Redefining doppler shift compensation: Noise suppression for prey detection in bats

Echolocating bats employ Doppler shift compensation (DSC) to stabilize echo frequencies during flight, traditionally thought to enhance auditory sensitivity by aligning echoes with the acoustic fovea. However, a puzzling contradiction has emerged: bats do not compensate for echoes from the moving prey they are actively targeting. To investigate this paradox, we examined the acoustic criteria underlying DSC in Japanese horseshoe bats (Rhinolophus nippon) using real-time playback and free-flight experiments. We found that bats consistently compensated for echoes with the highest frequencies, regardless of their intensity. This selectivity generated a “quiet frequency band” just above the reference frequency, effectively excluding background clutter. While prior studies have mostly focused on DSC during passive flight, few have explored its role in active prey capture. To address this gap, we conducted controlled prey-capture experiments and found that bats received frequency glints—spectral modulations arising from fluttering prey—within the quiet band. Playback of noise within this band significantly reduced attack rates. These findings suggest that DSC is not merely for shifting echoes into the sensitive range but for excluding interfering echoes from it—thus enhancing signal-to-noise ratio for prey cues. Our study redefines the function of DSC as a strategy for auditory scene optimization under acoustically complex conditions.