Echolocation, also called biosonar, is the biological sonar used by several animals such as dolphins, shrews, most bats and whales. It is important to marine mammals because it allows them to navigate and feed in the dark at night and in deep or murky water where it isn’t easy to see.
Toothed whales emit a focused beam of high-frequency clicks. Sounds are generated by passing air from the bony nares through the phonic lips. These sounds are reflected by the dense concave bone of the cranium and an air sac at its base. The focused beam is modulated by a large fatty organ known as the ‘melon’. This acts like an acoustic lens because it is composed of lipids of differing densities. Most toothed whales use clicks in series, or click train, for echolocation. Toothed whale whistles do not appear to be used in echolocation. Different rates of click production in a click train result on familiar barks, squeals and growls of the bottlenose dolphin.
The major areas of sound reception are the fat-filled cavities of the lower jaw bones. Sounds are received and conducted through the lower jaw to the middle ear, inner ear, and then to hearing centers in the brain via the auditory nerve. Lateral sound may be received through fatty lobes surrounding the ears with a similar acoustic density to the bone. The brain receives the sound waves in the form of nerve impulses, which relay the messages of sound and enable the dolphin to interpret the sound’s meaning.
Bottlenose dolphins are able to learn and later recognize the echo signatures returned by preferred prey species.