Non-invasive auditory brainstem response measurements in an unanesthetized Humboldt penguin ( <i>Spheniscus humboldti</i> )

Hearing thresholds are vital for assessing anthropogenic noise impacts on animals, yet commonly used electrophysiological techniques can pose welfare concerns from invasive electrodes and required anesthesia. This study investigated if auditory brainstem responses (ABRs) were measurable via surface electrodes from an unanesthetized Humboldt penguin (Spheniscus humboldti). Successful ABR recordings generated thresholds between 36 and 41 dB re 20 μPa rms to click stimuli centered at 2 kHz, similar to previous data from penguins and other diving birds. This provides proof-of-concept that non-invasive electrophysiological techniques are achievable for penguins and potentially other species of conservation and welfare concern.