Sublette pronghorn migration draft report is out

Cali O'Hare file photo

G&F to recommend ‘pursuit’ of official designation

SUBLETTE COUNTY – Wyoming’s time-consuming process to analyze years of migration data and evaluate threats before seeking its formal designation of the ancient Sublette antelope migration corridor is now poised to involve the public.

Wyoming and Sublette County hold some of the most important and longest stretches of prehistoric ungulate migration corridors. In fall when weather threatens, bunches of pronghorn antelope does, fawns and bucks gather into larger groups and fill up on forage, as they did recently in a private hayfield in Hoback Basin.

Incidental to protecting their migration corridor but creating a sense of urgency, many pronghorn died last winter from starvation and disease in Sublette County and across the state, concerning Wyoming Game and Fish biologists and other stakeholders.

This week on Tuesday, Game and Fish’s biologist Ashleigh Rhea, with the Pinedale Anticline Project Office (PAPO), told board members the Sublette pronghorn herd lost an estimated 75 percent of its population.

Executive order

Recently, Wyoming Game and Fish Director Brian Nesvik hinted at the state wildlife agency’s next step in identifying parameters for the long-awaited pronghorn corridor designation, following the U.S. Forest Service official “Path of the Pronghorn.”

The formal designation process for the Sublette Mule Deer Herd’s Red Desert to Hoback migration route was completed several years ago.

Now, the official pronghorn corridor designation process is outlined in Gov. Mark Gordon’s Migration Corridor Executive Order, which does not apply to private lands and does not affect existing energy developments on public lands.

The first step was drafting the “threat evaluation” of risks and obstacles to the pronghorns’ continued use of the 368-mile roundtrip corridor from Rock Springs through Hoback Basin to Jackson Hole. The draft reviewed 20 years of data gathered from 2002 to 2022 in Sublette, Fremont, Lincoln, Sweetwater and Teton counties on private, state and federal lands.

This “unprecedented amount of GPS data” came from more than 415 individual animals traveling both ways each year on their historic migration routes, mapping their stopovers, bottlenecks and low, medium and high use habitats, said Game and Fish’s Doug Brimeyer.

GPS collar studies to delineate the pronghorn corridor were in Kemmerer, Grand Teton National Park, Pinedale Anticline, Jack Morrow Hills, I-80, Sweetwater Solar and from 2020 to 2024, in areas not previously studied.

Detailed maps broken into segments accompany the new draft threat and risk assessment report open for public comment through Jan. 5, 2024.


The draft list of existing and potential threats in 10 years starts with “subdivision or suburban sprawl” as the top concern.

“One of the most pressing (threats) is habitat loss associated with the expansion of suburban development and general expansion of the human population into native habitats,” the draft states. “… (A)ssociated disturbance from roads, fences, pets and humans have already affected the functionality of the corridor in some areas, and demand for more development continues to be a pressing concern. Recently, the influx of people relocating to western Wyoming has greatly increased, likely fueled by the COVID-19 pandemic and the increased ability for employees to telework away from urban centers.

“As of 2021, the total population of Sublette County has increased 78 percent since 1990 and 46 percent since (U.S. Census Bureau 2021). Demand for additional residential development and changes to county zoning to accommodate this demand has occurred throughout the corridor.”

Energy development is “another significant threat,” the draft says.

Fence impacts (all fence conditions or not wildlife-friendly design) are another existing and future threat, as are improved road impacts, oil or gas wells or permits to drill, solar projects, transmission lines, compressor stations or pipelines, mineral mining, other energy or resource extraction, closed canopy or late succession-reducing herbaceous forage and habitat impacts from wild horses.

Wind development is not an existing threat but a future threat, as is wildfire threat due to cheatgrass invasion of sagebrush ecosystems.

Human recreation, whether motorized or non-motorized, is the only activity not considered a current or future threat – yet.

“Disturbance from increased recreation such as off-road vehicles, mountain biking and antler hunting during critical times of the year may impact the functionality of the migration corridor for pronghorn, but there is little science or data at this time on these disturbances,” the draft says.


Existing and future migration corridor “protections” include federal wildernesses, wilderness study areas, areas of critical environmental concern, no surface occupancy or conditional seasonal land-lease plans, conservation easements, projects in development to mitigate threats and “other federally designated migration corridor, Path of the Pronghorn.”

While not required, private landowners voluntarily reduce negative impacts to wildlife, the draft report says.

“Private landowners have contributed significantly to the function of the corridor by voluntarily placing conservation easements on tens of thousands of acres within the corridor. Typically these deed restrictions maintain significant areas of open space indefinitely, even if the parcel is sold in the future. Also, landowners have voluntarily participated in cheatgrass and other noxious weed management efforts, implemented habitat enhancements to improve forage quality and modified hundreds of miles of wildlife friendly fence.

“Specific county zoning protections for private land that overlaps the proposed corridor are not expected to be current or future protections. The USDA’s new Grassland Conservation Reserve Program (G-CRP) is not currently – but is forecast to become – a corridor protection program.”


In closing, the draft reports says, “The existing trend of suburban expansion and demand for renewable energy resources are the most concerning threats to the functionality of the corridor. In addition, the recent population level impact sustained during the 2022-23 winter makes these threats more influential. The protections identified through land ownership and other vital wildlife habitats are not sufficient to mitigate the impacts of the threats. For these reasons, the Department recommends pursuing the designation process as outlined in the Wyoming Executive Order 2020-1.”

Learn more

Wyoming Game and Fish will host three public meetings at its regional offices, the first in Pinedale on Thursday, Nov. 16, at 6 p.m. in the Sublette BOCES Boardroom at 665 N. Tyler Ave.

The second meeting will be on Wednesday, Nov 29, at 6 p.m. in Green River at Western Wyoming Community College Room #206, 1 College Way. The third is on Thursday, Nov. 30, at 6 p.m. in Jackson at the Teton County Library’s Ordway Auditorium, 125 Virginian Lane.

Written comments will be submitted to the Wyoming Game and Fish Commission at its March meeting, tentatively set for Pinedale.

To read the draft risk evaluation report, view maps and to comment, visit

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