The Wyoming Game and Fish Department is proposing to officially designate and protect two western-Wyoming ungulate migration corridors, one of which would build on existing federal protections of the nationally renown “Path of the Pronghorn.” (John Fandek)

The Wyoming Game and Fish Department is proposing to officially designate and protect two western-Wyoming ungulate migration corridors.

One designation would build on existing federal protections of the nationally renown “Path of the Pronghorn” — guarding for the first time a stretch of the route that extends beyond the national forest. The second would create accommodations for a more recently identified mule deer route through the Wyoming Range.

Conservationists support the designations but they fear that aggressive federal leasing for oil and gas development jeopardizes the routes and the deer and pronghorn populations that need them. Wyoming has to step up to ensure that lease stipulations are sufficient to protect the migration corridors, the conservation groups contend.

The department is assembling public comment from a series of meetings at which it presented its case for the Sublette Pronghorn and Wyoming Range Mule Deer paths. The goal, according to department personnel, is to add the corridors to the department’s catalog of designated vital habitat, thus enabling the Game and Fish Commission — an appointed panel of citizens that oversees the agency — to better fulfill its charge of protecting the state’s wildlife.

Already the commission and agency designate winter range and other sensitive habitat for protection. But it’s critical, Brandon Scurlock, regional wildlife coordinator with the Game and Fish in Pinedale says, that the routes between seasonal habitat be guarded as well, helping the agency act and react to changing circumstances.

The routes, mapped using information gleaned from GPS collars fitted on annually migrating wildlife, outline high, medium and low-use corridors. They also identify critical “stopover” areas where the wildlife lingers along the seasonal treks as an important part of the designations.

Data from GPS collars fitted to migrating pronghorn reveal the width of the migration route and how long pronghorn spent in various locations. (Wyoming Game and Fish)

The mapped pronghorn path stretches, sometimes intermittently, 180 miles from Grand Teton National Park, south and east through the Bridger-Teton National Forest, along Bureau of Land Management and private property through the upper Green River basin and Red Desert to wintering areas near Rock Springs.

The proposed Wyoming Range Mule Deer Corridor wends a braided way more than 130 miles from the Hoback Rim above Bondurant to south of Kemmerer. A significant portion crosses the Wyoming and Salt River ranges in the Bridger-Teton, but it involves BLM and private land as well.

“The commission will make the ultimate decision whether they make it an official corridor or not,” Scurlock said. That could come later this spring.

Meantime, he said the GPS data from the collared animals is convincing. “You can say you don’t like it,” he said of the corridors and their locations, “but this is what the animals did.”

Completing the job

In 1985 two biologists in the southern part of Wyoming’s Green River basin caught several pronghorn antelope, and fitted each with a colored, vinyl neckband, according to Wild Migrations; Atlas of Wyoming’s Ungulates. There were no transmitters attached to send off radio waves, no miniaturized computers to correspond with global positioning satellites.

This is how the neck bands worked: “The next summer, two adult female pronghorn wearing white neck bands were observed in Jackson Hole, indisputably linking the valley to the winter range, 150 miles to the south,” the migration atlas reads.

But how did they get from the basin to Jackson Hole? Researcher Hall Sawyer and associates found the next piece of the puzzle and put it in place. He captured pronghorn and fitted them with transmitters. Trackers had to spend hours in the hills with receivers pinpointing locations of each transmitter.

The result was a series of points that delineated a route from Grand Teton National Park up the Gros Ventre River drainage, over the divide between the Snake River and Green River drainages, and on south. That’s where several hundred pronghorn went every fall; every spring they trekked back the other way.

Steve Cain from Grand Teton National Park provided more information with the next iteration of technology — GPS collars. Linking to satellites, they revealed the width of the path and how long pronghorn spent in various locations. With this information and advocacy from fellow researcher Joel Berger, the Bridger-Teton National Forest acted to largely preclude human interference along the route by amending its management plan.

Carole “Kniffy” Hamilton, supervisor of the Bridger-Teton, in 2008, designated the Path of the Pronghorn across about 47,000 acres. It became the first federally recognized wildlife migration route in the country.

“But it didn’t connect with winter ranges farther south,” Scurlock said. The protected route on the national forest stopped far short of the pronghorns’ destinations.

