Acoustic Space is Affected by Anthropogenic Habitat Features: Implications for Avian Vocal Communication

Human-altered landscapes often include structural features, such as higher levels of impervious surface cover (ISC) and less vegetation, that are likely to affect the transmission of avian vocalizations. We investigated the relationships between human habitat modifications and signal transmission by measuring four acoustic parameters—persistence, reverberation, and signal-to-noise ratio (SNR) of broadcast tones, as well as absolute ambient noise level—in each of 39 avian breeding territories across an anthropogenic disturbance gradient. Using a geographic information system, we quantified the amounts of different habitat features (e.g., ISC, grass, trees) at each site; a principal component analysis was used to identify which of these habitat features commonly co-occurred (e.g., “habitat suites”). Finally, we used a model selection process to explore whether the habitat suites predicted the acoustic parameters. Tone persistence was higher and reverberation was lower in more open, grassy habitats than in areas with more vertical anthropogenic structures. In more human-modified sites, ambient noise levels were higher, leading to lower SNR. In habitats with low levels of human modification, we found that even small increases in the total amount of open—grassy area will quickly improve the acoustic space of singing birds. However, our results also indicated that there may be a critical level of human habitat modification above which the addition of “natural” areas does not benefit avian communication. Thus, we recommend that managers focus their efforts on preserving pre-existing “natural” habitat, rather than attempting to introduce it into areas that have already received significant human modification