Wildlife is more sensitive to humans than previously thought

ELI FRANCOVICH Idaho Statesman

We have a people problem.

That was the message received by Laura Prugh of the US Park Service in Glacier Bay, Alaska, several years ago. To Prugh, who studies human-wildlife interactions in relatively populous Washington state, the claim seemed a bit far-fetched.

After all, only 40,000 people visit the 3.2-million-acre park annually, absurdly low numbers for anyone used to reveling in waterfalls in Washington or Oregon, for example.

In fact, Glacier Bay is only accessible by boat or plane, and 94% of visitors arrive by cruise ship. But park service employees reported increasing numbers and wanted to know how, or if, that trend was affecting native wildlife. So Prugh, an associate professor in the University of Washington School of Environmental Sciences and Forestry, visited the site.

“I was surprised how few people there were,” he said. “And I thought ‘Wow, these people have really lost perspective on what a lot of visitors are.'”

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Still, he agreed to do the study. Over the course of two summers, she collected images from 40 motion-activated cameras at 10 sites focusing on wolves, black bears, grizzly bears and moose. She expected to find little or no “difference in animal activity between high-use sites and low-use sites.”

In a study published this month, Prugh and his co-authors found that if humans were present, the cameras detected fewer than five animals per week across the four species studied. In most cases, this probably meant that animals avoided areas where humans were present. Second, in rural areas, wildlife detections dropped to zero each week once outdoor recreation levels reached the equivalent of about 40 visitors per week. The researchers note that in some places where animals are more habituated to humans, the reaction to human presence will be less.

While it’s just one study, in one place, the findings have implications for recreation management.

“Our study indicates that if people want to recreate and minimize their impact on wildlife, they might actually be better off hiking on more crowded trails because those sites disturb wildlife anyway,” he said. “I think, unfortunately, there’s a trade-off between the human experience and the impact on wildlife.”

A developing field

The question of how, or even if, human outdoor recreation of the non-game variety impacts wildlife is “sort of an emerging field,” Prugh said. Despite their relative youth, numerous recreational ecology studies have shown that animals change their behavior in response to human presence.

Some mammals have become more nocturnal, foregoing their normal daytime routines in hopes of avoiding human presence. In Montana, wolverines and bighorn sheep avoid areas where backcountry skiers slide. Wild reindeer are fleeing farther from backcountry skiers than from snowmobiles, according to another study.

All of that is well documented; What hadn’t been looked at, however, was the minimum disturbance threshold, or, in simpler terms, how many humans it takes to send a grizzly packing, said Joel Berger, a Colorado State University professor and author of ” The It is better to eat you with: Fear in the animal world”.

The UW study begins to answer that question, he said. Berger was not part of Prugh’s study and has not met her, though he said he admired her research.

“In my opinion, Prugh’s study provides the first quantitative evidence on the responses of wildlife species when exposed to people in these low-density situations,” he said.

He said it also showed variation in species response to human activity, noting that Prugh’s study found moose were more active if people were around, indicating that large ungulates were using human presence as a shield against more cautious animals, such as wolves. That’s known as the human shield hypothesis, a term coined by Berger.

“The question is, what does it take for animals to learn?” he said. “To be able to adopt this riot strategy against harassment and predators.”

In addition to those questions, the study also poses a conundrum for recreation planners and outdoor enthusiasts, both in remote and more urban settings.

Implications for recreation

Balancing recreation and wildlife is something Spokane County park planner Paul Knowles often considers.

“As a land manager, you sacrifice some areas, in a sense, so that other areas can be dedicated primarily to wildlife habitat,” he said.

When county planners design and build trails, they try to include “wildlife disturbance buffers.” These shock absorbers are built using the best available science on how much space species need from humans. However, in a built-up environment like Spokane County, it is not always possible to include that space.

Anecdotally, at least, Knowles said she has heard “over and over again” that once the county acquires property and develops it for recreation, wildlife sightings plummet.

“We acquired these conservation areas for multiple purposes and multiple benefits, including recreation,” he said. “So we have to find a way to balance them. It’s hard.”

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