Mechanism

Echolocation as used by the odontocetes is manifested as a series of clicks with variations on this theme made by various species. Sperm whales, for instance, may emit individual clicks separated by a matter of seconds or tenths of seconds, whereas bottlenose dolphins may emit click trains with a frequency at or above 600 clicks per second. A click train with a frequency over 600 clicks per second is called a burst pulse. The whaled produce the individual clicks by passing air from an air sack called the bony nares, which is forward of the trachea and behind the mouth, through various air passaged constricted and controlled by the dorsal bursae and finally through the phonic lips. The sounds emitted in this fashion are focused by the melon, a sack that rests above the jaw. Inside the melon are lipids of various densities which act as a sort of phonic lens, allowing the whale to focus the sound according to the frequency of the burst pulse, the depth at which it is operating and the range at which it wishes to detect objects and prey.

Odontocetes receive their auditory signals through the lower jaw, which is hollow, allowing the sounds to reverberate and easily transmit to the ear. From the rear end of the jaw, sounds are transmitted to the inner ear through a dedicated continuous lipid body. Sound can also be received laterally through fatty lobes that surround the ear called the auditory bullae. These bodies have a similar density to bone, optimizing reception at similar frequencies to the jaw. The brain of toothed whales can interpret directionality of the echo of the sound they transmit by direction using the directionality of the organs receiving the sounds. Bottlenose dolphins can interpret individual clicks at up to around 600 clicks per second, whereas at frequencies higher than that, they are interpreted less efficiently.