Relative effects of ambient noise and habitat openness on signal transfer for chickadee vocalizations in rural and urban green-spaces

Urbanization creates communication challenges for many species. Birds in particular rely on vocal communication for reproduction and territory defence, but in noisy or acoustically altered environments signals may be compromised. Both ambient noise and habitat openness affect signal transfer, but it is not clear how these two variables interact in urban green-spaces. Using black-capped and mountain chickadee vocalizations, we conducted transmission experiments to measure acoustic degradation and signal-to-noise ratios among a replicated set of transects spanning a range of both ambient noise levels and habitat openness. We used Akaike information criterion (AIC), an information theoretic approach, for selection and averaging of five alternative linear mixed models. We found ambient noise strongly and negatively correlated with relative signal amplitude and detection of signal features. In contrast, habitat openness appeared to have little effect on signal transfer. We also confirmed that urban green-spaces had significantly greater ambient noise levels than rural sites, which suggests that the dominant impact of anthropogenic noise on signal transfer should be an issue of concern to species conservation within these urban green-spaces.