It seems inevitable in summer. When we head out to the patio for dinner, to enjoy the evening air and quiet broken by chirping birds at the feeders, a neighbor seemingly sees it as a signal to cut his grass. The gutteral roar of his lawnmower carries well, and proves far more irritating than a mosquito's buzz in the ear.

During the day the mower's noise might have blended in with the rest of the background noise we create -- cars and trucks on the streets, weed-whackers, stereos, vacuum cleaners -- and not seemed obtrusive. But in the evening, a time many of us prize for relaxing and enjoying the day's end, a single mower can sound amplified.

Much the same can be said of noise in national park settings. In places such as Yellowstone, Glacier, Shenandoah, Great Smoky Mountains, Acadia, and Canyonlands, just to cite a few examples, we often expect the sounds of silence, or at least those of nature. But as I found out last year during a visit to Congaree National Park in South Carolina, society's background noises can intrude on these natural settings.

Now we're learning that there are at times unintended consequences of good deeds in national parks. For instance, efforts to reduce traffic by using shuttle buses can actually create a noisier environment, according to studies at Rocky Mountain National Park and elsewhere in the park system.

A study recently released by the Acoustical Society of America pointed to the shuttle buses in Rocky Mountain as just one example of noise generators in the park system.

A study in Rocky Mountain National Park in Colorado, for example, revealed the aural consequences of reducing traffic congestion on park roads by adding shuttle buses to carry people to and from trailheads. The new shuttles succeeded in making trails accessible to a greater number of visitors. But each bus was also six times louder than a car; and the sounds of chatting hikers, backpack zippers, and gravel-crunching boots became concentrated at bus arrival times instead of being spread more evenly throughout the day. This good decision therefore had a negative effect on soundscape, shrinking the visitors’ “listening area,” or the distance around their heads at which they can still hear natural sounds.

To mute, so to speak, these sound generators, a Colorado State University researcher, Peter Newman, and colleagues are developing soundscape models that park staff can use to help predict how management actions -- such as bringing in a fleet of shuttle buses to reduce air pollution and traffic -- can affect the soundscape.

Such "soundscape maintenance," notes Professor Peterson (who worked for nearly two years as a ranger at Yosemite National Park), is beneficial not just to human visitors in the parks but to the resident wildlife as well.

“[Animals] want to know, ‘Where’s Bambi?’” Professor Newman explains in a release sent out by the Acoustical Society. “‘How far away do I have to be where [my young] can still hear me … or where I can hear that vole crawling beneath the surface of the leaves?’”

The studies Professor Newman's team conducted included surveys of park visitors to get their thoughts on noise levels in national parks. And they found that something as simple as signs denoting "quiet zones" were effective in getting visitors to keep the noise down.

Professor Newman is presenting the findings of his studies this week in Hong Kong at a joint meeting of the Acoustical Society of America, Acoustical Society of China, Western Pacific Acoustics Conference, and the Hong Kong Institute of Acoustics.

“This paper is about lessons learned,” says the professor. “Not only is noise important to people, but if we ask people to quiet down, they will.”