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Running out of room in the wild, bears sometimes wander into human neighborhoods, like this black bear in Alberta, Canada. (Nick Norman / National Geographic Stock)

Animal Highways

Can scientists protect animals by connecting their habitats?

A grizzly bear and her cub stand on the edge of the forest. In front of her, a wide bridge covered in trees arches over a highway. Across the bridge lie sweet berries. They’re food the pair needs. Will the bears use the bridge to cross the highway and get the food?

The bears face a problem that many wild animals experience today. The highway divides their forest habitat. Crossing it is dangerous. Sometimes, towns, businesses, or parks fragment animals’ habitat. This can cause wild animals to have troubling runins with people.

For scientists, the tree-covered bridge is a possible solution. This wildlife corridor may help animals travel safely. They can get over or through places where human activity has broken up their habitat. Some wildlife corridors are overpasses or underpasses that allow animals to cross highways. Others are narrow strips of land that connect one piece of wilderness to another that’s miles away.

Scientists have been building wildlife corridors for about 50 years. But now scientists are wondering: Are these animal highways actually helping populations grow and stay healthy?


It was a rainy summer day in southwestern Canada in 1991. Scientists trapped a wolf they named Pluie (ploo-WEE). They fitted her with a radio collar. It would send them signals showing Pluie’s location. Then they let the wolf go.

Over the next two years, the scientists tracked Pluie’s journey. They were amazed by where she went. Pluie crisscrossed parts of Canada and the American Northwest. The wolf roamed a total area of 40,000 square miles.

Scientists learned an important lesson from Pluie. Animals like wolves need to roam huge areas of land in order to thrive. But people need land for building homes and businesses. Can animals and humans survive in the same place?


Pluie’s story inspired a conservation group. It’s called Yellowstone to Yukon, or Y2Y for short. The group protects more than 80,000 square miles of land in the northwestern United States and Canada. Bears, wolves, cougars, elk, and many other animals live there.

Many people also live in the Y2Y area. There are highways, houses, and malls. To help animals and humans live together, Y2Y built corridors that help animals cross highways. It also created trails that weave through towns. The trails connect one area of habitat to another.

Scientists wanted to see if animals would use these corridors. They put in cameras to watch for animal traffic. The results looked promising. Scientists filmed elk, deer, bears, and wolves passing through. But some scientists have questioned whether corridors are working as well as many believed.


In northern Australia, two groups of rats live in nearby patches of forest. The rats belong to the same species. One patch is connected to the other by a thin strip of trees. The rats use the corridor to move back and forth between the two areas.

In 2005, scientists took DNA samples from some of the rats. They found that the two groups of rats were not trading genes. The rats were moving through the corridor, but they weren’t mating with rats on the other side. This led to low genetic diversity among the rats. As a result, the rats might have trouble surviving diseases or other threats in the future.

“Just because the corridor is there doesn’t mean it’s working,” says biologist Andrew Gregory. Gregory is trying to figure out why some animals use corridors to find mates and others don’t.

Gregory and other scientists are studying corridors around the world to find out what makes certain ones successful. They want to know how to build corridors animals will use. Then they’ll be able to help save some at-risk species from dying out.

This article originally appeared in the February 2013 issue of SuperScience. For more from SuperScience, click here.

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