Supplementary material from "Hearing and anatomy of the ear of the European hedgehog Erinaceus europaeus"

A major threat to the declining European hedgehog (Erinaceus europaeus), is road traffic. Devising methods to reduce the number of collisions would increase hedgehog welfare in an urbanised world, and serve to protect this flagship species, and this goal might be advanced by an understanding of their hearing. This study investigates the auditory capabilities and anatomy of the ear of the European hedgehog. Using auditory brainstem response (ABR) testing on 20 live hedgehogs from Danish wildlife rescue centres, we measured hearing thresholds across 4-85 kHz, and found a peak sensitivity around 40 kHz, revealing that European hedgehogs can hear sound frequencies of at least 4-85 kHz. Complementary post mortem micro-CT scans enabled a detailed 3D reconstruction of the inner ear, revealing small middle ear bones with a cochlear spiral of approximately 1.7 turns. Results show that hedgehogs can perceive a broad ultrasonic range, which provides important cues for directional hearing and may additionally function in prey detection and communication. These findings provide critical insights into hedgehog sensory biology and inform the potential development of ultrasonic repellents to mitigate traffic collisions and habitat disturbances, contributing to conservation strategies for this declining species.