by Gussie Fauntleroy

On extremely dry, warm, windy days at the Great Sand Dunes National Park and Preserve, a particular set of conditions causes the sand itself to emit a haunting, low-pitched sound. Not the whistling of wind over sand, but a sustained low frequency groaning, like that of a cello. Fred Bunch, resource management specialist at the park, has heard this “singing” of the sand as it shifts and moves. For Bunch, the fact that the sand itself can be heard is all the more reason for doing everything possible to protect the natural quiet that contains this sound.

The Great Sand Dunes is among the quietest of the American national parks, a quiet less degraded by high visitor numbers and the motorized noise of bus traffic and air tours than many parks in the system. But the Sand Dunes’ natural soundscape is extremely vulnerable. To illustrate the impact of increased human-made sounds on such an environment, Bunch uses the analogy of adding spoons of dirt to an already muddy glass of water. The difference after one more spoonful is negligible, but stir a single spoonful of dirt into a pristine glass of clear water, and the difference is dramatic.

In an effort to establish baseline data documenting the park’s current ambient soundscape, including natural and human-made sounds, the National Park Service’s Natural Sounds Program, based in Ft. Collins, has conducted acoustic monitoring of selected sites within the park. In 2008 the first recordings took place over about 12 days in the northwest corner of the park near the Baca National Wildlife Refuge. (Previous monitoring in 1993 and 1994, prior to the establishment of the Natural Sounds Program, employed less sensitive and sophisticated recording equipment and methods.)

The 2008 measurements document the fact that the Sand Dunes area is “on par with some of the quietest places in the country,” according to Emma Lynch, an acoustic resource specialist with the Natural Sounds Program. The ambient natural sound level at night in the monitored area was less than 15 decibels and about 17 decibels during the day. For comparison, the average sound level in a library is 40 decibels. The recordings also picked up long periods of elk bugling and coyote calls, while dominant non-natural sound was from aircraft, audible almost 60 percent of the time during daylight hours.

A follow-up set of monitoring at the Sand Dunes was done during the summer of 2009, focusing on additional sites and continued for longer recording periods of 25 days each. The data from these recordings has not yet been processed, Lynch says, adding that the she and her colleagues hope to have results available by sometime this winter.

One way the soundscape data will be used is to aid park management in creating a sound (as in noise) management program to mitigate intrusive human-made sound, notes Great Sand Dunes National Park Superintendent Art Hutchinson. Park officials also will rely on the data when addressing the U.S. Air Force in response to proposed low-level training flights out of Cannon Air Force Base.

In addition the acoustic data will come into play as Lexam Explorations begins its new environmental assessment on the impact of oil and gas exploration in the Baca National Wildlife Refuge, as well in gauging the potential acoustic effects of large tracking solar arrays such as that being proposed in Saguache County by Tessera, Hutchinson said.

While human-made sound levels affect the experience of visitors to the Great Sand Dunes, increased background noise can also adversely impact wildlife. A paper titled “Animal listening area and alerting distance reduced by moderate human noise” (Barbar, Crooks, Fristrup) was published in a recent issue of Trends in Ecology and Evolution. The paper is based on collaborative work by the NPS Natural Sounds Program and researchers at Colorado State University. It cites studies that indicate even “moderate” increases in background noise can affect such matters of animal survival as foraging, anti-predator behavior and reproductive success.

The authors propose a new approach to gauging the impacts on wildlife: understanding how increased background noise reduces an animal’s “listening area,” or the distance over which it can effectively hear and distinguish sounds that are vital to its survival. For example, a rise of three decibels in background noise, barely perceptible to humans, can reduce an animal’s listening area by 30 percent.

Hutchinson has his own conception of a “listening area,” based on a memorable experience a few years ago. Standing in a remote area of the park, he realized that a sound reaching his ears was the bell at the Nada Carmelite Hermitage just south of Crestone. If he could hear the ringing of a church bell from several miles away, he thought, sound must travel farther across the Valley than he previously believed. In fact, the topography surrounding the Sand Dunes creates a basin where cool air pools, allowing sound to travel over especially large distances.

Gordon Hempton, an international acoustic ecologist, Emmy Award-winning sound recordist and author, spent time in the Great Sand Dunes in 1990 and again about 10 years later. Hempton lives in the Northwest and has been recording natural soundscapes worldwide and passionately advocating for quiet for the past three decades. During his second Sand Dunes visit he noticed what he describes as a “significant deterioration of both the natural soundscape and the natural quiet” in the park. He attributes the changes to increased numbers of visitors, noisier visitor behavior and increased air traffic.

While Hempton respects the efforts of the NPS Natural Sounds Program, he takes a broader, less decibel-oriented approach to the impact of noise in the natural environment. He notes that the peak range of human sensitivity to sound falls between 2 and 5 kilohertz, a high-pitched range more associated with bird song than human speech. As a result, he strongly disagrees with the widely held assumption that our ears have evolved primarily to pick up human speech. He sees intrinsic value in preserving quiet at a level most people today have never experienced.

“We need to recognize in a deep ecological sense that we evolved to hear the sounds of nature,” Hempton says. He points out that early nomadic humans would have known to travel in the direction of greater bird song, an indication of water and resources for survival. “We’re connecting to a larger purpose in life, to a deep heritage and to the future. A lot of the meaning of life comes at the thresholds of sound.”

Bunch and others in the National Park Service believe those threshold sound levels need to be quantifiably measured in order to protect quiet at the Sand Dunes and other parks. “It’s critical that we have data that is reproducible, and we’re trying to establish that,” he says. “We need to establish a good baseline and then we can revisit it to indicate trends.”

With air traffic being the primary source of noise pollution in backcountry areas—the FAA predicts air traffic nationwide will double or triple by 2025—Hempton stresses that the world’s first civilian no-fly zones must be created over national parks. “We need legislation that expresses the American will, which is to reclaim the national park system,” he asserts. “We need to remind ourselves how national parks are even more important today than when they were established.”

Gussie can be reached at