In only four years researchers captured and collared 126 mule deer and tracked 505 migration sequences, revealing the migration route mapped here. (Wyoming Game and Fish)

After crossing some 40 or so miles of the Bridger-Teton on their way south each fall, pronghorn leave Hamilton’s designated corridor and begin to traverse a patchwork of private and public land. The pronghorn don’t stop until reaching wintering grounds, largely on BLM land, another 80 or 90 miles or so beyond.

It’s this as yet unprotected stretch that Game and Fish aims to guard by designating the entire route.

“It should be noted that the Forest Service by itself cannot guarantee continued successful migration of this herd over the entire migration route,” Hamilton wrote when designating the corridor on the national forest. “There are numerous factors beyond Forest Service control such as activities on lands under other jurisdictions within the migration route.”

Since 1985 the landscape along the Path of the Pronghorn has changed dramatically. In the 1990s, near the southern terminus, an energy company developed the Jonah Field across some 21,000 acres, extracting and exporting natural gas. Other companies developed the Pinedale Anticline along the path and Jonah Energy recently received approval to drill the Normally Pressured Lance Field — that development will take place on the migration route.

Private lands in the area have been subdivided and developed with homes.

Federal land managers tempered their approval of the energy projects with various requirements. In some cases, drilling is allowed only during certain times of the year. The BLM controls the density of development, and its pace. Other measures — like conservation easements placed on private land and antelope bridges constructed over U.S. Highway 191 — seek to preserve or enhance the path. Conservation groups and Game and Fish remove unused fences and modify some of those that are necessary. The agency undertakes efforts to curtail invasive species and improve habitat in other ways.

Now, using data collected between 2005 and 2017, Game and Fish is ready to extend the protected pronghorn path to make it stretch, with some discontinuity at its southern end, almost 180 miles. Researchers from a variety of agencies including Grand Teton National Park followed 111 pronghorn to create the corridor outline. Researchers tracked 230 migrations before taking their findings on the road to show the public.

An iconic herd

Scant miles to the west of the pronghorn route Game and Fish, again relying heavily on partners including UW’s Wyoming Migration Initiative, has sketched the Wyoming Range Mule Deer Migration Corridor. In only four years researchers captured and collared 126 mule deer and tracked 505 migration sequences.

The web of mule deer routes laces two mountain ranges between Afton, Kemmerer, Big Piney and the Hoback Rim. Much of the routes traverse national forest and BLM property. Wide-ranging oil and gas development covers nearby areas and has been underway “for quite a while — 100 years,” Scurlock said. But Congress saved the core of the corridor.

Mule deer does and fawns stage on winter range before beginning the spring migration north through the Wyoming Range. Wyoming researchers say the deer “surf” a wave of spring green-up on migrations routes, which are now considered habitat as much as avenues for travel. (Samantha Dwinnell)

In 2009 Washington, D.C. lawmakers cemented the legacy of Wyoming Sen. Craig Thomas, who died before accomplishing his vision, to protect 1.2 million acres of national forest land vital to area mule deer. Sen. John Barrasso who replaced him, carried the legislation, which prohibits new oil and gas leasing, to completion.

Still, portions of the route remain under threat, though perhaps not as much a threat as that faced by the pronghorn, Scurlock said.

Wyoming’s fourth and fifth corridors

The two proposals would augment the state’s three existing designated wildlife corridors, bringing the total to five. They’ve been mapped by Game and Fish personnel and independent biologists, scientists and students, including members of the Wyoming Migration Initiative at the University of Wyoming.

In southern Wyoming, the Baggs Mule Deer Migration Corridor stretches some 60 miles from just south of Rawlins to the Colorado border.

Wildlife scientists identified it after collaring 118 mule deer and recording 128 migrations. It crosses BLM, private and national forest lands and along the western edge of the Sierra Madre. Deer likely follow it into the Centennial State.

The Platte Valley Mule Deer Migration Corridor includes several routes east and south of Rawlins. The longest continuous stretch runs approximately 40 miles along the western edge of the Medicine Bow Mountains. Biologists tracked 40 mule deer making 128 migrations to map this route.

The Sublette Mule Deer Migration Route outlines the avenue followed by mule deer on what’s popularly known as the Red Desert-to-Hoback route that runs more than 140 miles from Hoback Junction south of Jackson to Interstate 80 east of Rock Springs. One hundred and thirty-one mule deer making 319 migration sequences enabled cartographers to establish the boundaries of that vital habitat. It’s the longest mule deer migration ever recorded and takes animals two months — one way — to accomplish.

