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Loud hikers cause wildlife panic more than off-road vehicles

DAILY SCIENCE

Shhh! Chatty hikers cause wildlife to panic even more than the racket of off-road vehicles

A Wyoming experiment reveals the way sounds of outdoor recreation affect wildlife, and the potential benefits of traveling quietly.
June 19, 2024

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It’s nice to hike through the woods with a few friends, feeling a little closer to the natural world. Perhaps you even entertain the idea of being in harmony with your surroundings.

It turns out, you might be more like a chainsaw at a chamber music concert.

The noise of a group of chatty hikers, it turns out, can set off panic among nearby animals. Their response is even more intense than if you drove a 4-wheeled offroad vehicle. And the effects can echo through the wilderness a week later, as wildlife avoid the site of even a small number of noisy human intrusions, according to new research.

“Noise from recreation can carry far beyond a trail system, so understanding how noise alone can affect wildlife is important for management,” said Mark Ditmer, an ecologist at the U.S. Forest Service’s Rocky Mountain Research Station who helped lead the study.

The woods are likely becoming a noisier place, as more people head outside to play. Last year a record 168 million Americans took part in outdoor recreation, according to the Outdoor Industry Association, a trade group. The pandemic lockdowns that closed many indoor venues is credited for boosting a trend that had already taken hold years earlier.

Outdoor recreation is often portrayed as leaving a light imprint on the natural world than. Sporting goods companies such as Patagonia tout their environmental credentials. The backcountry motto of “Leave No Trace” suggests humans can pass through a place without a mark.

But there is a growing realization that even the most low-impact activities can still affect wildlife. Increased human presence near wildlife is associated with a spike in stress hormones, abandonment of some habitat and drops in reproduction, among other things.

 

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But how much of an effect comes just from the

? And do different kinds of activities have different effects? A group of Forest Service researchers teamed up with colleagues from several universities to find out.

The scientists set up a series of experiments in the forests of western Wyoming, which draws thousands of visitors to nearby places like Grand Teton and Yellowstone national parks. They set up video cameras, audio speakers and motion detectors along trails created by wild animals, at least 650 meters from any place regularly traveled by people. When a creature passed a point on the trail, a video camera would start recording and a speaker located 20 meters away would begin broadcasting an audio recording of people engaged in an outdoor activity. That included hikers, mountain bikers, runners, and people riding offroad vehicles. In some cases, the audio was of a small group of relatively quite people. In others, it was groups of more than four talking a lot. The recordings lasted for up to 90 seconds.  All told, the speakers were triggered more than 1,000 times, with video capturing the reactions of mule deer, elk, moose, red fox, black bears, pronghorn antelope, cougars, coyotes and wolves.

When the scientists reviewed the images, it became clear that the sounds of outdoor recreation had a major effect. Wildlife was between 3.1 and 4.7 times more likely to flee when hearing those recordings than when they heard recordings of nature or nothing at all. They also showed signs of being more guarded and vigilant for 2.2 to 3 times longer after hearing recreation-related noises, the scientists reported last week in Current Biology.

The intensity of the reaction appears to have been influence both by how loud the sounds were and the type of sounds. Surprisingly, the effect of human voices outranked combustion engines. Recordings of talkative groups of more than four hikers or more than four mountain bikers triggered the strongest reactions, with animals 8 times more likely to run away. By comparison, animals were 3 times more likely to flee at the sound of offroad vehicles.

The effect was greatest among herbivores that are often prey animals, including elk, deer and antelope, as well as black bears. By contrast, large carnivores such as mountain lions showed little reaction.

The effect persisted. The week after speakers were shut off, the amount of wildlife showing up in videos was 1.5 times lower. This happened even though the amount of noise was low. Sound recordings were triggered no more than 21 times over the course of two weeks.

It’s not clear if these kind of behavior shifts would last, or if the animals would get accustomed to the sounds of humans. But public land managers need to pay attention to the potential effects, the scientists note. For instance, the study’s findings could help inform decisions about what limits to set on the size of groups allowed into certain areas, or efforts to educate people to reduce their noise. “Our findings highlight the need for thoughtful planning, with potential consideration of noise mitigation measures to minimize the impact on wildlife,” said Ditmer.

For those who aspire to leave wildlife less troubled, there is also some good news from the study. Small, quiet hiking groups or solo runners had little or no effect compared to the recordings of nature sounds.

Zeller, et. al. “Experimental recreationist noise alters behavior and space use of wildlife.” Current Biology. June 13, 2024.

Image: ©Anthropocene Magazine

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