Miles away from the nearest road in Colorado’s Wheeler Geologic Area, the problem of noise pollution hit home for conservation biologist Rachel Buxton. ‘It was a gorgeous, remote valley, and then a plane flew over and you could hear the noise for ages as it reverberated in the valley,” she says. “I remember thinking, ‘wow, this is a really pervasive issue.’”
Buxton teamed up with researchers from the National Park Service and Colorado State University to author a 2019 study documenting manmade noise in U.S. national parks. The study was part of a growing pile of research exploring noise’s negative impacts on animals and humans alike. Noise makes it hard for animals to find food and mates and can lead humans to suffer stress, high blood pressure and other ailments.
But as she studied the negative consequences of noise, Buxton also began considering the opposite scenario: could the natural sounds with which she’d always been enamored, have positive consequences? “If I’m hearing lots of pleasant natural sounds, or many birds singing, is that better than hearing nothing?” she wondered.
To find out, Buxton and colleagues from six universities and the National Park Service did a statistical analysis of some three dozen past studies exploring the measurable health benefits of natural sound. Though the goals and methods of the analyzed studies varied widely, some common themes emerged—the various groups exposed to natural sound saw a 184 percent improvement in overall health outcomes. Buxton’s research, published in March in Proceedings of the National Academy of Sciences, presents evidence that pleasant natural sounds can help lower blood pressure, improve cognitive performance and even reduce pain. “Typical natural sounds that we consider pleasant are having health benefits for us,” says Buxton, a professor at Carleton University in Ottawa, Canada. “I think that’s a really powerful message,”
To explore the possible health benefits of natural sound, the team analyzed more than a decade’s worth of studies, conducted around the world, with a wide range of methods. Some researchers had measured outcomes linked to human health like blood pressure, heart rate and the stress hormone cortisol. Other scientists had studied reactions to sound that may impact health for good or ill—including feelings of annoyance or tranquility, awareness, relaxation and cognitive function.
Each study investigated the impacts that certain natural sounds had on subjects, and the intriguing results varied widely. 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.
Many of the studies had used similar natural sounds, especially pleasant birdsongs and the sounds of water. Buxton’s team conducted a statistical analysis that synthesized results and found that the bird sounds proved best at alleviating stress and annoyance. Water sounds, on the other hand, boosted both overall health outcomes and positive emotions like tranquility.
Bryan Pijanowski, who directs Purdue University’s Center for Global Soundscapes and wasn’t involved in the research, says that most of the work in the past has been on some of the harmful impacts of urban noise pollution. “So they’ve kind of turned this around and said natural sounds have this positive effect. There aren’t a lot of studies on it, so they’ve done an exceptional job of pulling this together and showing how sound has a positive effect on you in the psychological sense, and in the physiological sense.”
Though the sounds were natural, much of the work Buxton studied was done in lab or hospital settings. More study is needed to explore how sounds may actually impact humans when heard in their natural environment. And most of the existing research explores reactions to just a few common sounds like running water and the pleasant songs of different birds. “Maybe a seagull cawing at 6:00 a.m. might produce a different reaction,” Buxton says.
In a second part of their study, Buxton and colleagues explored soundscapes throughout the U.S. national parks to find out where such beneficial sounds might be enjoyed. Pinpointing sites where listeners enjoy lots of natural sound and less noise, even in busier parks, can help managers protect and enhance the soundscapes so important to tourists’ park visitation experiences and, as it turns out, possibly helpful to their health. The National Park Service proved an ideal partner at this aspect, because its experts are already attuned to listening for exactly what kind of sounds park visitors hear.
In recent years the NPS Natural Sounds Program has monitored over 892 unique sites in 123 different park sites throughout their system. They record and analyze all the sounds that humans hear in in these special places to help mitigate unwanted noise and help scientists understand how natural sounds benefit health. (Visitors can experience some of those soundscapes, like the two embedded in this article, in the Sound Gallery curated by the NPS and Colorado State University.)
Tapping into these extensive audio resources the study authors analyzed recordings from some 221 sites in 68 different national park sites. Colorado State University students trained as technicians combed through them to identify the origins, frequency and volume levels of all the sounds present in the various locales.
They found that the sounds of nature are still abundant throughout our national parks. About 75 percent of monitoring sites had animals audible more than 75 percent of the time. About 40 percent of the sites featured geophysical sounds, like running water, audible more than 75 percent of the time.
The most pristine soundscapes, featuring lots of natural sound and little noise pollution, were in remote locales of Hawaii, Alaska and the Pacific Northwest. But many recording sites in busier parks also reported high levels of natural sound. That’s good news, because the research suggests that humans still benefit from natural sounds mixed with anthropogenic sound. In several studies scientists mixed the sounds of running water or singing birds with unwanted noise, like traffic, yet subjects frequently reported positive responses to the natural sound, like feeling less annoyed and more tranquil. But scientists don’t know whether natural sounds actually help mask unwanted noise to the ear, or if visitors are simply able to enjoy them even when the sounds are paired with less desirable noise.
Noise also varies widely at the various locales inside each park. Yellowstone, for example, is very busy at major geysers and along the traffic-choked roadways. But outside of those heavily visited areas the levels of natural sound rise dramatically while human noise fades. Even busier park sites, the audio survey shows, contain pockets where unwanted noise levels are low and visitors can seek out the sounds of a waterfall, or the breeze blowing through the trees. That means even travelers who can’t often visit remote areas can enjoy healthier natural soundscapes.
In remote and urban parks alike, managing such soundscapes is a priority for the National Park Service, which seeks to steward them the same way they would scenic vistas, historic sites or park wildlife. “From a babbling brook to thundering waterfalls, birds singing or leaves rustling, natural sounds are part of a web of resources vital to park ecosystems and protected under the National Park Service Organic Act,” says Karen Treviño, who heads the the NPS Natural Sounds and Night Skies Division.
Managing noise to enhance natural sound can include rerouting traffic and parking, restricting access to motorized vehicles and aircraft or using hand tools in place of power tools. But solutions might also be as simple as reminding visitors to stop and open their ears. In response to increasing crowds and noise at Muir Woods National Monument, staff erected signs asking tourists to enjoy certain parts of the park quietly. “And people listened,” says Buxton.
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 that such efforts will be rewarded. “For me these sounds are treasures," she says. “They’re amazing natural resources, and how remarkable that they are also really good for our health and our well-being.”