Vocal amplitude control of resting bats tracking approaching tethered insects by echolocation in both silence and noise conditions. (Top) High-speed video filming the behavior of the bat. (Middle) The waveform of the echolocation calls showing the peak amplitude. (Bottom) The spectrogram of the echolocation calls. High-speed video was recorded at a frame rate of 250 Hz, and the calls were recorded at a sampling rate of 250 kHz. Here, both video and sound recordings were slowed down by a factor of 5.2 to make the ultrasonic calls audible to human ears.