Why did the cougar cross the road?

by Michele Regenold

Have you ever accidentally hit an animal on the road? Maybe a sparrow didn’t fly high enough or a raccoon froze in your headlights or a deer tried to leap over your car. There’s an awful sound. Your breath catches in your throat.

Stupid critter, you may think. What were you doing in the road? Like the old joke about why the chicken crosses the road, the answer is probably simple—to get to the other side. There may be food or water or shelter there. Maybe a mate or young ones.

Experts in a new field called road ecology say that road kill affects wildlife populations in just 1–2 generations. Road kill of rarer species such as cougars and bears can have major consequences on local populations.

In addition to road kill, roads and highways can also create barriers to animal movements. As a result, wildlife habitat becomes fragmented, which divides populations into smaller groups. “If there’s no movement between them, certain populations can blink out,” says Tony Clevenger, research wildlife biologist with Montana State University’s Western Transportation Institute.

Take wolves, for example. Their disappearance from certain ecosystems would “have cascading effects,” Clevenger says. Without wolves, there’d be less pressure on deer. They would graze more and over-browse the vegetation. That could lead to erosion, allowing more silt in streams, which would affect water quality. A whole chain of events occurs when one “keystone” species disappears, and ultimately that affects human beings.

Besides being a practical and safety concern for people and wildlife, “it’s a social responsibility to maintain our natural heritage,” Clevenger says.

Helping wildlife cross roads safely

Yellow deer crossing signs are one of the most common ways that transportation agencies have tried to warn drivers about areas where wildlife crosses the road. But researchers have concluded that the standard deer warning signs basically don’t work.

“Deer don’t read well,” jokes Tom McDonald, safety engineer at Iowa State University’s Center for Transportation Research and Education. He believes that if drivers simply paid more attention to their driving, there would be a lot fewer deer hits.

Research is being done on other kinds of driver warning devices, like systems that detect the presence of large animals. Research is also being done on ways to change animal behavior, such as fencing to prevent animals from crossing roads, and underpasses and overpasses designed to help animals cross roads.

Wildlife crossings in Banff National Park

Banff National Park, located in the Canadian Rockies, is “really a one of a kind laboratory,” says Clevenger, who’s been studying Banff’s wildlife crossings since 1996. *The park was the first in North America to use such a large number of wildlife crossings to help improve motorist safety and connect habitats for wildlife.

Banff, which spreads over 2,564 square miles of southwestern Alberta, Canada, is home to numerous large mammals, including grizzly bears, black bears, wolves, coyotes, cougars, moose, elk, deer, bighorn sheep, wolverine, and lynx.

Wildlife crossings were added in Banff beginning in 1981 when parts of the Trans-Canada Highway were upgraded from 2 lanes to 4. This reconstruction included building 24 wildlife crossings—22 underpasses and 2 overpasses. The crossings were designed to connect habitat and allow safe passage for large animals.

In addition to the crossings, 8-foot-tall fences were also installed on both sides of the highway to cut down on animal-vehicle collisions. And it worked. The fencing reduced animal-vehicle collisions by 80%. It cut road kill of deer and elk by 96%. The average number of elk-vehicle collisions per year dropped from about 100 to 6.

The fencing prohibited animals from crossing the highway. Clevenger says that for a while, some animals walked along fences to the end and crossed there. This created “hot spots” of animal-vehicle collisions, but the overall number of collisions still declined. Eventually animals learned to use the wildlife crossings, which are spaced about a mile apart and are positioned in natural crossing areas.

Long-term research

To learn more about the crossings and the animals that used them, researchers began long-term monitoring of crossings in 1996. From 1996–2006, 10 species of large mammals have used the crossings in Banff more than 84,000 times.

Each crossing has a track pad, a raked section of earth that spans the width of the crossing and is about 6 feet long, to catch imprints of animal tracks. The track pad tells researchers what species are using the crossings, what direction they traveled, and the number of individual animals.

Researchers check the crossing structures every 3 days year round and regularly rake the track pads clean. They’ve also deployed infrared-operated cameras at several crossings.

To learn more about the number of individual animals using the crossings, researchers stretched 2 strands of barbed wire and sticky string across an underpass to snag hair samples. They especially focused on bears. The hair samples provided DNA, which allowed researchers to identify each individual, including its sex and ancestry.

Using the same hair sampling technique, a new study began in 2006 to learn more about the effectiveness of the wildlife crossings. Do they encourage genetic diversity? Do they keep animal populations connected? Scientific data will help answer these questions.

It’s clear from the crash statistics that the wildlife crossings have improved safety. Wouldn’t it be great if the crossings also help improve, or at least maintain, wildlife populations over the long term?

About the jobs

Road ecology is such a new field that it’s not a subject you can major in in college. Not yet, at least. But it’s a dynamic, growing field. Whether you’re interested in biology, nature conservation, engineering, or transportation planning, there will be plenty of opportunities for young people to pursue. Keep your eyes open and be creative.

Clevenger says that one thing that’s attractive about road ecology is that transportation agencies are often receptive to making transportation projects more sustainable for wildlife.

Road ecology also changes, depending on the landscape. Out west, it’s about preserving landscapes to protect habitat linkages and corridors so large predators and their prey species can move freely. In more heavily farmed areas like the Midwest, much of the remaining native habitat may be along the roads, and those are important nature reserves.

Learn more

To learn more about road ecology, see www.coe.montana.edu/wti/road_ecology/home.php

*Correction

This statement was corrected on Oct. 1, 2007. It originally stated that "The park contains the longest stretch of highway (45 km) in the world . . ." This is no longer correct. The state of Montana on Interstate 93 has or soon will have more wildlife crossings.