<b>Urban Birds Fall into A Communication Trap Through Mismatched Vocal Compensation and Auditory Function</b>

Here, we show that urban environments are associated with a mismatch between signal production and reception. In a common urban bird, the Eurasian tree sparrow (<i>Passer montanus</i>), urban and rural populations differ markedly in syllable repertoires, with only a subset of syllable types shared between habitats.

Acoustic differences therefore reflect both changes in syllable composition and syllable-specific modifications of shared syllables, including higher peak frequencies and intensities in several urban syllable types. In parallel, urban birds exhibit selective reductions in auditory responsiveness, smaller ear apertures, and degraded cochlear hair cells, indicating constrained peripheral input. At the neural level, urban individuals show reduced neurogenesis in both the lateral ventricle and <a href="" target="_blank">caudomedial </a>nidopallium, alongside proteomic shifts toward stress responses and synaptic maintenance and away from neuronal development.