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Hikers and skiers might want to think twice before criticizing motorcyclists and snowmobilers for disrupting the environment.

Research recently compiled by Colorado State University found virtually every type of outdoor recreation has potential to harm wildlife, with

non-motorized activity showing more documented negative effects than motorized sports.

The findings were part of a scientific review published Dec. 8 that looked at the effects of recreation in protected areas on wildlife.

It revealed some potentially uncomfortable results for people operating on the assumption their quiet, human-powered activities are less harmful than loud sports such as snowmobile riding.

“I’m a hiker and skier,” said Courtney Larson, one of the authors of the paper. “It is kind of a tough issue for this group of people, including myself.”

Larson said the findings are particularly important because in the United States alone from 2000 through 2009 the number of people participating in outdoor recreation increased 7.5 percent and the number of visitor days increased 33 percent.

And recreation, particularly when human-powered, is frequently marketed as a key component during the creation of protected areas.

“It is something that people don’t realize is happening,” Larson said. “If we don’t understand how recreation can be affecting wildlife then we are not really conserving wildlife as effectively as we could be.”

To reach their findings authors of the Colorado State paper identified 2,306 scholarly articles dated from 1981 through 2015.

After tossing out papers with “obviously irrelevant” records such as tourism research with no wildlife component they were left with 403 articles.

They further whittled the list to 274 articles from around the world by zeroing in on research that covered “non-consumptive uses,” and focused on effects of particular activities, such as skiing, instead of recreation infrastructure, such as ski lifts. It didn't include consumptive uses such as hunting and fishing. Nor did it include effects of motorized recreation on plants and soil.

Overall, 93 percent of the papers documented some effect of recreation on wildlife and 59 percent of the effects were classified as negative.

“Recreation and conservation are not always compatible for all species in all places,” said Sarah Reed, Wildlife Conservation Society scientist and Colorado State faculty affiliate, another one of the authors in a video on the project.

Some research from Lake Tahoe and the Great Basin they reviewed included a 2011 study from the Lake Tahoe Basin on the Northern Goshawk, a 2008 study from the Lake Tahoe Basin and Sierra National Forest on the effects of snowmobiles on martens, a 2007 study from University of Nevada that looked at the effects of off-highway vehicles on western fence lizards in the western Great Basin and a 2013 study from Yosemite National Park that looked at the effects of park recreation on Great Grey owls.

“We tried to get everything that was out there the best we could,” Larson said.

The results seem to challenge conventional wisdom when it comes to recreation and wildlife.

For example, 40.3 percent of studies showed non-motorized activities, which included 15 activities such as hiking, alpine and cross country skiing, camping and biking, showed negative effects while only 34 percent of studies of motorized recreation on land and snow showed the same.

Negative effects included decreased species richness or diversity, decreased survival, reproduction occurrence or abundance, decreased foraging, decreased weight or increased evidence of stress.

Wolverines, coyotes, bobcats and guanaco, a camelid native to South America, showed behavioral responses to non-motorized activity but not to motorized activity, according to the paper.

The recreation category with the highest rate of negative effects was “winter terrestrial activity,” which included motorized and non-motorized sports.

Studies of winter terrestrial activity showed “negative” effects on wildlife at a rate of 64.4 percent, compared to 39.6 percent negative for activities from all seasons.

While the study didn’t cover why they found a higher rate of negative effects from recreation on snow the authors had some ideas.

They said it could be that during winter wildlife is already closer to the brink and human intrusions more damaging.

“Movement away from recreationists may be more energetically costly in snowy conditions,” the authors wrote. “There could also be habitat effects since vegetation in alpine and sub-alpine environments regenerates slowly, so habitat degradation caused by winter recreation could be more severe than that caused by other recreational activities in more temperate climates.”

The research also showed how land and wildlife managers could benefit from more research.

Birds, particularly corvids, a group that includes crows and ravens, had more evidence of positive effects, possibly because they are good at adapting to humans.

Rodents were among mammals that fared well in the face of human intrusion, possibly because they, too, tend to adapt well.

Less than one-half of 1 percent of articles covered by targeted journals studied effects of recreation on wildlife.

And the research that does exist is biased toward North America and Europe with other parts of the world underrepresented.

There is also a bias toward mammals and underrepresentation of amphibians and invertebrates, even though they tend to show more negative effects based on the Colorado State research compilation.

The authors cautioned that the relatively small amount of research on the subject meant they were working with a small sample size and more research could produce more useful data.

“Protecting biodiversity from potentially harmful effects of recreation is a primary concern for conservation planners and land managers who face increases in park visitation rates; accordingly, there is demand for science-based information to help solve these dilemmas,” they wrote.

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