underwater, they can still find food and avoid dangerous places. Dolphins produce two kinds of sounds, the high-pitched whistling sound and the rattle or clicking sound. The whistles act as communicators while the rattles or clicks act as the SONAR.
To better understand the quality of the dolphin's sense of hearing, we shall compare it with humans, dogs and whales. Dolphins have sharper hearing senses than humans do; they can hear a broader range of frequencies. Humans hear sounds from 20 Hz to 20 KHz while dolphins hear from 20Hz to 150 KHz. This means dolphins can hear seven times better than humans do.
When comparing dogs to humans, dogs hear far better than human beings do. Dogs are able to hear high frequencies humans cannot hear, about two times better. However, the dolphin has a hearing range that far exceeds than that of dogs, about five times better. Of all mammals, dolphins are able to hear and produce some of the highest frequency sounds.
Dolphins when compared to whales, usually communicate using high frequencies while whales often use low frequencies. The whales can communicate at farther distances (several hundred or kilometers away) than dolphins can.