Not-So-Silent Nights, Soundscapes, and Acoustic Monitoring
story and photos by Karen L. Monsen
Listen to the voice of nature, for it holds treasures for you.
~Native American (Huron) Proverb
In a world bombarded with sounds, people seek tranquility in national parks and wilderness areas. In 2013, the Journal of Environmental Psychology reported survey results from 15,000 visitors to 39 National Park Service Areas and found “…91% considered enjoyment of natural quiet and the sounds of nature as compelling reasons for visiting the parks, second only to viewing the scenery (93%).”
Responding to public comments on noise, the National Park Service (NPS) established a Natural Sounds & Night Skies Division, “…to protect, maintain, or restore acoustical environments throughout the National Park System.” In 2010, Zion NP established its Soundscape Management Plan and other parks did the same. With a handful of acoustic and social scientists involved in soundscape research, the NPS is monitoring natural and human-caused sounds to identify ways to reduce noise, maintain natural sounds, and improve the park experience.
Noise and Natural Sounds
Music to one’s ears is noise to another’s. Distinctions between pleasing sounds and “noise” are subjective, with “noise” generally described as undesirable sounds accompanied by negative emotions such as annoyance, fear, and mild anger. The University of Pennsylvania School of Medicine found noise effects on the cardiovascular system include hypertension and stroke, and associations between environmental noise on sleep disturbance and children’s cognition. Experimental psychologist and Southern Utah University professor Britton Mace explains, “Human-caused sounds have steadily increased over the past 100 years, in urban and suburban areas especially, creating a cacophony of noise.” Conversely, natural sounds are associated with reducing stress, improving cognitive function, and eliciting positive emotional states.
Do You Hear What I Hear?
To reduce unwanted noise, the NPS began monitoring sites to identify and quantify human-made and natural sounds. Monitoring acoustic data involves measuring amplitude (loudness) expressed in decibels (dB) or decibels adjusted to human hearing (dBA) and frequency measured in hertz (Hz). Humans can sense sounds with 0 dB at 1 kHz even though they cannot distinctly hear the sound. At above 85 dB, employers must provide workers with hearing protection. Conversational speech is around 60 dBA, a whisper might be 20 dBA, a vacuum cleaner 70 dBA, an overhead jet 120 dBA, and a rock concert can reach above 125 dBA. Decibels increase exponentially—with a 10 dB increase, the perceived loudness intensifies tenfold.
For animals, human-generated sounds can interfere with basic survival—masking sounds used to establish territories, avoid predators, and protect young. When animals cannot hear important acoustic clues, an owl might not hear a mouse, a bird misses hearing an insect, or a chipmunk cannot hear an approaching coyote. For humans, man-made sounds obscure the soothing waterfall, wind-rustled leaves, or an impending storm.
The second acoustic measurement is frequency, measured in hertz (Hz). Humans hear between 20 Hz and 20,000 Hz. For comparison, dogs hear up to 45,000 Hz, bats navigate using ultrasonic vocalizations at 120,000 Hz, and elephants produce infrasound too low for humans to hear.
Monitoring equipment deployed at various NPS and BLM locations typically include a microphone (with bird spike), digital recorder, batteries, sound pressure level dB-meter, and a weather station. Along with weather data, the recording unit captures sound levels and frequency readings from 12.5 to 40,000 Hz and typically creates a 24-hour archive for 30 days.
In the past two years, Dr. Mace collected acoustic data at 14 locations across the expansive Grand Staircase-Escalante National Monument (GSENM) and accumulated nearly 17,000 recording hours. Naturalists examining these recordings have identified specific bird calls, coyotes, three different cricket species, hiker voices, and over-flying planes.
The National Parks Service Soundscapes website includes acoustic data collected at various locations. The Great Sand Dunes NP was the quietest place with 8.7 dBA, remote Grand Canyon trails registered whisper-levels of 20 dBA, thunder at Arches NP registered 100 dBA, a military jet flyover produced 120 dBA, and some of the quietest places in GSENM registered between 13-15 dBA.
Dr. Mace is building an online sound library and creating a GSENM visitor soundscape kiosk linking acoustic recordings to specific locations on an interactive map. The sound library and soundscape kiosk are scheduled for completion in 2017. By educating people about soundscapes, Dr. Mace hopes to increase support and interest in sound research, attract undergraduates to SUU’s work, and define exciting new soundscape projects.
From acoustic monitoring, we know that even following a snowy day in Zion National Park, the soundscape reveals a not-so-silent night.
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