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How does the Doppler effect help some bats measure the speed of their prey?

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bat Livingstone's fruit bat (*Pteropus livingstonii*) in flight.

Some bats use the Doppler effect to measure the velocity of their prey during echolocation.

Specifically, bats that utilize constant frequency (CF) pulses can detect a shift in the frequency of the returning echo caused by the relative motion between the bat and its target. By analyzing this change in perceived frequency, the bat is able to calculate the velocity of the prey it is tracking.1