STANDARDS

NGSS: Practice: Obtaining, Evaluating, and Communicating Information

Crosscutting Concepts: Cause and Effect

Core Idea:PS4.A: Wave Properties;
PS3.
A: Definitions of Energy;
LS4.D
Biodiversity and Humans

CCSS: RI.4: Determine the meaning of generalacademic and domain-specific words orphrases in a text.

It's YOU!

Humans make all kinds of sounds when they spend time in nature. Scientists recently studied how animals react. 

Illustrations by Tony Trimmer

Mark Ditmer/USDA

Mark Ditmer

Birds singing. Insects buzzing. Wind blowing through trees. These are some of the sounds you’d expect to hear in a national park.

There might be other noises too. Leaves crunching under a hiker’s boots. Bike tires skidding on a trail. Campers laughing while sitting around a fire. These human noises are familiar to our ears, even in nature. But how do they affect wild animals?

Mark Ditmer recently set out to investigate that question. He’s an ecologist with the U.S. Forest Service. That’s a government agency that manages large areas of public land across the U.S.

Noises in Nature

What is sound anyway? All sounds are created when particles of matter, like air, bump into each other. The resulting vibrations move in the shape of a wave. Your ears sense these sound waves, and your brain interprets them as sounds.

Many animals are adapted to sense very small vibrations. Some animals, like rabbits, have large ears that catch sound waves and direct them inside like a funnel. That helps them detect predators from far away. It also allows them to hear people that enter their habitat. 

Human activity can cause wild animals stress. In Wyoming, skiers have scared bighorn sheep away from feeding areas. And in Vail, Colorado, hikers have disturbed elk so much that fewer calves have been born. But scientists had never studied how much animals were bothered by the noises humans make.

iStockPhoto/Getty Images

VAST WILDERNESS  Mark Ditmer conducted his study in Bridger-Teton National Forest, a 3.4 million-acre area of western Wyoming.

Listening In

To study how animals respond to human sounds, Ditmer and his team set up an experiment. First, they made recordings of people doing noisy things in nature, like hiking, trail running, mountain biking, and riding all-terrain vehicles (ATVs).

Ditmer’s team placed speakers and cameras in wild areas of Wyoming’s Bridger-Teton National Forest. Sensors detected when an animal was near, and speakers played the human-made sounds. The cameras captured what the animals did. 

How did they react? And which noises bothered animals most?

Wild Reactions

Mark Ditmer/USDA

EXPERIMENT SETUP Ditmer attached cameras to trees to record how animals reacted to human sounds.

The scientists found that human sounds bothered some animals more than others. “Some ran immediately,” Ditmer says. “Others stood still, trying to figure out if the sound was a threat.” 

Elk and black bears were some of the animals that ran away quickly. Cougars, coyotes, and other large carnivores were less bothered. “The cougars could not have cared less!” says Ditmer.

The sound of big groups of hikers talking caused the most animals to run away. Animals were much less bothered by natural sounds, like birdcalls. Ditmer next plans to study how animals behave when they become used to human noises. 

This type of research can help forest managers make certain decisions, like where to build trails, that will not bother animals. People should enjoy nature, Ditmer says, but also try not to disturb wildlife. “Staying quiet lets you hear birds and other sounds you might miss.”

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