Wyoming Looks to Designate Famed Path of the Pronghorn

by Alex Hargrave 

Wyoming wildlife managers could soon protect the longest terrestrial migration route in the Lower 48 states, a path stretching roughly 200 miles from the Grand Tetons to the Green River Valley.

The state’s largest American antelope herd travels the famed Path of the Pronghorn each year to winter at lower elevations and avoid the harsh conditions in the Tetons. A recently released biological risk and opportunity assessment highlights the obstacles faced by the thousands of pronghorn as they travel the route. 

More formally known as the Sublette Antelope Migration Corridor, the Path of the Pronghorn rose to prominence in the conservation world after its federal designation led to effective conservation measures such as wildlife-friendly fencing and oil and gas lease deferments. While the terms pronghorn and antelope are often colloquially used interchangeably, they are members of different families. Pronghorn are unique to North America and are considered the fastest land mammals on the continent, reaching top speeds of nearly 60 mph, enabling the animals to travel such long distances. 

The corridor is currently being recommended for designation at the state level by the Wyoming Game and Fish Department. Formal state designation would unlock additional funding opportunities for conservation projects on both public and private lands, according to the agency. A portion of the route was federally designated as a migration corridor in a 2006 Bridger-Teton National Forest Plan amendment, which directs the management of federal lands within the corridor to protect winter and summer migration.

A 2020 executive order issued by Wyoming Governor Mark Gordon added to past migration corridor designation policy and dubbed the governor the ultimate decision-maker instead of Game and Fish. 

According to the order, the process for designation starts when the Game and Fish Department identifies a corridor, and the agency then releases a biological risk assessment in consultation with federal, state and county partners and notifies private landowners. From there, the commission reviews the assessment, opens a public comment period and subsequently votes on whether to designate the corridor.

With the final authority, the governor will determine whether to designate a corridor and, if so, convene an area working group with leaders from all affected counties or tribes who meet publicly and present management recommendations to the governor. 

If Sublette Antelope Migration Corridor designation passes the commission, it will be the first under the new executive order. Three mule deer migration corridors have already been designated by the state.

Commissioners will vote on the measure at their July meeting in Evanston, Wyoming. In the meantime, the department is accepting public comments through May 2. 

The commission’s upcoming vote is a long time coming for wildlife advocates that have followed the issue. It’s become more relevant for proponents since the winter of 2022-23, when the pronghorn herd’s population fell to a 30-year low after severe weather conditions and disease caused widespread mortality. Roughly 90 percent of the pronghorn that migrate to the northernmost segments in and near Grand Teton National Park died.

“This population took a huge hit, especially in the north of the herd’s range,” Meghan Riley, wildlife program manager with the Wyoming Outdoor Council, said in a statement after Game and Fish released its assessment in March. “Recovery is slow going and precarious, given existing and anticipated threats to corridor functionality.”

Nat Peterson, policy director with the Wyoming Wildlife Federation, told Mountain Journal in an interview that migration corridors are “the lifeblood” of certain ungulate herds who inhabit the state’s open spaces and undeveloped land. His organization, which advocates for conservation on behalf of hunters and anglers, was involved in drafting the executive order and has supported designation of what he says is one of the most well-known wildlife migration corridors in the country.

“We want to keep it that way,” Peterson said. “We’re not saying that development, necessarily, is a bad thing, but ideally it’s located outside of critical wildlife habitat.”

When the commission voted in March 2024 to accept the department’s recommendation to identify the corridor, officials noted that 90 percent of public comments were supportive of the designation, according to meeting minutes. 

Over the years, designation has seen pushback from industry and some local officials concerned about how the designation could impact local production activity. After the significant winter mortalities two years ago, some questioned whether the designation was merely a reaction to the unprecedented event. 

Pete Obermueller, President of the Petroleum Association of Wyoming, said in mid-April that the group has helped develop the process to identify and designate migration corridors. 

“While not perfect, we are satisfied with the Executive Order that created the process,” Obermueller said in a statement. “The Sublette Antelope Corridor is proceeding through that process, and we will comment on it at the appropriate time.”

Jim Magagna, executive vice president of the Wyoming Stockgrowers Association, an advocacy group for the state’s ranchers, said the organization is generally supportive of protecting the migration corridor. Still, he has concerns that while the state would not necessarily seek to reduce or ban livestock grazing on lands within the designated corridor, it could enable federal agencies to make that move in the future. 

“When you put restrictions on an area or a name on an area, it adds impetus to some of our real opponents out there — more radical environmental groups that don’t support livestock grazing — another tool to their arguments for why grazing should be reduced or eliminated in an area,” he said in an interview.

