2 minute read


Marine Mammals

Echolocation may work better under water than it does on land because water is a more effective and efficient conveyer of sound waves. Echolocation may be more effective for detecting objects underwater than light-based vision is on land. Sound with a broad frequency range has a more complex interaction with the objects that reflect it than does light. For this reason, sound can convey more information than light.

Like bats, marine mammals such as whales, porpoises, and dolphins emit pulses of sounds and listen for the echo. Also like bats, these sea mammals use sounds of many frequencies and a highly direction-sensitive sense of hearing to navigate and feed. Echolocation provides all of these mammals with a highly detailed, three-dimensional image of their environment.

Whales, dolphins, and porpoises all have a weak sense of vision and of smell, and all use echolocation in a similar way. They first emit a frequency-modulated sound pulse. A large fatty deposit, sometimes called a melon, found in its head helps the mammal to focus the sound. The echoes are received at a part of the lower jaw sometimes called the acoustic window. The echo's vibration is then transmitted through a fatty organ in the middle ear where it is converted to neural impulses and delivered to the brain. The brains of these sea mammals are at least as large relative to their body size as is a human brain relative to the size of the human body.

Captive porpoises have shown that they can locate tiny objects and thin wires and distinguish between objects made of different metals and of different sizes. This is because an object's material, structure, and texture all affect the nature of the echo returning to the porpoise.

Like bats, the toothed whales have specially adapted structures in the head for using echolocation. Some species of toothed whales have a bony structure in the head that insulates the back of the skull where sounds are received from the front of the skull where sounds are produced. The middle ear cavity is divided into a complex sinus that may help to acoustically separate the right and the left ears. This would enable the whale to more easily glean information from the echoes it receives. Other structures help to reduce the confusion of transmitted and received sound throughout the skull.

See also Acoustics; Cetaceans; Radar.



Campbell, N., J. Reece, and L. Mitchell. Biology. 5th ed. Menlo Park: Benjamin Cummings, Inc. 2000.

Harrison, Richard, and M. M. Bryden, eds. Whales, Dolphins, and Porpoises. New York: Facts on File, 1988.

John Henry Dreyfuss


. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


—For a sound wave, the number of waves that pass a given point per unit of time.


—A unit of measurement for frequency, abbreviated Hz. One hertz is one cycle per second.


—Any animal that feeds on insects.

Ultrasonic vibrations

—Acoustic vibrations with frequencies higher than the human threshold of hearing.

Additional topics

Science EncyclopediaScience & Philosophy: Dysprosium to Electrophoresis - Electrophoretic TheoryEcholocation - Bats, Marine Mammals