Right off a Wyoming game trail, a black bear walks through the Bridger-Teton National Forest. A motion-sensor camera, placed there by researchers, picks up its movements and triggers the sounds of bikes racing through the dirt, played by audio speakers. The wildlife scatters.
The scene set up for a two-year study mimicked a realistic encounter animals have with humans, Katherine Zeller, a U.S. Forest Service researcher, told the Idaho Statesman. The study, conducted by the Forest Service in collaboration with Boise State University, used motion-sensor cameras connected to audio playback systems to observe the impact of recreational noises on animal behavior, and found that the sounds may have long-term effects on animals and can cause wildlife to flee the area — sometimes for as long as a week.
The consequences of recreation on wildlife have been difficult to study, in part because researchers have found it challenging to control the environment, Jesse Barber, a Boise State professor who authored the study, told the Idaho Statesman. But when Zeller and Mark Ditmer, both researchers for the Forest Service, discussed ways to study that impact, Ditmer, who had worked with Barber in the past, invited him to brainstorm — and they came up with a plan.
The team set up their system at 20 spots in four different areas near game trails in the Bridger-Teton National Forest along the Idaho border. When an animal triggered the motion sensor, a recreational sound would play 20 meters away. In 2022 and 2023, the researchers captured everything that triggered the cameras, from large carnivores to smaller prey.
When wildlife heard the sounds, many would flee or be on alert, similar to a normal predator response. Quicker noises, such as mountain bikes, caused many animals to be vigilant rather than flee. They seemed to be deciding whether the sound was a threat, Ditmer said. Fleeing is considered a stronger response, Ditmer told the Statesman, leaving high-resource areas and missing important food sources.
“I’m not going to join any large hiking groups. That’s for sure,” Ditmer told the Statesman.
ANIMALS REACT DIFFERENTLY NEAR POPULAR TRAILS
While all recreational noises scared the animals, whether it was a vehicle or a bike, large groups of hikers elicited the strongest reaction. Their responses can affect their long-term health, Barber said, since animals that are fleeing or looking for a predator aren’t eating as much.
The sounds also had a long-lasting effect. After leaving, animals often avoided the area for over a week. For a low-traffic hiking path that winds through a large area, “one person a day is going to change which wildlife is present,” Barber said.
How their findings apply to animals near popular hiking spots is still unclear. The team plans to look at how animals get used to recreational noises over time — a term called habituation.
Barber said in his experience, some animals don’t get used to humans. In a study that Barber was involved in, they looked at how birds responded to traffic noise at Lucky Peak State Park in Boise over two years. The birds didn’t seem to get used to the car noises. Many of them left completely, and the ones that stayed ate less, Barber said.
Some species were more afraid of the noise than others. In the Wyoming study, elk were the most likely to flee, Zeller told the Statesman, while cougars weren’t as bothered: “They were either curious or didn’t care,” Zeller said.
“There is an increased need to understand the impacts of recreation on our public lands to protect wildlife,” Zeller said.
WILDLIFE RESPONSES CAN HELP TRAIL MANAGEMENT
The team thinks knowing more about how animals respond to humans could inform future policy decisions and help preserve wildlife.
As populations grow, outdoor recreation has been increasing. COVID-19 only furthered this trend, especially for backcountry activity, Barber said. Unlike heavily trafficked trails, animals in the backcountry aren’t as exposed to humans, and building new trails in areas where people aren’t usually found could have negative impacts on wildlife, he added.
Zeller said she hopes their research could help forest managers make more informed decisions, allowing them to understand the “true footprint” of trail expansion and consider the species most sensitive to recreation.
“Land managers are really facing this dual mandate of trying to provide recreation opportunities for people, but also protecting those natural resources like wildlife on their land,” Zeller said. “So we’re hoping that providing information will help them make decisions to do that.”
To reduce harm to wildlife, Barber recommends implementing a permit system to help reduce heavy traffic on trails.
Barber also suggested that hikers walk quietly to mitigate the negative effects on wildlife. He said experiments have shown that “when the world was quieter, people heard more birds, they experienced more wildlife.”
Walsh covers science news for the Idaho Statesman for the summer of 2024, thanks to the American Association for the Advancement of Science Mass Media Fellowship. She is a graduate student in the Department of Biochemistry and Molecular Biology at the University Of Nevada Reno.
