Natural sounds and national parks: a synthesis examining benefits to human health

To examine the distribution of natural sounds in national parks, we used the National Park Service Natural Sounds and Night Skies Division (NSNSD) nationwide acoustic dataset. Detailed methods of acoustic recording collection and analysis are outlined in Lynch, Joyce and Fristrup (2011) and Buxton, et al. (2019). Briefly, the NSNSD has been monitoring the acoustic environment since 2000. Trained technicians identified sounds to categories (anthropogenic, geophysical, and biological) by listening to and observing spectrograms of subsampled recordings at 221 sites in 68 parks (SI Appendix,Table S3). Broad anthropogenic noise categories included aircraft, motorized vehicles, people talking, domestic animals, trains, and infrastructure maintenance (e.g., grounds-care); geophysical sounds included wind, water, geothermal activity, and thunder; and biological sounds included those from insects, mammals, amphibians, and birds. These sound types were identified as present or absent in 10-second samples of audio taken continuously, or every 2 or 5 mins (SI Appendix,Table S3). We calculated the audibility of sounds as the proportion of 10-second acoustic samples where a sound was observed during an hour of sampling.