Bats 'see' with sound pulses pitched above human hearing

Bats emit rapid ultrasonic calls and read the returning echoes to build a moving map of insects and obstacles in total darkness, pulsing over 20 times a second as they close in on prey. Lazzaro Spallanzani showed in the 1790s that blinded bats still navigated fine but earless ones couldn't; it took until 1938 for Donald Griffin and Robert Galambos to identify the mechanism as biological sonar.

— Donald R. Griffin, Listening in the Dark: The Acoustic Orientation of Bats and Men — Yale University Press, 1958
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