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Perilous Crossings

Wildlife movement in Greater Yellowstone is extraordinary but every day with busy highways it's becoming extraordinarily more tenuous

Black bear crossing the road near Obsidian Creek; NPS / Diane Renkin
Black bear crossing the road near Obsidian Creek; NPS / Diane Renkin
Why do we need large, living landscapes where animals are free to move?

I’ve spent much of my life pondering this question, in conversations that were started by my Dad and uncle and shared by my siblings and cousins. It’s why, I suppose, so many of us became scientists or, at the very least, naturalists.

To start with, consider that the very definition of an animal involves movement. Webster’s New Collegiate Dictionary defines an animal as “A multicellular organism of the kingdom Animalia, characterized by the capacity for locomotion, fixed bodily structure, restricted growth, nonphotosynthetic metabolism, and an ability to recognize and respond to stimuli.”

In terms of locomotion, the wild animals that we are familiar with move across landscapes to meet daily, seasonal, and lifetime needs. They don’t take trips casually or solely to explore. Such movements are necessary for survival of individuals and the persistence of the population and species. 

Movements occur across a wide range of scales from daily movements (measured in inches to miles) to seasonal migrations (tens to thousands of miles) to lifetime movements (covering thousands upon thousands of miles in sum).  In today’s fragmented world, the farther an animal tries to move, the more difficult it usually becomes, especially if the animal tries to cross highways or roads.

Many other types of human development are virtually impassable for wildlife. As we humans have altered the environment to suit our own needs, we have taken habitat from other species and created barriers to their movement. In brief, one of the worst aspects of human progress has been the steady diminishment of the rest of the animal kingdom.

What we have in the Greater Yellowstone Ecosystem as a collective phenomenon of wildlife movement and the large animals that comprise it is unprecedented in the Lower 48. Yet how much we take for granted, and if we take it for granted we pay less attention to the factors that could jeopardize its persistence.

As the Director of the Craighead Institute, I have been involved in several projects which looked at animals that experienced fatally the danger that highways pose.

Dr. Lance Craighead
Dr. Lance Craighead
We studied roadkill on Bozeman Pass in Montana over a 10-year period, recording locations where carcasses were found. We gleaned a lot of insight from where animals died. Some of the stories are harrowing.

One incident occurred late at night on May 10, 2000. There would be snow the next day, but at that time of night there was just a cold drizzle. Water puddled on the pavement of U.S. Interstate 90, connecting Bozeman and Livingston, and blasted into the bushes beside the highway as cars sped past.

A young male mountain lion, weighing about 125 pounds, had been waiting in the shadows on the south side of the freeway for several minutes, but he had run out of patience. 

He could probably smell the strong scent of deer across the highway, but couldn’t see them. He had made his way down the steep, rocky slope behind him through thick Douglas Fir and Engelmann spruce stands, along a faint game trail made by mule deer and elk.  He had been secure and comfortable walking through the forest at night, but when he reached the highway he stopped. 

The bright lights of speeding vehicles and the loud noise of the traffic frightened and confused him. He waited. Eventually though, his drive to move overcame his caution as the traffic near him eased off.  Suddenly he dashed across the empty eastbound lane and reached for the top of the Jersey barrier—a three-foot-high concrete wall in the center of the Interstate. In one fluid movement he sailed across it toward the hidden space on the other side: leaping into two approaching pairs of headlights.

Behind the first set of headlights, Dr. James Allard, a professor of Philosophy at Montana State University, was heading home to Bozeman in the right lane in his 1997 Subaru Outback with his wife. 

He was driving below the speed limit, keeping his eyes open for deer, but glancing into his rearview mirror at the pickup that was beginning to pass him.  As he swung his gaze forward again he quickly glimpsed a patch of tawny fur just before he felt the impact.  His body slammed forward when the lion and the front of his car collided.

Jim’s airbags deployed instantly and cushioned the blow on him and his wife, but the lion was not so lucky; the impact broke the grill and the cat was tossed up and into the windshield, breaking the glass all the way across before bouncing off the left side of the window. 

As soon as he hit the pavement he was run over by the passing pickup.  The driver of the pickup first saw the cougar in mid-air, flying over the barrier and bounding once in front of his truck.  He barely had time to feel relieved that the cougar had gone past him before it was back and under his tires.

The drivers of both vehicles struggled for control.  They were racing side by side, between a cliff face and a cement wall, in the dark, on wet pavement, and Jim was pinned back by the air bag.  He managed to hit the brakes and pull the car onto the narrow shoulder.  He knew he had to get off the highway and out of the traffic.  The pickup did the same a bit farther down the road.  Even the cougar, with his last strength, pulled his shattered body toward the shoulder and away from the deadly stream of traffic.

The occupants of both vehicles were startled, and frightened, but they were also concerned about the lion.  Jim’s wife had seen the animal raise his head as they sped past.  After he pulled over and stopped on the shoulder Jim walked back to look at the lion.  It was close to death, and out of the way of traffic, which was still speeding past.  There was nothing he could do for the cougar, but he called 911 to report it. 

The dispatcher passed the news on to the Montana Department of Fish and Game, and before long a highway patrol cruiser and a truck from the Montana Department of Fish and Game arrived.  The accident was duly recorded and the cougar carcass was hauled away.

