Saturday, May 17, 2008

Echolocation

Echolocation is the use of the echoes of sounds produced by certain animals to detect obstacles in their path and perhaps to locate food. The term echolocation was coined (1944) by Donald R. Griffin to describe this process. The list of echolocators includes may bats, porpoises, some whales, several species of birds and some shrews. Blind people and animals that live where the lighting is unpredictable also use a form of echolocator.

Sound used in echolocation may be produced in the voice box, the mouth, or some part of the head, and in all cases highly refined auditory systems detect returning echoes. For echolocation to work, each outgoing pulse of sound must be registered in the organism's brain, where it will be compared to its echo. Porpoises, birds, and some bats use loud orientation sounds, which pose a problem of self-deafening. The problem is resolved in bats by neutral and muscular modifications in their auditory system.

Echolocation is mistakenly associated with high-frequency sound, or ultrasound. In fact, the echolocations sounds of oil birds and cave shiftiest are quite audible to the human ear, as are those of some bats. Most bats use pulses of ultrasonic sound (inaudible to humans) because high-frequency sounds provide better resolution of targets than do lower-frequency sounds. Insectivorous bats use a wide array of echolocation strategies involving changes in loudness and frequency.

A bat judges the distance to its prey by reflecting sounds it has emitted. Echolocation is also used to navigate in dark caves or at night.

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