Spatial distribution of acoustic traits in bird assemblages along regional bioclimatic gradients

Environmental variation shapes acoustic interactions among birds, creating spatial structures in the sonic signature of local species assemblages. Exploring these patterns at regional scales can reveal processes that segregate acoustic strategies along environmental gradients. Here, we examined how the acoustic trait composition of bird assemblages varies at a regional extent in relation to landscape resolution environmental variation. We used data on 2427 bird assemblages and 15 acoustic traits, quantifying the frequency, complexity, rhythm, and duration of vocalisations for 117 species. We used multivariate ordinations to investigate the distribution of species' acoustic traits along climatic and landscape gradients while accounting for spatial and phylogenetic dependencies. We then assessed whether these relationships resulted in directional shifts in the acoustic trait composition of bird assemblages for three key acoustic traits. Our results show that acoustic traits were phylogenetically and spatially clustered and correlated with regional climatic conditions (e.g. lower complexity and isochronous rhythms under higher precipitation and temperature seasonality). Conversely, we found mixed support for the hypothesis that the acoustic signature of species assemblages is shaped by habitat composition within landscapes. For instance, we found urbanisation to be associated with vocalisations featuring broader spectral bandwidths, likely facilitating their propagation under noise pollution, but also greater complexity, which may hinder transmission in urban landscapes. These regional patterns may reflect differences in the structure of acoustic networks within and among species assemblages. Our results thus form a first step towards a regional‐level assessment of the environmental and anthropogenic factors that structure or disrupt acoustic connectivity in landscapes.