Biologists working for the Craighead Institute in Bozeman later recorded it, a datapoint, as a mountain lion road-kill at milepost 316. The accident ended up costing Jim $5,000 in repairs. It cost the cougar his life.  

The accident left such an impression that Jim clearly remembered the details of it three years later. Animals like the cougar are killed because they need to move across the landscape and because humans need to move across the same landscape.  Our high-speed travel routes are often lethal barriers to the movements of other species.
Highways represent death traps for many species.  A mountain lion becomes another casualty of the Interstate-90 corridor on Bozeman Pass between Bozeman and Livingston. Photo courtesy Lance Craighead / the Craighead Institute
Highways represent death traps for many species. A mountain lion becomes another casualty of the Interstate-90 corridor on Bozeman Pass between Bozeman and Livingston. Photo courtesy Lance Craighead / the Craighead Institute
Why would an animal risk crossing a highway that is so obviously dangerous? Why would a cougar leave the wild country in the central part of the Greater Yellowstone Ecosystem to head north into its northern flanks? 

It’s an inquiry that applies to many different animals and there are many  possible explanations.

One contributing factor to accidents such as this comes from the biology of species like mountain lions. Adult animals establish territories (or home ranges in the case of bears) where most other animals of the same species are unwelcome.
 
As young animals grow up and leave their mothers they are forced to search around for a favorable place to live.  Some, like female grizzlies, stay close to home. Others, like male sub-adult grizzlies, move away or range farther in seeking to establish their own territories. If they stumble across an occupied territory they could be injured or killed by the resident male. So they move away, even farther from the place they grew up. They may move hundreds of miles before they find a place. Or they may never find one. Or get killed crossing a road.

Fifty years ago, such dispersal movements were rare in the Greater Yellowstone Ecosystem; mountain lions and wolves had been eradicated within Yellowstone National Park and had not returned. Gradually though, the cougars found their way back and a research project was begun by Toni Ruth with the Hornocker Wildlife Institute. She found their numbers steadily growing in the late 1990’s. Wolves, as we all know, needed reintroduction to make a comeback. 

Now however, both species have healthy populations and they are naturally expanding into whatever habitat may be available. The cougar that was killed in 2000 may have come all the way from Yellowstone Park.
Between January 2001 and June 2010 in just one stretch, 2,272 animals representing 49 different species of mammals, birds and reptiles were recorded as road kill. How many more we don’t know, but the verified count is high as it is. 
The place where the cougar was killed is another factor in the accident. For the most part, dispersing or migrating animals do not move across the landscape at random. They tend to stay within habitats that may offer them food or shelter or security. They tend to travel in what have come to be known as "wildlife corridors." Corridors are places where animals are known to travel, or where they are likely to travel based upon what we know of their behavior.

Bozeman Pass is such a place. It is an area with good wildlife habitat on both sides of the highway barrier. It is an important crossing point for animals moving north or south. It will become even more important as the climate warms and animals of many species begin searching for better habitats than the places they used to live—as those places become uninhabitable.

Between January 2001 and June 2010, 2,272 animals representing 49 different species of mammals, birds and reptiles were recorded as road kill on Bozeman Pass alone. How many more we don’t know, but the verified count is high as it is. Various studies show that visible roadkill is 50 percent or less of actual animals killed; many wander off a ways before dying, or get crippled and die eventually.

Seasonally, most ungulates were killed in the autumn months of October and November, followed by a smaller peak in the summer months of June and July.
The decade-long analysis of roadkill data by the Craighead Institute served as a wake-up call for the problems that Interstate 90 posed for connectivity.  With population growth and rising numbers of visitors coming to Yellowstone, the last eight years have made the interstate even more formidable.
The decade-long analysis of roadkill data by the Craighead Institute served as a wake-up call for the problems that Interstate 90 posed for connectivity. With population growth and rising numbers of visitors coming to Yellowstone, the last eight years have made the interstate even more formidable.
Places like Bozeman Pass are areas where we need to provide safe crossings for wildlife so that they can live normally and so that they can adjust to climate change, being able to move from, say, one stretch of public lands (the Gallatin and Absaroka ranges) to other sweeps (the Bridgers, Bangtails and Crazies).

We also need to protect habitat on both sides of the highways by establishing conservation easements on private lands and protecting public lands from excessive development and recreation through agency processes like the current Custer-Gallatin National Forest Plan Revision. Currently, the U.S. Forest Service, based on our analysis, has not proposed adequate measures to protect and maintain these corridors.

More on that to come. In the meantime, though, as you are cruising through the Greater Yellowstone Ecosystem, try to imagine all of the animals that have crossed the road in light or darkness. Their habitat extends across the asphalt and gravel. They see the world different than we do and their survival depends on it.

EDITOR’S NOTE: This article will be part of a series of articles that look at wildlife connectivity, ecology, human population growth,  and climate change from a scientist’s perspective and where those issues intersect.  
Lance Craighead
About Lance Craighead

Frank Lance Craighead, PhD—he goes by "Lance"— is son of the late Frank Craighead and nephew of John Craighead—twin brothers who were involved with pioneering research on grizzly bears in the Greater Yellowstone Ecosystem and birds of prey. Their work was featured by National Geographic. Lance and his wife, April, are chief scientists with the Bozeman, Montana-based Craighead Institute, founded by Frank Craighead.
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