America’s Wildlife Corridors Are in Danger

Most of them are still a mystery to science, and the ones we know about have big problems.

Joe Riis

Right about now a few thousand mule deer are moving south through the grass valleys near the bottom of Wyoming’s Wind River Range. They summered in the high alpines near Yellowstone National Park, and as winter comes they’ve traveled 100 miles south, through private and public land, with still 50 miles more to go, across rivers, deserted two-lane highways and busy freeways, noisy natural gas fields, and barbed wire fences. Many of them are bound for a desolate sagebrush basin called the Red Desert, where they will hit a wall in the form of the four-lane Interstate 80. It is the longest land mammal migration in the lower-48 U.S. states, discovered only two years ago.

Since researchers found it, the Red Desert to Hoback mule deer corridor has made the study of land migration suddenly sexy—“very sexy,” Steve Kilpatrick, a field scientist working with the Wyoming Wildlife Federation, told me. Corridor ecology has been around a long time, but only recently has it gained wide interest. This is partly thanks to Hall Sawyer, the research biologist who found the route, and who together with the Wyoming Migration Initiative published a revolutionary study on the path, which included a stunning video shot by a National Geographic photographer. But it’s also owed to what the corridor offered conservationists. “This migration route has been going on for hundreds years,” Kilpatrick said, “and now all at once we can define it.” But that doesn’t mean it’s not in danger.

There are 5,000 mule deer that make the 300 miles round trip each year. Researchers had mapped their path with GPS collars, then detailed their route at such granular levels, and in astonishing clarity. Anyone reading the report can see, for instance, that  in their current movements this month they must cross eight fences, six of which are made of dangerous woven wire. It’s been two years since Sawyer discovered the path accidentally. He had collared deer he believed spent the year in the Red Desert, a high altitude steppe at the southern end of Wyoming. Two years later what he and the Wyoming Migration Initiative accomplished has become a conservation paradigm. If any migration corridor has a chance to be redeemed it is this one, but the barriers to protect it are many, and not so easily solved.

A month ago, the Red Desert mule deer herd passed east of the town of Pinedale, Wyoming, foraging as they moved. Mule deer are slightly larger than the more common white-tailed deer, and they’re most easily identified by their comically large ears, which, as their name suggests, resemble a mule’s. They were once the most common big-game animal in the West, but their numbers have plunged 20 percent in the past 25 years. As they passed near Pinedale, they moved through land the study listed as priority number one for protection. Here, the problem is a bottleneck, created by the Wind River Range, Fremont Lake, and private land with an impassable fence, which together forced thousands of deer into an area the mere width of a football field. Mule deer, like many ungulates in the U.S., pass migration routes down from generation to generation, so it’s possible that if a route becomes blocked the deer will lose it forever. Deer don’t have to migrate, and not all deer in a herd do migrate. They could survive without the corridor. But only through migration can ungulates sustain the populations they’re used to, and that carnivores up the food chain depend upon. If the Red Desert mule deer stopped moving north to the peripheries of Yellowstone, the cougars, wolves, grizzlies, coyotes, and the bald eagles and hawks that scavenge their kills, would all go without that protein.

Wyoming Migration Initiative

As luck would have it—but no doubt because of the study’s publicity—a piece of property alongside the bottleneck went on the market. The Conservation Fund, an environmental non-profit, bought the 364-acre parcel in 2015 for $1.7 million. This November it was transferred to the Wyoming Game and Fish Commision, which will manage and preserve the land in perpetuity. In the world of corridor ecology, this qualified as a miracle. And it only happened because the Wyoming Migration Initiative study won the collective interest of groups like the Conservation Fund, which purchases land, federal and state agencies, wildlife policy organizations like the Wilderness Society, the Wyoming Outdoor Council, and wildlife groups with strong hunter support, like the Wyoming Wildlife Federation. These groups (14 in all) spent two days in a conference room talking through each mile of the corridor. They made a list of threats to the path and have set about to resolve each, the worst of which was the bottleneck. Next up were roads and oil pads.

One of the major discoveries as of late is that deer migration is less of a sprint, more of a meander—“like a pub crawl,” Julia Stuble, the public lands advocate for the Wyoming Outdoor Council, told me. As mule deer move north for the summer they follow the “green wave” of blooming vegetation, and as the herd moves south in the fall the deer pick over the last remaining greens, hoarding life-saving calories. The danger is that in some areas along the corridor there are huge natural gas extraction sites and the constant activity around them make the deer skittish. The deer move faster around oil pads, and when that happens they miss out on vital calories. As researchers better understand deer stopover territories it has become almost as important to protect these meadows as it is to save the central corridor. Even something as small as limiting truck trips to well pads from eight a day, down to three, has proven helpful. Already, one of the country’s largest natural gas fields lies near the mule deer’s path, and much of the land along the corridor’s southern edge is in Bureau of Land Management (BLM) controlled territory, where oil well pads are in operation, and could become more common.

