When a Tree Falls in the Forest: How Man Made Noise Impacts WIldlife
If a tree falls in the forest, and no one is around to hear it, does it make a sound?
You don’t need humans to confirm the sound of a falling tree, or any noise for that matter, as scientists will tell you. The proof is in the behavior modifications that noise has caused in the forest’s wildlife.
The impact of noise on wildlife – from birds, to elk, to whales – has garnered plenty of attention from scientists in recent years. What may or may not be surprising is that studies are showing that animals with habitats in natural settings are modifying their behaviour in response to human noise.
You know that “fight or flight” instinct that we all experience when a door unexpectedly slams, cars collide, jackhammers tear up the street or an ambulance races by, sirens blazing? The “fight or flight” instinct in wildlife is being wildly over-stimulated, and although sometimes their behaviour modification is brief, it nonetheless happens. This is a real problem, as planet earth seems to be buckling to the impact of man-made noise on its ecosystems.
A 2009 article in Park Science describes animals reacting to human commotion in the reflexive manner of a creature suddenly threatened by predators. In humans, we know that these responses, when over stimulated for ongoing stretches of time, can lead to elevated blood pressure, stress, sleeplessness, depression and even heart disease. In wildlife, the constant flare-ups of anti-predator behavior interferes with their ability to perform normal functions, like foraging for food and taking care of their young.
The fear among scientists is that, as human-caused noise disturbances to wildlife become more frequent, populations of species could start to fade.
In Northern California – north of San Francisco, Muir Woods presents as a redwood-vaulted oasis, a place so silent that the air can be heard circulating around the redwood branches, and the gurgling of Redwood Creek is unmistakable and exhilarating. One of the first things visitors to Muir Woods National Monument in Marin County notice is a noise level monitor.
This place wasn’t always this quiet.
Back in 2001, Muir Woods had already been abandoned by the native otter population decades earlier, and pileated woodpeckers had abandoned the national park as well. A familiar pair of northern spotted owl – endangered species, in fact – were not frequenting the redwood cove as often as they once had, and park rangers were growing concerned.
Adding insult to injury, an asphalt walkway that had been installed was interfering with the growth of the redwood’s surprisingly shallow root systems, causing at least one of the redwoods – age somewhere between 500 and 1,200 years old – to fall.
Still, the man-made noise issue was the most worrisome, as the clamor of garbage can lids and park maintenance vans infested the park. Tying its proverbial noose, it seemed, was the park’s proximity to a metropolitan area of seven million people.
For decades, park rangers and scientists have been worried about the affects of human noise on wildlife, but little was done about it. Eventually, however, an effort to restore the Muir Wood’s natural sounds took hold.
Slowly, mechanical sounds were silenced, and park visitors followed suit. With a concerted effort, human noise was all but squelched. Signs posted near Cathedral Grove in the center of the park request silence from visitors. The decibel meter near the gift shop entrance that measures the voices of visitors had one park visitor commenting that they could see themself crunching on potato chips, as the decibel meter jumped with every crunch.
Today, there are times when the quiet in the park is so absolute, it seems possible to hear a banana slug slither by. According to scientists, this level of quiet is critical to the well-being of the native wildlife, which is recovering from the man-made cacophony that threatened its existence not too long ago.
Officials at some of the country’s national parks have worried about noise, and some have taken steps to make changes. Noise issues vary dramatically from one park to another. In the Florida Everglades, generators have been silenced at a campground, and park caretakers are trying to negotiate with airboat operators to measure the impact of their fans – which can mimic the sound of jet engines – to see if the noise they generate can be reduced. They have also approached officials at Homestead Air Force Base south of Miami about the timing of the sonic booms that shake the saw grass.
Noise reduction measures are being taken at some national parks, while there are high profile noise battles going on at others.
Park managers at the Grand Canyon want to require aircraft operators to shift to quieter planes, fly higher above the canyon’s northern rim, and refrain from flying at dawn or dusk. Senator John McCain, R-Arizona, has introduced legislation that would not only preempt the park’s plan to reel in aircraft noise, but would consider noise standards met if for at least 75 percent of the day, 50 percent of the park is free of commercial air tour noise.
Arizona environmental organizations have denounced McCain’s proposal, calling it a give-away to the air tour operators and an excuse to redefine what constitutes natural quiet.
A McCain spokesperson says the amendment was a measure to protect tourism jobs.
One of the most remarkable outcomes of the Muir Woods study comes from a year-long inventory taken of all sounds, natural and otherwise, in four places in the park. It was discovered that noise from the parking lot and gift shop bled a quarter-mile into the forest.
The parking lot was moved about 100 yards farther from the entrance, an ice machine was removed and the decibel meter was installed.
Park rangers are still establishing the affect that the reclaimed quiet has had on the park’s wildlife, since other clean up procedures were enacted at the same time, including removal of invasive weeds, elimination of the asphalt walkway, and installation of a new boardwalk that prevents visitors from walking on the forest’s spongy, porous moss-covered floor.
They say they don’t know the results yet. But otters have returned after a 74-year absence, and chipmunks are coming back as well.
In fact, two breeding pair of the rare, spotted nocturnal owls are inhabiting the Muir Woods site today.