In echolocating bats, auditory sensitivity and processing are crucial adaptations, enabling precise navigation, prey detection, and environmental perception in low-light or completely dark conditions (Kick and Simmons, 1984; Neuweiler, 2000). Unlike visual or olfactory senses, echolocation provides bats with the ability to construct detailed spatial images by emitting high-frequency calls and analyzing returning echoes to discern object distance, size, shape, and movement (Moss and Surlykke, 2001). This auditory adaptation is particularly vital for insectivorous and nocturnal species that depend on accurately locating and capturing small, agile prey (Moss and Schnitzler, 1995; Schnitzler and Kalko, 2001). Advanced auditory functions have driven bats to develop highly specialized neural pathways that process echoes with exceptional accuracy and speed, supporting their ecological roles as nocturnal hunters and navigators (Beetz and Hechavarría, 2022; Corcoran and Moss, 2017).

Studies in bat neurophysiology indicate that their auditory systems are finely tuned to each species’ specific foraging and habitat needs. For instance, frequency-modulating (FM) bats, which produce short, broadband signals, rely on rapid temporal resolution to detect and track fast-moving prey in cluttered environments (Moss and Surlykke, 2001; Schnitzler and Kalko, 2001). In contrast, constant frequency (CF) bats optimize their calls for long-duration, narrowband signals, allowing them to detect fluttering insects amid dense foliage through Doppler-shifted echoes (Hiryu et al., 2016; Smotherman and Guillén-Servent, 2008). These adaptations underscore the diversity of bat echolocation strategies, with each species modifying auditory mechanisms to enhance survival in distinct ecological niches (Grothe, 2000; Neuweiler, 2000; Pollak and Casseday, 2012). Neurophysiological studies further show that delay-tuned neurons in bat midbrains respond selectively to specific pulse-echo delays, aligning the neural response to the typical detection distances at which bats encounter and capture prey (Beetz and Hechavarría, 2022; Feng et al., 1978; O'Neill and Suga, 1979; Valentine and Moss, 1997).

The auditory brainstem response (ABR) method provides a fast, minimally invasive approach to measuring auditory thresholds, making it a standard for audiometry in humans and widely applicable in vertebrates (Burkard et al., 2007; Corwin et al., 1982; Eggermont, 2019). In recent years, the application of ABRs in bats has gradually emerged, such as in Pipistrellus abramus (Boku et al., 2015; Simmons et al., 2015), Eptesicus fuscus (Simmons et al., 2022), Miniopterus fuliginosus (Furuyama et al., 2018), Phyllostomus discolor (Linnenschmidt and Wiegrebe, 2019), and Carollia perspicillata (Wetekam et al., 2020); these studies revealed that auditory thresholds closely align with echolocation frequencies, supporting prey detection and navigational precision essential for foraging efficiency and obstacle avoidance.

The great evening bat (I. io), one of the largest members of Vespertilionidae, is unique among bats for its predation on birds in southern China and northeastern India (Gong et al., 2021, 2022; Thabah et al., 2007). As an FM bat, I. io produces echolocation calls with 3 to 4 harmonics, with the peak frequency centered around 29 kHz in the first harmonic (Feng et al., 2001). Compared to most other FM bats, the lower echolocation call peak frequency of I. io facilitates their detection and predation of large prey, including large moths and bird prey (Gong et al., 2023, 2024). In this study, we used ABR to assess the auditory thresholds of I. io across a 2 to 80 kHz range, and further link sensitivity to ecological adaptations and echolocation patterns. Through this study, we aim to advance the understanding of auditory processing in I. io and contribute to broader knowledge on the relationship between echolocation frequency and auditory sensitivity in bats, adapted to the unique demands of different environmental contexts.