The National Park Service Organic Act mandates the preservation and/or restoration of natural resources within parks, including the acoustical environment. The acoustical environment can be defined as the actual physical sound resources, regardless of audibility, at a particular location.

Natural and Cultural and historic sounds are important components of the many National Park units. Natural sounds can include wildlife, water, vegetation, or weather sounds. These sounds are important to the protection of wildlife and their natural setting as well as visitor experience and enjoyment. The sound of a cannon shot echoing across a civil war battlefield or the hypnotic drumbeat of a sacred tribal dance provide visitors with insight into historic events or an earlier lifestyle, people, or culture. Cultural and historic sounds are treated and managed as a park resource with a truly unique and inherent value, and as an important component of the park experience for visitors.

National Parks were also created in part to allow the public to enjoy and appreciate the unique natural and cultural resources protected within our parks. Therefore, the sounds of people enjoying the parks through a variety of recreational activities are a common element of National Park soundscapes. Careful management will ensure that the sounds that contribute to our park experience are protected for current and future generations.

What is Soundscape?

A soundscape refers to the total acoustic environment of an area. Both natural and human sounds may be desirable and appropriate in a soundscape, depending on the purposes and values of the park. For example, the sound of canon fire and muskets may be appropriate and desirable at Gettysburg National Military Park but not in the wilderness of Yellowstone. Soundscapes often vary in their character from day to night and from season to season and can be affected by changes in numbers of visitors who introduce human-caused sound into the environment. The soundscape of a national park, like water, scenery, or wildlife, is a valuable resource that can easily be degraded or destroyed by inappropriate sounds or sound levels. As a result, soundscapes require careful management if they are to remain unimpaired for future generations.

How are Sounds Experienced?

Sound is defined as pressure variations or a wave traveling through the air that can be detected by humans and other animals. How we experience sound depends on two important characteristics: Frequency and Amplitude. The number of pressure variations per second in the air or the number of peaks and troughs in the sound wave is called the frequency of the sound and is expressed in hertz (Hz). Humans are usually able to hear sound with frequencies ranging from 20 Hz to 20,000 Hz. Amplitude is what we normally refer to as volume or loudness. As an object vibrates it creates sound waves and as it vibrates harder, the height of the wave, or the distance between the peaks and troughs in the wave, increases. This height (or the distance between the peaks and troughs in the sound wave) is known as the amplitude and is measured in decibels (dB). Most sounds contain numerous frequencies and each frequency can have a different amplitude. This complex combination of frequencies and amplitudes is how we experience the unique soundscape within a park.

Soundscapes and Science

The symphony of natural sounds within our national parks is an important natural resource and a critical component of the ecological communities that parks seek to preserve. Understanding the role of sound and acoustics in a healthy ecosystem is critical to their effective management and protection. Birds, insects, mammals, and amphibians rely on complex communication networks to live and reproduce. In habitats where wildlife vocalizations signify mating calls, danger from predators, or territorial claims, hearing these sounds is important to animal reproduction and survival. These types of issues are examined through research in acoustic ecology which is the study of sound in the relationships between organisms and their environment. Scientist also use bio-acoustics (bio=life, acoustics=sound) to determine the health of natural habitats. Scientists can discern details about animal populations and behavior by recording sounds in the wild. Such bio-acoustical recordings are used in a variety of ways, including bird censuses, bat echolocation studies, and marine mammal surveys.