Biologists used GPS tracking collars to discover America’s longest mule deer migration from the Red Desert to the Hoback Mountains in Wyoming. (photo by – Joe Riis)

Five hundred deer begin their travels in the Red Desert and are joined by another 4,000 or so along the way.

Researchers used similar tracking techniques to map the proposed new corridors. Wildlife is first captured, then fitted with collars that transmit a location to a satellite every few hours. Compiled data shows where the animals go, how long and where they linger and where they hurry along — like through developed areas. The information reveals where the deer and the antelope cross highways and how many fences they encounter along the way.

The agency defines long-distance migrations as those that encompass a route 50 miles or longer, Scurlock said.

OK, a corridor — now what?

Once a corridor is designated, Game and Fish commits to its preservation by advocating for “no significant declines in species abundance and habitat function,” Scurlock said. In most areas that means communicating the agency’s priorities to the federal government as it leases lands for oil and gas exploration and development. Few Wyoming counties  impose zoning restrictions on private-land development in migration corridors.

Armed with delineated migration corridors, Game and Fish engages with the BLM on a case-by case basis as projects emerge, seeking to limit impacts. In recent months under the Trump administration’s policy of energy dominance, Game and Fish has recommended, and the BLM has agreed, to put off leasing parcels that lie wholly within migration corridors.

When as little as 10 percent of a parcel lies outside a corridor, however, and there is suitable land there to drill a well, Game and Fish will ask BLM, the regulating agency, to attach a notice to the leases. The notices say operators “will be required to work with the BLM and Wyoming Game and Fish Department to take reasonable measures … to avoid and minimize impacts to maintain big game migration corridor functionality.” They also “encourage” the use of master development plans should energy companies strike a significant find.

“We’re not trying to limit oil and gas development,” Scurlock said, “but maintain [corridor] functionality.”

Such notices are toothless guardians of the wildlife resource in the eyes of some conservationists. Joshua Coursey, president of the Green River based Muley Fanatic Foundation, would prefer all leases within designated migration corridors require “no surface occupancy.” Such a legally enforceable stipulation – not just a notice – would prohibit surface-disturbing activities within the corridors, a prohibition that’s far stronger than the notices.

“That’s a short and sweet answer,” Coursey said. “Within those corridors, I think NSO is the best for the wildlife and resources. We would like to see the Game and Fish be the author of the stipulations.”

No-surface-occupancy restrictions would be “making sure the playbook is clear and everybody understands it,” he said. “I think it’s the unknown that’s created the frustration.”

But he supports the Game and Fish’s efforts. “I’m glad to see the conversation is being had and the department is going out soliciting feedback,” he told WyoFile. “I think it bodes well.”

Regarding the 10 percent rule “at the end of the day, things get done through compromise,” Coursey said.

Gov. Mark Gordon said in a statement he believes existing protections are adequate to protect the migration routes. WyoFile did not receive a response to a request for comment from the Petroleum Association of Wyoming.

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Others are more skeptical. Game and Fish claims to have used best available science in plotting the routes, said Linda Baker, a conservationist with the Upper Green River Alliance. Yet, “they are unable to cite any scientific studies or analysis that can justify the 90 percent rule,” she wrote WyoFile in a letter.

Development on the border of a migration route could be too close, she wrote. “The indirect impacts to wildlife populations from the noise, traffic, and year-round habitat disturbance on a lease extend for a mile or more,” she wrote. Those indirect impacts are “just as disruptive to wildlife as direct impacts.”

Approaching threats on a case-by-case basis “contradicts a range-wide management strategy long utilized by both the WGFD and BLM,” Baker wrote.

Conservationists are troubled by the pace of the leasing as well. Last week the BLM auctioned rights to drill on approximately 765,000 acres in Wyoming, an area critics say is the largest single sale under the administration outside of Alaska.

“Wyoming leaders must stand up to the feds and ensure that leasing does not occur in these places,” the Wyoming Wilderness Association’s Shaleas Harrison wrote in a statement. “Once they are compromised, we cannot get them back.”

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Angus M. Thuermer Jr.

Angus M. Thuermer Jr. is the natural resources reporter for WyoFile. He is a veteran Wyoming reporter and editor with more than 35 years experience in Wyoming. Contact him at or (307)...

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  1. We have suggested a workable solution to this problem. Please see our February 9th post on our Facebook page, Wyoming Sportsmen for Federal Lands.

  2. Excellent article, summary and update on the current issues involving key migration paths. Thank you, Angus & Wyofile.