The Point Reyes National Seashore has below-average sound pollution in comparison to other lands managed by the National Park Service, according to a recent study based on data collected primarily by the park’s Natural Sounds and Night Skies Division. Yet the level of anthropogenic noise found in the seashore, which ranked in the 75 percentile, is still proven to have an impact on wildlife and the visitor experience.
The study, which analyzed thousands of audio clips collected by the division since 2005, was published last fall in collaboration with scientists from Colorado State University and the California Department of Fish and Wildlife. It examined 363 park units, representing half of the total area managed by the park service.
“Since the [park’s] inception, the U.S. population has more than tripled, road and aircraft traffic have become widespread, and 80 percent of the U.S. population now lives in urban areas,” the scientists wrote to introduce the impact of their findings, published by the journal Frontiers in Ecology and the Environment. “In this context, national parks represent refuges of ecological integrity and provide increasingly important opportunities for people to establish personal connections with natural environments.”
Nevertheless, the parks are far from protected from human noise.
The study used two sound thresholds, 10 decibels and 3 decibels, to categorize the level of anthropogenic noise above baseline sound—such as from wind, waves and wildlife—for each park unit. Overall, median noise levels caused by human activity were higher than 10 decibels in a third of the units, while the other 77 percent had median levels above 3 decibels. The seashore fell into the latter category.
Dr. Rebecca Buxton, the lead author of the study, described the implications of that number. “If you think about a 3-decibel increase above background, that’s a doubling of sound energy that actually results in a 50 percent reduction in listening area,” she said. “If you used to be able to hear all the natural sounds within a bubble of a 100-meter radius, now you can just hear them within a 50-meter radius.”
Dr. Buxton said there was strong scientific data to show that exceedances above 10 decibels—which amounts to a tenfold increase in sound—has significant impact on both human health and wildlife, while for noise above 3 decibels “there is most likely an effect, we just don’t have as much evidence.”
Nevertheless, the study cites research that does exist. For example, one study showed that noise at 3 decibels or greater can alter avian song performance, with detrimental outcomes for competition and pairing success. (As the noise grows, the research on the effect on birds shows lower survival rates and fitness and altered behaviors, including those that have broader effects on the ecosystem, such as seed dispersal and pollination.)
Another study at Grand Teton National Park—which came in at 2.97 decibels—found that noise from cars, bikes and pedestrians put elk and pronghorn at greater risk of being eaten by predators. The park is home to grizzlies, gray wolves and mountain lions.
There is also an impact on humans, according to the cited research. “At high levels of exposure, noise annoys people and contributes to health problems,” the study states. “At lower levels of exposure, noise reduces the benefits of experiencing natural sounds, which include increased relaxation, restored attention, improved mood, and reduced stress.”
Overall, the study found that the most common noise sources were aircraft and road vehicles, although when present, trains and watercraft generated the loudest noises.
For some of the parks, Colorado State graduate students combed through the recordings to determine exactly what the cause of the noise was, but those details are not available for Point Reyes and other low-ranking parks.
“Point Reyes is far enough removed from San Francisco that it is not getting the immediate impact of the noise,” Dr. Buxton said. “Somewhere like Golden Gate [National Recreation Area] comes out much louder. Also, there are not many roads in the park, it’s out of the flight path—there’s a lucky combination of factors here.”
G.G.N.R.A. came in at 6.24 decibels, while Muir Woods National Monument was 4.07. What are the factors that keep a hush over the seashore?
Out of its 71,000 acres, 33,373 belong to the Phillip Burton Wilderness—where the 1964 Wilderness Act minimizes roads and structures and prohibits the use of any type of motorized equipment or transport.
Although there are common commercial routes to and from local airports above the park, planes don’t drop lower than 3,000 feet over the seashore and the immediate area, according to a spokesman for the Federal Aviation Administration, Ian Gregor.
Additionally, the seashore is surrounded by waters protected by the Greater Farallones Marine Sanctuary, which regulates aircraft and boats.
Low overflight zones were first established by the National Oceanic and Atmospheric Administration in the ’80s and ’90s over the Farallones, with minimum altitudes, typically 1,000 feet, for commercial and recreational planes, helicopters and drones. (Confirming the impact of this policy, a 2007 United States Fish and Wildlife study on the impact of aircraft and boats on common murres in Marin concluded that most disturbances by aircraft occurred below 1,000 feet and that helicopters were more disturbing than fixed-wing planes.)
Several years ago, there was a local effort to expand the protected zones, which do not cover the entire sanctuary. Many of the proposed areas would have connected or extended existing overflight zones, which include at the mouth of Tomales Bay and at Double Point in Bolinas. But the changes were never adopted due to push-back from pilots and discord in the working group tasked with providing recommendations.
Maria Brown, the superintendent of the Greater Farallones, told the Light that she has not nixed the proposal altogether, though the working group was disbanded. Pending further review, adopting them in the future is still under her discretion.
By water, another sanctuary regulation helps lower the noise. Mary Jane Schramm, a Farallones spokeswoman, said in 2000 the sanctuary prohibited the use of jet skis throughout its jurisdiction, including Tomales Bay.
“This prohibition is primarily to protect wildlife from disturbance and injury from close approach, but it also eliminated noise and pollution from the two-stroke engines of the times. [Motorized personal watercraft] back then spewed large quantities of hydrocarbons, carbon monoxide, and smoke, and roared across the water,” Ms. Schramm wrote to the Light.
The prohibition of jet skis “helped to create a ‘culture of quiet’ in the seashore,” she said.
In the Point Reyes National Seashore compendium, there are several additional sound mandates. Day users of established trails within wilderness areas may not travel in groups larger than 40. “Large groups create noise and a presence that disturbs wildlife and interferes with other people in the area who are looking for a wilderness experience away from crowds and noise,” the compendium states.
Park biologist Dr. Ben Becker pointed to another seashore policy that prohibits the use of any audio or mechanical device to attract or disturb wildlife. That policy states, “The use of audio devices to attract wildlife has the potential to cause bodily injury, energy loss, a decrease in food intake, habitat avoidance and abandonment, and reproductive losses.”
But for Dave Press, the seashore’s wildlife ecologist, “It’s all relative.” “In a smaller park with no wilderness area, there’s a potential to be completely swamped with sounds coming from outside the park,” he said. “But clearly, unnatural noises here can still be detrimental to the visitor experience and can disturb natural processes. Owls calling to each in the middle of the night as a big commercial airliner is coming into San Francisco—that disturbs those natural activities.”
The recent sound study identifies situations where noise management would yield the greatest benefits to park visitors and wildlife. For example, it found that the park service’s loudest spot is Chamizal National Monument, a small park near downtown El Paso that is bordered on three sides by highways. Theodore Roosevelt Inaugural National Historic Site in Buffalo, N.Y., ranks second noisiest, and Little Rock Central High School National Historic Site in Arkansas ranks third. Fourth is the White House. All of these places are more than 100 times louder than they would be without human activity.
Yet even the quietest park, Cedar Breaks National Monument—an isolated canyon in Utah— was not devoid of human interference, coming out at 1.24 decibels above baselines.