Auditory sensitivity in the great evening bat (Ia io): Insights from auditory brainstem response

The great evening bat (Ia io), a large frequency-modulating (FM) bat species in the Vespertilionidae family, may exhibit unique auditory adaptations that support its bird-predatory behavior. In this study, we employed auditory brainstem response (ABR) measurements to evaluate the auditory sensitivity of five adult male I. io across a 2 to 80 kHz frequency range. The results showed the most sensitive auditory threshold appears at 24-28 kHz (range 24 to 32 kHz for individual bats), aligning with the species' peak frequency of echolocation calls, enhancing large prey detection and localization. ABRs identify five distinct wave peaks (P1-P5) at high sound pressure levels, with the largest amplitude peak observed for P4. Furthermore, I. io has lower auditory thresholds across higher frequencies than most other FM bats. These findings suggest I. io has a broad auditory range that may facilitate adaptive flexibility in varied ecological settings.