Even in the wilderness, humans are creating noise pollution that poses a threat to wildlife and natural serenity, according to a first-of-its-kind study by scientists at Colorado State University and the U.S. National Park Service.
The scientists found that manmade sounds created noise levels that were twice as high as background natural sounds in almost two-thirds of the nation’s parks and protected areas.
There was a 10-fold or more increase in noise pollution in a fifth of these areas because of manmade sounds, the scientists reported in Thursday’s issue of the journal Science. They analyzed millions of hours of sound measurements from 492 sites around the U.S.
While the research team did not disclose its data from specific Bay Area locations, the presence of a large airport like San Francisco International Airport significantly contributes to the region’s racket, said lead author Rachel Buxton of the Department of Fish, Wildlife and Conservation Biology at Colorado State University.
“With one of the busiest airports in the U.S., SFO is definitely a driver of noise pollution,” she said.
New Federal Aviation Administration flight paths have caused an uproar in the once-serene Santa Cruz Mountains, as well as other parts of Santa Clara, San Mateo, Santa Cruz and Alameda counties, triggering a lawsuit and floods of complaints. Residents have formed more than a dozen new community groups in the South Bay alone, bearing names such as Quiet Skies NorCal.
Other major sources of noise are highways, industry and the cacophony from residential communities.
At Muir Woods in Marin County, where noise levels were becoming unacceptable for most visitors, park officials have created a “quiet zone,” asking people to lower their voices and turn off music. This approach has reduced sounds by almost 3 decibels.
To be sure, noise is expected at some urban parks like San Francisco’s Dolores Park because they are popular and festive places to gather, said George Wittemyer, an associate professor at Colorado State University and another author of the study. And despite the region’s overall noise, there are parts of the Bay Area that are not under airplane routes and remain serene, such as Marin County’s Mt. Tamalpais and parts of the East Bay Regional Park District, as well as Big Sur, Wittemyer added.
Noise pollution can have a harmful effect on wildlife by reducing the ability of prey to hear predators approaching, or interfering with predator’s ability to hear prey such as insects and mice. It also masks bird songs and calls, which reduces their ability to defend resources, find a mate and breed.
Previous research has found that noise causes an overall decline in the richness of species. A study of a gas extraction sites with loud compressors, surrounded by silent woodlands, found that 32 different bird species nested in the quiet areas, while only 21 species nested in noisy sites.
Even plants can be affected by noise pollution if seed-eating animals change their behavior or location because of the sound pollution.
To quantify the extent of noise pollution across the U.S., particularly in protected areas designed to be safe havens for biodiversity, the team recorded sounds at 492 sites across the country. They used a computer algorithm to establish a baseline, or natural sound level, for the various areas.
They found that human noise doubled the background sound levels – exceeding 3 decibels – in 63 percent of protected areas. It caused a 10-fold or greater increase in background sound – exceeding 10 decibels – in 21 percent of protected areas.
In other words, noise reduced the area that natural sounds can be heard by 50 to 90 percent. This also means that what should be heard at 100 feet away could only be heard from 10 to 50 feet away, they reported.
Although wilderness areas were found to have the lowest exposure to noise pollution, 12 percent of these areas still experience human-made sound levels that were 3 decibels above natural levels, the authors report.
The expansion of human activities and transportation networks into the furthest reaches of remote areas is delivering noise to once-quiet locales, they said.
Some protected areas have not only created “quiet zones” like Muir Woods, but also launched shuttle services to cut back on traffic as well as aligned flight patterns over roads rather than wilderness.
The research team said it does not want to disclose its findings about noise pollution at each of the Bay Area’s individuals sites because the information “may be misinterpreted” by the public – suggesting there is a problem when there is not, Wittemyer said. But the team will share the data with park authorities if they request it, he said.
“The point of this is to flag the issue and get people aware of it,” Wittemyer said. “We encourage people to get out and listen to the landscape they are in – experience not only the visual environment, but the sound environment.”