Bats create a silent frequency band to detect prey through Doppler shift compensation

Acquiring information efficiently through sensory inputs is essential for animal survival. Animals with active sensory systems that emit their own signals often optimize the design and use of these signals according to context and purpose1-6. In this study, we reveal a previously unrecognized function of Doppler shift compensation (DSC) in bats. During flight, bats actively lower the frequency of their echolocation calls so that echoes remain stable at a reference frequency (fref) despite Doppler shifts caused by movement7-12. We demonstrate that DSC does not simply serve, as previously thought, to align echoes with the acoustic fovea--a narrow band of maximal auditory sensitivity13,14--but in addition, suppresses background noise for detecting prey-derived signals. Using phantom echo playbacks and on-board microphone recordings, we show that bats selectively compensate for the highest-frequency echoes rather than the most intense ones. This process shifts all clutter echoes below fref, leaving the spectral band above fref free of stationary-object echoes and secures a "quiet frequency band". Recordings during prey capture and noise playback experiments revealed that spectral glints from fluttering moth wings appear in this "quiet frequency band" and are exploited for prey detection. This mechanism enhances the high-fidelity detection of prey echoes even in cluttered environments. Such findings reveal a sensory strategy in which animals actively create silence in a critical frequency range. It represents a conceptual advance in active sensing and auditory scene analysis, highlighting how evolution shapes sensory systems to extract reliable information under noisy natural conditions.