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Bats have an adjustable sonar

india Updated: Dec 29, 2006 15:51 IST
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Bats are quite skillful users of sonar, producing acoustic pulses and analysing the echoes to locate prey and other objects.

More evidence of their skill is revealed in a study by Erin H Gillam of the University of Tennessee and colleagues, who show that bats can rapidly shift the frequency of their acoustic pulses to avoid interference from the signals of other bats or from ambient noise in the environment.

Such ‘jamming avoidance’ would be necessary to avoid the confusion created when a bat receives many different echoes at the same frequency and cannot determine which are its own.

While earlier studies had strongly implied that jamming avoidance occurs, direct experimental evidence of it had been lacking. In the new study — published in Proceedings of the Royal Society B — the researchers exposed Brazilian free-tailed bats to recorded echolocation calls at one of six frequencies.

No matter what frequency was used, the bats responded by shifting the frequency of their own calls away from it – presumably so that the echoes from their calls would remain distinct and recognisable.

In another experiment, the researchers abruptly shifted the frequency of the recorded calls as bats approached the source of the sound. The bats responded immediately, by increasing the frequency of their own calls.

Even if their initial call frequency was lower than that of the recorded one, they responded by increasing theirs to a higher frequency, in effect jumping over the recorded frequency. And they made the shift in about one-fifth of a second.

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