HEALTH
In 2019, conservation biologist Rachel Buxton teamed up with researchers from the US National Park Service (USNPS) and Colorado State University to study how noise pollution in America’s national parks affects people and animals. Noise can cause humans to suffer stress, high blood pressure and other ailments. It also makes it harder for animals to find food and mates. In fact, Buxton refers to one study that measured how various factors such as loss of sleep and illness due to noise pollution resulted in the loss of “healthy life years” (years of life in a healthy state). It estimated that loss at 650,000 years — ten times more than cardiovascular disease. As she studied the negative consequences of noise, Buxton began to wonder whether natural sounds would have a positive effect.
To find out, Buxton — who’s a professor at Carleton University in Ottawa, Canada — and colleagues from six universities and the USNPS reviewed three dozen past studies exploring the measurable health benefits of natural sound. The review covered more than a decade’s worth of studies, conducted all around the world, with a wide range of methods. Some researchers had measured blood pressure, heart rate and the stress hormone cortisol, others had studied reactions to sound such as feelings of annoyance or tranquility, awareness, relaxation and cognitive function. Among the findings: those who were exposed to natural sound saw a whopping 184 percent improvement in their overall health, including lower blood pressure, improved cognitive performance and even reduced pain.
Other studies were also compelling. A Swedish group, for instance, found that humans in virtual nature environments — complete with sounds — recovered better from stress than those in the same surroundings without sound. A team of Iranian scientists found that ICU patients on ventilators reported less pain when they listened to natural sounds via headphones. Overall, the meta-analysis found an average 28% reduction in feelings of annoyance when listening to natural sounds such as birds, wind, and water. Those traditional markers of health — such as blood pressure, heart rate, and perceived pain — were all reduced (23%) by the sound of water running over rocks and the like.
Many of the studies used similar natural sounds, especially pleasant birdsong and the sound of water. A statistical analysis found the sound of birds proved best at alleviating stress and annoyance. The sound of water, on the other hand, boosted both overall health and emotions such as tranquility.
Even a mix of natural and human-made sounds can be beneficial. In several studies, scientists mixed the sound of running water or singing birds with unwanted noise, such as traffic. They found people often reported feeling less annoyed and more tranquil. But scientists don’t know whether natural sounds actually help mask unwanted noise to the ear, or if people are simply able to enjoy them even when the sounds are paired with less desirable noise.
As part of her work, Buxton measured the prevalence of sound in US National Parks, in part to help inform park administrators — especially those in heavily visited parks — how to organise infrastructure to preserve areas of rich soundscape. From 221 audio recordings from 68 National Park sites, 75% of them were found to have high levels of natural sounds 75% of the time.
“In parks, noise degrades visitor enjoyment and health directly as an environmental stressor and indirectly by altering the number of sound-producing animals and thus decreasing the diversity of natural sounds,” she wrote. However, when natural sounds were audible in combination with human-made noise, the negative effects of noise pollution were largely reduced.
Sounds cause reactions in every known vertebrate, and most animals and even plant life have evolved to perceive sound as an important way of navigating the environment, finding food and mates, and avoiding danger. So, obscuring sounds by noise pollution can cause detrimental neurological effects, such as an increase in cortisol secretion that can lead to a loss of wellness.
One prevailing theory as to why natural soundscapes promote healing is that they usually don’t require our attention, and can allow us to “switch off” our auditory focus, something we can almost never do in the constant stimulation of an urban environment.
Though the sounds were natural, much of the work Buxton studied was done in a lab or a hospital. So more study will be needed to explore how sounds may affect people when heard in their natural environment. And most of the research explores reactions to just a few common sounds such as running water and pleasant birdsong. “Maybe a seagull cawing at 6am might produce a different reaction,” Buxton jests.
Seeking out the sounds of nature may be quite a change for humans more accustomed to tuning out the annoying din of noisy cities and suburbs. But Buxton is convinced such efforts will be rewarded. “For me these sounds are treasures," she told the Smithsonian. “They’re amazing natural resources, and how remarkable that they are also really good for our health and our wellbeing.”