Effects of Noise

A Great Gray Owl perched on a branch of a pine tree.
Great Gray Owls use their very sensitive hearing to locate prey.

Photo by Joe Medley.

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

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 et al. 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 et al. 2009).

In general, a growing number of studies indicate that animals, like humans, are stressed by noisy environments (Shannon et al. 2015). 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 (Ware et al. 2015).
Photo of a tree and birds. Three domes are superimposed over the tree. representing listening area for the birds.
Schematic representation of how masking reduces an animal's listening area. As background sound increases, the area in which the perched bird can hear important sounds, represented by the domes, is reduced.

Photo by Ted E. Dunn

These findings are especially significant because national parks are under increasing noise pressure. Noise levels in park transportation corridors today are many times the natural level (Mennitt et al. 2015). Air transportation can also 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 much as 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.

Learn about a predator that uses incredibly sensitive hearing to locate its prey.

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

Visitors

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 and 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 et al. 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 and can interfere with how people rate landscapes in national parks (Weinzimmer et al. 2014). 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 et al. 2009). Tranquility, it turns out, even in the most remote areas of our national parks, is becoming increasingly scarce.

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


Actors as soldiers fire the cannon during a Civil War battle reenactment
Actors as soldiers fire the cannon during a Civil War battle reenactment

NPS Photo

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.

The acoustical environment of national park cultural and historic sites, therefore, is an important part of the setting 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 parks' purposes and mitigate extraneous noise.

References

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

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

Fuller, R., Warren, P., Gaston, K. (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.

Mennitt, D., Fristrup, K., & Nelson, L. (2015) A spatially explicit estimate of environmental noise exposure in the contiguous United States. Journal of the Acoustical Society of America, 137(4), 2339-2340.

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

Parris,K., Velik-lord, M., & North, J. (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

Shannon, G., McKenna, M., Angeloni, L., Crooks, K., Fristrup, K., Brown, E., Warner, K., Nelson, M., White, C., Briggs, J., McFarland, S., & Wittemyer, G. (2015). A synthesis of two decades of research documenting the effects of noise on wildlife. Biological Reviews. Article first published online: 26 JUN 2015 DOI: 10.1111/brv.12207

Ware, H., McClure, C., Carlisle, J., & Barber, J. (2015). A phantom road experiment reveals traffic noise is an invisible source of habitat degradation. Proceedings of the National Academy of Sciences,112(39), 12105-12109.

Weinzimmer, D., Newman, P., Taff, D., Benfield, J., Lynch, E., & Bell, P. (2014). Human responses to simulated motorized noise in National Parks. Leisure Sciences 36(3), 251-267

Last updated: June 9, 2017