A synthesis of health benefits of natural sounds and their distribution in national parks

Abstract

Parks are important places to listen to natural sounds and avoid human-related noise, an increasingly rare combination. We first explore whether and to what degree natural sounds influence health outcomes using a systematic literature review and meta-analysis. We identified 36 publications examining the health benefits of natural sound. Meta-analyses of 18 of these publications revealed aggregate evidence for decreased stress and annoyance (g = -0.60, 95% CI = -0.97, -0.23) and improved health and positive affective outcomes (g = 1.63, 95% CI = 0.09, 3.16). Examples of beneficial outcomes include decreased pain, lower stress, improved mood, and enhanced cognitive performance. Given this evidence, and to facilitate incorporating public health in US national park soundscape management, we then examined the distribution of natural sounds in relation to anthropogenic sound at 221 sites across 68 parks. National park soundscapes with little anthropogenic sound and abundant natural sounds occurred at 11.3% of the sites. Parks with high visitation and urban park sites had more anthropogenic sound, yet natural sounds associated with health benefits also were frequent. These included animal sounds (audible for a mean of 59.3% of the time, SD: 23.8) and sounds from wind and water (mean: 19.2%, SD: 14.8). Urban and other parks that are extensively visited offer important opportunities to experience natural sounds and are significant targets for soundscape conservation to bolster health for visitors. Our results assert that natural sounds provide important ecosystem services, and parks can bolster public health by highlighting and conserving natural soundscapes.

Keywords: bird song; noise; stress; visitor experience; water sounds.

Fig. 1.

Health and positive affective outcomes improved while stress and annoyance decreased in studies examining the benefits of exposure to natural sounds. Weighted mean effect sizes are from meta-analytic models of 18 studies, and the error bars indicate 95% CIs. A positive mean value (to the right of the dashed zero line) indicates health and positive affective outcomes improved in groups exposed to natural sound, and a negative value (to the left of the dashed zero line) indicates stress and annoyance indicators decreased in groups exposed to natural sound. Examples of metrics of health and positive affect included improved mood and cognitive ability, and metrics of stress and annoyance included decreased pain, heart rate, and blood pressure. All images are free for use, no attribution required.

Fig. 2.

Weighted mean effect sizes of natural sound on health and positive affective outcomes and stress and annoyance outcomes for different types of natural sounds and different treatment comparisons. Water sounds had the largest mean effect size for health and positive affective outcomes, bird sounds had the largest for stress and annoyance, and comparing natural sound to noise had the largest for health and positive affect and stress and annoyance. The error bars indicate 95% CIs. A positive mean value (to the right of the dashed zero line) indicates health and positive affective outcomes improved in groups exposed to natural sound, and a negative value (to the left of the dashed zero line) indicates stress and annoyance indicators decreased in groups exposed to natural sound. Part of the x-axis is removed for display purposes.

Fig. 3.

The proportion of each type of sound (biological—sounds produced by animals; geophysical—sounds from water, wind, and weather; and anthropogenic—sounds produced by humans) observed in recordings collected in parks across the United States indicate acoustic environments important for human health—sites where natural sounds are more abundant (darker colors—higher audibility) and anthropogenic sounds are less abundant (larger circles—lower audibility). Audibility of sounds are predicted by generalized linear mixed models. Note that sites were not selected at random within parks or regions; they were selected to monitor specific settings of interest to park managers.

Fig. 4.

Many US park sites near urban areas had a high proportion of recordings containing biological (Top—produced by animals) and geophysical (Lower—from water, wind, and weather) sounds but also high anthropogenic sounds (smaller points). Sites within urban areas (red) with high audibility of biological and geophysical sound could represent important acoustic environments important for the health of urban visitors. Audibility is the proportion of each type of sound observed in subsampled recordings collected in parks across the United States predicted by generalized linear mixed models.