Perhaps in addition to carrying bear spray, reading from a book of poetry (we’d recommend Mary Oliver or Gary Snyder) while hiking through bear habitat may ward off unwanted ursine advances. A recent study by researchers at the University of California, Santa Cruz, showed that human speech, in areas rarely visited by people, were terrifying to even mountain lions, the state’s apex predator.

We often hear that predators are more frightened of us than we are of them in the backcountry, and while this study can’t quantify who is more afraid of who, it does suggest there’s truth to that old maxim.

The scientists who conducted the research played recordings of people talking through speakers hidden in the trees and watched for animal response. Because it’s assumed the noisome clashing of the industrial sounds our civilization produces already drives wild animals away, the sound of human speech was the only thing broadcast. It’s as our mere presence alone was enough to frighten them.


Humans have become the most feared predators in nature, in other words.

At first, political pundit talk radio clips were played; understandably, when the animals heard it they quickly fled through the forest. Next, researchers read softly from books of poetry and nature writing and tracked the response. Still, the animals were nervous, watchful, and tended to run away. Mountain lions took off more than 80 percent of the time, in fact.

The sounds weren’t played all the time. But animals in the area learned the approximate areas of the speakers and tended to steer clear. When human speech was played through the speakers, animals from mountain lions to opossums changed their behavior. Some in the area made wholesale changes, increasing nocturnal activity or eating less, for example.

Changes like that percolate throughout ecosystems. Mice and other rodents take advantage of a lack of predators and their numbers can increase, as does the impact from their foraging. It stands to reason that this sort of behavioral impact happens in ecosystems wherever humans are present. Obviously, animals near where we have a massive presence become habituated, but what about out on the frontiers of our existence? Our presence in the backcountry, along trails and streamsides, may be having a bigger impact than we think.

We’ve seen the cascading effects of changes in predator behavior patterns before. When wolves were reintroduced to the Yellowstone ecosystem, for example. Wolves come in, predator and prey imbalances are restored, entire river systems change course, gradually, as flora and fauna adapt. Perhaps similar, but opposite sorts of changes take place when the mere presence of humans begins to drive predators away from regularly hiked trails.

“Pervasive fear of humans may also precipitate widespread community-level changes by disrupting natural predator–prey interactions,” says the report. “We suggest that the fear we human ‘super predators’ inspire, independently of our numerous other impacts on the natural world, may contribute to widespread restructuring of wildlife communities.”

“This study suggests that a conversation between two hikers can have a butterfly effect,” says Kaitlyn Gaynor from UC Berkeley, who was not involved in the study. “A mountain lion moves more quickly, an opossum changes its feeding habits, deer-mouse activity increases.”

Leave no trace just got a little more complicated.

Top photo: Priscilla du Preez

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