Though much remains to be done, the Park Service has already made significant progress in combating noise. A propane-fueled shuttle system in Zion National Park has reduced traffic jams and carbon emissions and also made the canyon quieter. In Muir Woods, library-style "quiet" signs help keep the volume down; social scientists have found (somewhat to their surprise) that the ability to hear natural sounds—15 minutes away from San Francisco and in a park celebrated mostly for the visual magnificence of its trees—ranks high with visitors. In Sequoia and Kings Canyon National Parks, which have a major naval air station to the west and a large military air training space to the east, park officials take military commanders on a five-day "Wilderness Orientation Overflight Pack Trip" to demonstrate the effects of military jet noise on visitor experience in the parks. Before the program started in the mid-1990s, rangers reported as many as 100 prohibited "low flier" incidents involving military jets every year. Now the number of planes flying less than 3000 feet above the ground surface is a fourth to a fifth of that. Complaints are taken seriously, especially when, as has happened more than once, they're radioed in by irate military commanders riding on jet-spooked pack horses on narrow mountain trails. In that context, human cursing is generally regarded as a natural sound.
Sometimes the initiative to combat noise has come from outside the park system. Rocky Mountain National Park, for example, has the distinction of being the only one in the nation with a federal ban on air tour over-flights, thanks mostly to the League of Women Voters chapter in neighboring Estes Park. Park Planner Larry Gamble took me to see the plaque the League erected in honor of the natural soundscape. It was in the perfect spot, with a small stream gurgling nearby and the wind blowing through the branches of two venerable aspens. Gamble and I walked up a glacial moraine to a place where we heard wood frogs singing below us and a hawk crying as it circled in front of snow-capped Long's Peak. But in the twenty minutes since we'd begun our walk, Gamble and I counted almost a dozen jets, all in audible descent toward the Denver airport. I'd flown in on one of them the day before.
The most intractable noise problem in our national parks comes from the sky. The reasons for this are both acoustical, in terms of how sound propagates from the air, and political. The skies above the parks are not managed by parks. All commercial air space in the US is governed by the Federal Aviation Administration, which has a reputation for safeguarding both its regulatory prerogatives and what is often referred to in aviation parlance as "the freedom of the skies." Passengers taking advantage of that freedom in the United States numbered around 760 million last year. But much of the controversy about aircraft noise in our parks has centered on air tours.
A twenty-year dispute over air-tours above the Grand Canyon has involved all three branches of the federal government and, for protraction and difficulty, makes the court case in Bleak House look like a session with Judge Judy. A breakthrough seemed likely when the Grand Canyon Working Group, which includes representatives of the Park Service, the FAA, the air tour industry, environmental organizations, tribal leaders, and other affected parties, eventually managed to agree on two critical points. First, the Park Service's proposal that "the substantial restoration of natural quiet" called for in the 1987 Grand Canyon Overflights Act meant that 50 percent or more of the park should be free of aircraft noise 75 percent or more of the time (with no limits established for the other 50 percent). They also agreed on the computer model of the park's acoustics that would be used to determine if and when those requirements had been met. All that remained was to plug in the data.
The results were startling. Even when air tour overflights were factored out entirely, the model showed that only 2 percent of the park was quiet 75 percent of the time, due to noise from hundreds of daily commercial flights above 18,000 feet. In other words, air tours could be abolished altogether and the park would still be awash in the noise of aviation. Those findings came in over two years ago. The Park Service has since redefined the standard to apply only to aircraft flying below 18,000 feet. The Working Group has yet to meet this year.
Noise can be characterized as a minor issue. The pollution of a soundscape is hardly as momentous as the pollution of the seas. But the failure of an animal to hear a mating call—or a predator—over a noise event is neither insignificant nor undocumented. (One 2007 study shows the deleterious effects of industrial noise on the pairing success of ovenbirds; another from 2006 shows significant modifications in the "antipredator behavior" of California ground squirrels living near wind turbines.) On the human side, the inability of a park visitor to hear 10 percent of an interpretative talk, or the inability to enjoy natural quiet for fifteen minutes out of an hour's hike—as the Grand Canyon plan allows—does not mean that the visitor understood 90 percent of the presentation or that the hiker enjoyed her remaining forty-five minutes on the trail.
In dismissing the effects of noise, we dismiss the importance of the small creature and the small human moment, an attitude with environmental and cultural costs that are anything but small. Not least of all we're dismissing intimacy: the firsthand knowledge and love of living things that can never come exclusively through the eye, the screen, the windshield—or on the run. This struck home for me in a chat with several members of the League of Women Voters in a noisy coffee house in Estes Park, Colorado. I'd come to learn more about the air tour ban over Rocky Mountain National Park and ended by asking why the park and its natural sounds were so important to them.
"Many people just drive through the park," said Helen Hondius, straining to be heard above the merciless grinding of a latte machine, "so for them it's just the visual beauty." For Hondius and her friends, however, all of whom walk regularly over the trails, the place needed to be heard as well as seen. "It's like anything else," Lynn Young added, "when you take the time to enjoy it, the park becomes a part of what you are. It can shape you."