Right now, Stuble told me, the BLM office in Rock Springs, the agency that oversees energy extraction in the area, is rewriting land use policy that will dictate how companies can drill for the next 15 years. “We operate in a highly conservative state,” Stuble said, “where the economy is based off mineral extraction from the land. But it’s important to recognize that while we drill or mine in some places, it doesn’t have to be everywhere.”

Along the migration corridor the deer will cross many roads, and the issue with roads is pretty straightforward, as anyone who’s seen bloated roadkill along a highway can attest. The solution, however, is expensive. Along the Red Desert to Hoback trail the mule deer will cross major highways like Wyoming Highway 28, Wyoming Highway 352, and U.S. Route 191, a scenic two-lane road that cuts through the green timber forests of Grand Teton National Park, up to Yellowstone. In 2011, the Wyoming Department of Transportation built wildlife over-and underpasses along U.S. Route 191 near Pinedale. These are like bike paths that allow wildlife to safely cross a busy road, and eight of them cost Wyoming $9.7 million. Each year they help thousands of pronghorn cross the highway, but they’re too far south to aid the Red Desert mule deer. Luckily for the animals, a 130-pound deer does a decent amount of damage to a car at 60 miles per hour, and because so many cars hit mule deer along U.S. Route 191, Wyoming is considering more wildlife overpasses.

Of all the barriers facing deer, and all ungulate migration in the U.S., the easiest to resolve should be fences. A few wires stretched along posts can snap a deer’s leg if it’s caught while jumping, or tangle in their horns as they slide underneath. It’s a brutal death. A snagged deer typically starves to death or fights itself into exhaustion. One study from the University of Utah tracked 600 miles of fence in Colorado and Utah and found that for every 2.5 miles one ungulate tangled itslef in the wire each year. These fences are everywhere. Just along the Red Desert to Hoback corridor there are more than 100 fences, one of which surrounds the Rolling Thunder Ranch, owned by Tim Delaney.

A few weeks ago Delaney stood on his 7,600 acres of land and watched hundreds of deer bound over his fences. The barbed wires keep his cattle in, but Delaney was also keenly aware of the problems they caused the deer. Obviously, before the study came out, Delaney knew deer liked his property, but he had no idea it was part of a corridor for thousands. Armed with the corridor study, last year the Wyoming Wildlife Federation reached out to Delaney and said they’d found funding to replace his fence. So far, five miles of fencing on Delany’s ranch has been lowered to 40 inches so deer can easily clear it as they  jump, and the bottom wires raised to more than one foot, so young deer can slip below. “We’re in their country, right,” Delaney told me, meaning the deer’s country. “This is an opportunity where we can significantly lessen our impact on their turf, and it gives us the upgrade for our fences.”

Everyone wins with fence replacement, and that’s all fine and good, but this requires willing participation on behalf of private landowners, and not everyone is as receptive as Delany. Replacing fences is also expensive. It has cost about $25,000 a mile to replace Delaney’s fence. And although his required a bit more work than average, a similar project in the same Wyoming county to replace 45 miles of fence is expected to run more than $600,000. These expenses have been raised by the collective of nonprofits working to save the corridor, which most likely only happened because of all the attention the Red Desert to Hoback trail received.

Now, consider the great gains made in the past two years for the mule deer, and consider that optimistic estimates of the challenges ahead (if progress continues as it has) will still take years, perhaps a decade to resolve. Of course, there are hundreds of other migration corridors, some known, many more still in need of mapping, all across the West. Realize that deer, elk, moose, pronghorn, and antelope all depend on the ability to move north and south as seasons change, and that humans are still procreating and building roads and homes. Migration for ungulates will only become harder. What will happen in the future, Hall Sawyer, the biologist who discovered the Red Desert to Hoback corridor, told me, will be similar to what happens after a gory car crash: triage.

“The ideal is you throw that map out and say, ‘Hey let’s try and protect all this,’” Sawyer said. “But in private landscapes and multiple-use land that’s not really an option.”

Biologists hope to map more of these corridors in the same way they have the Red Desert to Hoback path, and surely some will be saved, thanks to the breakthroughs made by Sawyer and the Wyoming Migration Initiative. But some will fade out. It’s likely many herds, never fully understood, will vanish. By the end of December, the mule deer will finish their journey and arrive in the Red Desert, where they will spend the winter surviving on what little vegetation they can scrounge beneath the snowpack. This is a relatively new end for the herd, because here they’ll run up against the four lanes of Interstate 80, completed in 1986, built before anyone knew it would forever alter the trail of the mule deer.