For the more information about natural sounds and night skies in the National Park Service, please visit http://www.nature.nps.gov/sound_night/.


Effects of Noise

The summaries below will provide you with an idea of the importance of sound and the impacts of noise to wildlife, visitors, and cultural and historic resources.

Wildlife

Schematic representation of how masking reduces an animal's listening area.
Schematic representation of how masking reduces an animal's listening area. As background sound levels increase, the area in which the perched bird can hear biologically significant sounds, represented by the domes, is reduced. Photo by Ted E. Dunn

That old expression, "The early bird gets the worm," turns out to be truer than ever in urban settings today. In fact, recent studies are finding that some birds in noisy environments have taken to singing at night in order to be heard over the din of the city (Fuller et al., 2007).

Sound, just like the availability of nesting materials or food sources, plays an important role in the ecosystem. Activities such as finding desirable habitat and mates, avoiding predators, protecting young, and establishing territories are all dependent on the acoustical environment. In order to continue with these activities, animals are being forced to adapt to increasing noise levels. Research shows that males of at least one frog species are adapting to traffic noise by calling at a higher pitch (Parris, Velik-lord, & North, 2009). This could be problematic for the females, because they prefer lower-pitched calls, which indicate larger and more experienced males. Human-caused noise has produced similar results in multiple bird species (Barber, Fristrup, Brown, Hardy, Angeloni, & Crooks, 2009).

In general, a growing number of studies indicate that wildlife, like humans, is stressed by a noisy environment. The endangered Sonoran pronghorn avoids noisy areas frequented by military jets; female frogs exposed to traffic noise have more difficulty locating the male's signal; gleaning bats avoid hunting in areas with road noise (Barber et al., 2009). When these effects are combined with other stressors such as winter weather, disease, and food shortages, sound impacts can have important implications for the health and vitality of wildlife populations within a park.

Great Gray Owl
Great Gray Owl. Credit: Joe Medley

These findings are especially significant because national parks are under increasing noise pressure. Noise levels in park transportation corridors today are at 1000 times the natural level (Barber et al., 2009). Air transportation, as well, can affect life on the ground. Sound levels during peak periods in a high air traffic corridor in the Yellowstone backcountry, for example, were elevated by up to 5 decibels. The result is as muchas a 70% reduction in the size of an area in which predators can hear their prey (Barber et al., 2009).Increasingly, careful consideration of the impacts of human-generated noise on wildlife is a critical component of management for healthy ecosystems in our parks.

To learn more about a predator that relies on very sensitive hearing to locate its prey, click here.

An Annotated Bibliography of the Effects of Noise on Wildlife can be found on the Useful Resources page.

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Visitors

"As the din of modern society continues to grow, the need for refuge from noise and clamor are becoming increasingly important." National parks must strive to "help meet that need by providing places of calm and quiet where people can still hear the wind in the trees, the rhythm of nature, and the beat of their own heart..."
[Monroe et al., 2007, p. 25]

Our world is getting noisier. With dramatic increases in traffic, the explosion of digital gadgets (think of your buddy's constantly chirping Smartphone) and our increasing capacity to reach once-remote areas, quiet solitude is a diminishing commodity. Not surprisingly then, the American public comes to parks with natural quiet in mind. They come for the soothing effect of a gurgling stream, a delicate bird song, or the rustle of leaves on a fall day. From the awe-inspiring thunder of a waterfall to the gentle rustle of leaves in the breeze, natural sounds have a subtle but profound impact on visitors. In fact, 72% of Americans say one of the most important reasons for preserving national parks is to provide opportunities to experience natural peace and the sounds of nature (Haas & Wakefield, 1998).

However, natural quiet in parks is increasingly at risk. To study the effects of human-caused noise on visitors, volunteers at Muir Woods National Monument cataloged all sounds they heard, day and night, for a year. What they found was surprising. It was rarely quiet (Monroe, Newman, Pilcher, Manning, & Stack, 2007). Parks are experiencing an on-going acoustic assault by everything from air tours to maintenance equipment. Such noise affects visitors' perceptions of solitude and tranquility. In a related study at Muir Woods, visitors found increasing levels of human-caused sounds to be unacceptable and even annoying (Monroe et al., 2007). Noisy visitors, loud talking, and other related sounds were found to substantially detract from the quality of the visitor experience. In other studies, noise has been shown to be more disturbing to visitors if it is loud, occurs in bursts, is unpredictable, or if it interferes with quiet activities such as bird watching.

Isolated areas are not exempt. In Grand Canyon, no single location is totally free of aircraft noise, and in some areas it can be heard up to 43 times in a 20-minute period. Backcountry hikers, after September 11, 2001, reported knowing that something was very wrong because there were no sounds from commercial aircraft (Bell, Mace, & Benfield, 2009). Tranquility, it turns out, even in the most remote areas of our national parks, is at stake.

An Annotated Bibliography of the Effects of Noise on Visitor Experience and Soundscapes can be found on the Useful Resources page.

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Cultural and Historic Resources

"And the rockets' red glare, the bombs bursting in air..." These words tell a story about our country's fight for freedom and have a powerful effect on millions of Americans. The specific sounds associated with our history or cultural heritage not only teach us about the past, they connect us to distant times and places in a way that few other things can.

tribal drumming
NPS Photo

The acoustical environment of national park cultural and historic sites, therefore, is an important part of the ambiance and helps create meaningful connections. The silence of an empty cell on Alcatraz Island hints at the sense of isolation of a former inmate. Cannon fire or Taps at a Civil War battlefield conjures images of both pride and sadness. Every unit within the national park system has its own cultural soundscape that is both unique and appropriate to that particular place. From the brassy horns of New Orleans Jazz to hypnotic native drumming, no two are the same. Unwanted or inappropriate sounds, such as aircraft, vehicles, and construction equipment, can detract from the experience. With this in mind, the National Park Service manages park units to protect those cultural and historic sounds considered fundamental to the park's purposes and mitigate extraneous noise.

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References

Barber, J. R., Fristrup, K. M., Brown, C. L., Hardy, A. R., Angeloni, L. M., & Crooks, K. R. (2009). Conserving the wild life therein: Protecting park fauna from anthropogenic noise. Park Science, 23(3), 26-31.

Bell, P. A., Mace, B. L., & Benfield, J. A. (2009). Aircraft overflights at national parks: Conflict and its potential resolution. Park Science, 26(3), 65-67.

Fuller, R.A., Warren, P.H., Gaston, K.J. (2007). Daytime noise predicts nocturnal singing in urban robins. Biology Letters, 3, 368-370.

Haas, G., & Wakefield, T. (1998). National parks and the American public: a national public opinion survey on the national park system. National Parks and Conservation Association and Colorado State University, Washington, D.C. and Fort Collins, CO.

Monroe, M., Newman, P., Pilcher, E., Manning, R., & Stack, D. (2007). Now Hear This. Legacy Magazine, 18(1), 19-25.

Parris,K. M., Velik-lord, M., & North, J. M. A. (2009). Frogs call at a higher pitch in traffic noise. Ecology and Society, 14(1), 25. Retrieved from http://www.ecologyandsociety.org/vol14/iss1/art25