echolocation

Method used by certain animals, notably bats, whales, and dolphins, to detect the positions of objects by using sound. The animal emits a stream of high-pitched sounds, generally at ultrasonic frequencies (beyond the range of human hearing), and listens for the returning echoes reflected off objects to determine their exact location.

The location of an object can be established by the time difference between the emitted sound and its differential return as an echo to the two ears. Echolocation is of particular value under conditions when normal vision is poor (at night in the case of bats, in murky water for dolphins). A few species of bird can also echolocate, including cave-dwelling birds such as some species of swiftlets and the South American oil bird.

The frequency range of bats' echolocation calls is 20–215 kHz. Many species produce a specific and identifiable pattern of sound. Bats vary in the way they use echolocation: some emit pure sounds lasting up to 150 milliseconds, while others use a series of shorter ‘chirps’. Sounds may be emitted through the mouth or nostrils depending on species.

Blind or blindfolded human subjects can also learn echolocation to a certain degree. People who have used it from an early age are particularly successful with the technique, using tongue-clicking, tapping with a stick, or stamping sounds to create the required echoes.

Echolocation was first described in the 1930s, though it was postulated by Italian biologist Lazzaro Spallanzani (1729–1799).