Refuge Notebook 07-16-2010


Stop to hear the decibels

By Tim Mullet

One day in June, I sat at the bottom of a valley at the foot of a glacier in the Kenai Mountains. The wind blew steadily, rustling the leaves of small, stunted aspens, a river roared next to me, and off to my left, a waterfall, 500 feet tall, cascaded with a magnificent boom. I called to my colleague at the top of my lungs, “What a beautiful place!” Although he could barely hear me, he nodded with a smile. The sound surrounding us was almost deafening. Despite this, I felt the power of nature in all its wonderful glory. A few days later, driving on the Sterling Highway with my wife and kids in downtown Soldotna, I rolled down the window. The wind blew steadily and the traffic roared bye with engines and music booming. The sounds were deafening. I could barely hear my own voice when I commented to my wife of how loud everything was. We were surrounded by noise.

It is interesting how we, as humans, identify different sounds as pleasant, both as individuals and as a society. We choose different kinds of music, played at different amplitudes. Some of us buy vehicles that are quieter while others buy vehicles that are louder. Judging by my own experience, people also select certain areas for their sound quality, such as a secluded park, quiet fishing spot, or backcountry camp site. These sound values are important for identifying who we are, where we live, and what we prefer. Interestingly enough, the case is also true for wildlife. Birds, for instance, use sound to identify mates, define territories, and choose habitats. They have also been found to have reduced reproductive success and territory size in the presence of certain sounds, such as oil compressors. Identifying what sounds influence the landscape is an important topic for any person who seeks to enjoy a wilderness experience as well as any animal who lives there.

Noise is generally defined as unwanted or unpleasant sound. This definition implies that sound is qualitative. However, sound can also be measured quantitatively based on the amplitude of sound pressure, also known as a decibel (dB). Decibels are measured on a logarithmic scale – an increase of 10 dB doubles the perceived loudness. A normal conversation is typically 60 dB and hearing damage becomes prevalent at 120 dB. Your typical rock concert is generally 115 dB. A large waterfall would be recorded between 100-110 dB, whereas the Sterling Highway has been recorded to exceed 120 dB.

These sound pressures are derived from many different sources. During the summer, people and animals are bombarded by a range of decibels. In town we have road traffic and ATVs. In wilderness, we have planes, singing birds, and raging rivers. Winter provides less of an effect because of the insulating properties of snow, the reduced road traffic, hibernating wildlife, and aside from snowmachines, the lack of motorized vehicles in wilderness. These cacophonies of sounds are all attributes that define a landscape or what can be called a “soundscape.”

Currently, Kenai National Wildlife Refuge biologists are interested in mapping the soundscape of the Refuge. The intention is to map the distribution of decibel levels across the Refuge and identify whether the source of those decibels is human-made or produced by nature. We are doing this by placing sophisticated sound level meters out in the landscape to measure maximum and minimum decibel levels. For sound pressures that exceed a certain decibel level, we will digitally record the sound in order to identify its source.

Based on the spatial distribution of these sound samples, we will be able to create a map of sound sources within the landscape which we will use to predict where sounds occur across the Refuge and what those sounds are. This information will enable us to better understand how human-generated noise may be changing the natural soundscape.

We often times take for granted the effect sound has on our whole experience. Because we are typically surrounded by noise, we become habituated to those decibel levels, eventually ignoring or “tuning out” those sounds.

Taking a moment to listen to your environment may bring to light a new impression of what defines your surroundings and how you play a part. Perhaps you will discover the similarities between two types of sound sources or be able to compare the sound levels of your work place to those of your favorite fishing spot. In other words, identifying your own soundscape may give you a better appreciation of the environment in which you live.

The legislative purposes of the Kenai National Wildlife Refuge include conserving the natural diversity of wildlife and their habitats while providing opportunities for recreation. The conflict that sometimes arises between these two refuge purposes is not made any easier by the additional mandates imposed by the Wilderness Act of 1964. This legislation applies to 1.3 million acres of Congressionally-designated Wilderness within which the Refuge is tasked with “retaining its primeval character and influence” including “outstanding opportunities for solitude”.

Conserving the soundscape of the Refuge is imperative to both wildlife and visitors alike. So, perhaps next time you are out and about, instead of stopping to smell the roses, stop to hear the decibels.

Tim Mullet is a Ph.D. student in the Department of Biology and Wildlife at the University of Alaska Fairbanks working for the Kenai National Wildlife Refuge. His dissertation addresses the cumulative ecological effects of snowmachines. You can check on local birds or report your bird sighting on the Kenai National Wildlife Refuge Birding Hotline (907) 262-2300.