The Sublette pronghorn herd is one of the most studied ungulate herds in the world, Game and Fish notes in its biological assessment. That means managers can consult a wealth of data in their decision making. 

The near 200-mile migration corridor crosses several state, private and federal land boundaries, including Bureau of Land Management, U.S. Forest Service, U.S. Fish and Wildlife Service and National Park Service managed lands. Pronghorn migrations tend to be more spread out than those of mule deer, the assessment notes. 

The pronghorn spend their summers among the sagebrush at the base of the Teton Range near Jackson and migrate south, past Pinedale, where they disburse into the Upper Green River Basin, the Red Desert and as far south as Interstate 80 where it traverses Green River and Rock Springs in southwest Wyoming.

As part of its assessment, Game and Fish identified 13 corridor bottlenecks, which are defined in the governor’s executive order as areas where animals are significantly restricted either physically or behaviorally by landscape features or development. 

In these sections, the ungulates, tracked by GPS collars, move through a geographically constrained space. Identified bottlenecks are associated with wildlife and river crossings, unsuitable forested habitat, constricting topography and human disturbance. These areas are a particular target for conservation efforts because they could potentially sever the corridor, the assessment notes. 

Bottlenecks are one symptom of habitat fragmentation, which the assessment identifies as the most significant threat to the corridor. It says higher density residential development in rural areas that overlap with wildlife habitat, along with energy and mineral extraction, have the most significant habitat impacts.

The effects of oil and gas activity and extraction for more novel gases, such as helium, can be minimized by developing outside of high-use areas, stopover habitats and bottlenecks, the report notes. 

The assessment evoked the deadly winter of 2022-2023 due to extreme winter weather conditions and an outbreak of M. bovis bacterial disease. Its authors report that the unprecedented die-off highlighted the importance of the animals’ winter range and their ability to get to the destination; GPS collar data showed that pronghorn who traveled farther south had better survival rates than those who camped out farther north.  

A recently released University of Wyoming study published in the journal Current Biology found that pronghorn struggled to navigate tens of miles of fence and road barriers along the migration corridor during that winter. The extreme weather that made it difficult for the species to find sustenance, combined with the difficult-to-pass barriers, led to a breakdown in habitat connectivity, researchers noted.

“Seeing the movements of these pronghorn paints such a clear picture of a struggle to escape,” Ellen Aikens, lead author of the paper and assistant professor at the University of Wyoming School of Computing and Haub School of Environment and Natural Resources, said in a news release. “It was truly sobering to see how some pronghorn got hung up on fences while others traced along Interstate 80 for miles.” 

Other impacts to habitat noted in the assessment include invasive vegetation, recreation and feral horses.

Magagna said that one of his concerns with the designation is its breadth. The middle portion of the corridor that stretches from Hoback Junction, tracks east of the Green River and into the Red Desert, he noted, has several bottlenecks identified based on subdivision and energy development. A portion on the west side of the Green River and two factions farthest east do not face those same challenges and, in his view, don’t warrant designation. 

“It’s too broad,” he said. “It brings in several hundred thousand acres that really don’t fit with the Sublette migration corridor that’s been the focus of attention.”

A state designation would not impact activity on private lands within the bounds of the corridor, the executive order clarifies. Twenty percent of private land acreage within the corridor is protected by conservation easements, which are voluntary contracts between a landowner and a conservation organization or land trust that ensure the land will not be subdivided in order to protect wildlife habitat. 

Magagna said that the stockgrowers organization, like several other stakeholder groups in the state, was involved in drafting the new executive order and is generally pleased with its outcome, namely that activities on private land will not be restricted.

Designation of the corridor would also limit certain human-use activities within the corridor, which would be managed to maintain habitat and minimize future disturbance. The state will still allow existing permits and activities.

In sections of the corridor classified as bottlenecks, the executive order stipulates that new impacts to habitat or seasonal human presence will not be permitted. 

“Locating surface disturbance outside of high-use areas, stopover habitats, and bottlenecks allows for multiple uses of the landscape while ensuring the long-term conservation of the Sublette Antelope Corridor,” the assessment says. “Designating this Corridor empowers companies and local governments to proactively use science and data to make decisions that accommodate a variety of uses on the landscape while protecting the most sensitive areas of the Corridor.”

Per the order, designation would direct the Wyoming Department of Transportation to work with Game and Fish and other state agencies to mitigate wildlife-vehicle collisions and facilitate big game movement within the corridor by installing wildlife crossings and other practical infrastructure. 

“Designation places more of an emphasis on the corridor,” Peterson said. “Game and Fish will release maps about where the corridor is. It makes it easier to conserve from a private landowner perspective and a state agency perspective.”