What's a Safe Distance Between Humans and Wildlife?

Spending time in nature is good for people, but when humans head outdoors, wildlife can suffer.

Outdoor recreation—from mountain biking to hiking—has been known to have negative behavioral and physiological effects on wildlife. Human encroachment in wildlife habitat can lead to issues with survival and reproduction rates and ultimately drops in population.

But natural resource planners and outdoor managers don’t have scientific research in order to form helpful distance guidelines to keep wildlife safe.

For a new review published in the journal Nature Conservation, researchers looked at nearly 40 years of studies that looked at the impact outdoor recreation had on wildlife. 

The review was part of a broader study looking at the impacts of recreation on wildlife in the last remaining wildlife corridor remaining across the Sonoma Valley in California.

“The review was the portion of the study trying to attain recommendations for the threshold distances to people and visitor numbers when wildlife begin to show impacts from people,” study co-author Jeremy S. Dertien, a Ph.D. candidate in wildlife biology at Clemson University, tells Treehugger.

“Previous field work in Boulder County, Colorado, and lessons learned from my co-authors really piqued my interest in how recreation can dictate when and where different species will use their habitat.”

As an example, Dertien says, in Boulder, they didn’t detect species like the dusky grouse in prime habitat where mountain biking was permitted. But they did find them in some sub-prime areas where mountain biking was not allowed.

“Even somewhat anecdotal evidence like that grouse finding motivates you to dive deeper into the issue and try to get answers to some of the difficult questions,” he says.

Measuring Distance of Disturbance

For the review, Dertien and his colleagues sifted through 330 peer-reviewed studies from 38 years and found 53 that fit the quantitative threshold they were looking for.

There were many ways that the authors measured the distance that human disturbance had an impact on wildlife.

“Most were observing at what point an animal flees from human presence (e.g., walk towards a shorebird, once it flies measure the distance from where you are standing to where the bird was) and a few others had GPS or radio collared animals and the researchers could model the distance at which animals were changing their behavior from humans,” Dertien says.

The team notes that the distance varied depending on the animal type. For shorebirds and songbirds, the uncomfortable distance to people was as little as 328 feet or less. For hawks and eagles, it was more than 1,312 feet.

The distance varied even more for mammals. The human impact was felt at just 164 feet for some small rodents, while large ungulates like elk were affected when they were about 1,640-3,280 feet from people.

“Overall, different species have different evolutionary reasons to become vigilant or frightened at different distances or from different stressors,” Dertien says. “Much of it can be attributed to the ability to safely flee in the case of large animals like elk vs. rabbits or eagles vs. songbirds.”

The most obvious way that wildlife responded was to run away, but there were other ways that human activity had a negative effect.

“Most of the negative impacts were wildlife individuals fleeing from a person Other impacts that were seen were reduction in the relative abundance or presence of a species,” Dertien says. “Increase in heart rate and stress hormones have been seen with human disturbance, but we only found one threshold paper that looked at heart rate.”

Hiking or Biking?

And the type of human activity can also have a different impact. Walking quietly possibly may be less stressful than someone zipping through the woods on a bike.

“Previous research has shown some mixed results. What we saw was that hiking-only recreation had a notably smaller zone of influence than other non-motorized or motorized recreation types. In other words, trails that only had hiking seemed to have a smaller footprint on the environment surrounding the trail,” Dertien says. “However, this was not statistically significant, which was likely due to the wide variety of recreation types versus the sample size in our review.”

The researchers hope the findings will help planners create guidelines and buffers so people can enjoy outdoor recreation without damaging the animals that already live there.

“It is easy for most people to assume that when you are out in nature that all the other animals around you are not really affected. But we know that many species change their behavior, become distressed and may reproduce less depending on the recreation type, the distance from the disturbance and the magnitude of the disturbance. All of which can reduce wildlife populations,” Dertien says.

It’s key to understand the distance where human activities begin to affect nature.

“Finding these thresholds where recreation begins or ends to negatively impact wildlife allows for the planning and management of park infrastructure (e.g., trails, restrooms) and visitor numbers in a way that respects people’s ability to enjoy nature while ensuring that all the species of wildlife have some portion of the protected areas were they are not stressed by human presence,” Dertien says. “This could include making sure there is a wide buffer between different trails to leave gaps in the wilderness where there is little human disturbance.”