Can you hear me? House sparrow auditory processing differs across an urbanization gradient.

Urbanization alters both the physical and sensory environments of habitats and has the potential to affect animal communication. While the challenges faced by signalers in urban environments are increasingly understood, far less is known about how urbanization influences the physiology or behavior of sensory receivers. Here, we examined the relationship between urbanization and auditory sensitivity of house sparrows (Passer domesticus), a human-commensal songbird that inhabits environments spanning a rural–urban gradient. We used auditory brainstem responses (ABRs) to assess hearing sensitivity across individuals captured at sites differing in urbanization. We predicted that urban-living would be associated with frequency-dependent changes in auditory sensitivity. In particular, we expected that urban sparrows may have greater high-frequency sensitivity compared to their rural counterparts, consistent with reported shifts in urban song structure. Overall, our results showed mixed support for this prediction. Increased levels of urbanization were associated with lower hearing sensitivity and greater delays in the ABR but the exact magnitude and direction of these effects depended on how urbanization was quantified, the sex of the individual, and the features of the acoustic stimulus. These changes in auditory processing with urbanization may reflect a communication cost to sensory receivers or, alternatively, a mechanism for avoiding noise masking. These findings are some of the first evidence in songbirds that the sensory physiology of receivers, not just signalers, can be impacted by human activity.