An animal built to run does not need to be fast if it sees the threat early enough.
Pronghorn have enormous eyes for their body size, set wide, and they read open country for miles.
Their whole survival strategy is that nothing moves out there unless it matters.
Then a machine two hundred and sixty feet tall goes up on the ridge and turns all day, every day, forever.
It never approaches and it never leaves.
So what does an animal like that do about it?
Seeing distance is the whole resource
On sagebrush steppe there is nowhere to hide, so the herd substitutes sight lines for cover.
An object that moves constantly sits permanently inside that visual field and cannot be resolved as safe or unsafe.
The cost of avoiding it is not measured in miles walked. It is measured in food not eaten.
Winter on this range runs on one plant.
Sagebrush stands above the snow when everything else is buried, so it is the only reliable forage for months at a stretch.
Ground given up near a turbine is therefore calories given up, and a pronghorn burning body reserves in February has no way to earn them back.
That is why biologists stopped counting heads.
A herd that stays but quietly trades its best feeding ground for worse looks identical on a survey flight and is not the same herd.
The ranch, the towers and the road through it
The ground in question is the Shirley Basin, arid shrubland in Carbon County, a short drive north of Medicine Bow.
The facility sits on the Dunlap Ranch, about 24 square miles of it, and carries 74 turbines rated at 1.5 megawatts each.
With them came access roads, a substation and roughly eleven miles of transmission line.
A state highway already cut through the property before any of it went up.
The dominant cover is Wyoming big sagebrush, and the basin is crucial winter range, which is a formal designation rather than a compliment.
The herd has moved through here between winter and summer ground for as long as anyone has recorded it.
The construction did not fence them out. It put a moving object in the middle of the view.
Three separate analyses of the same collars
The first study fitted 47 adult females with satellite collars and followed them through the winters of 2010, 2011 and 2012, spanning construction.
It found no displacement at all at the scale of the whole home range. Inside those home ranges the animals avoided turbine ground after the towers went up, most strongly in the second winter, with no sign of habituation by the third.
A second analysis widened it to 166 individuals across five summers and 142 across five winters, adding data from 2018 through 2020.
Its conclusion was more cautious than the first: displacement trended upward and animals nearest the turbines did avoid them, but there was no consistent negative effect across years.
The third looked only at movement, pulling 286 migration sequences from 117 animals: 121 in spring, 123 in fall and 42 in winter.
Seven in ten of those migrations passed within 0.6 miles of a turbine.
But stopover choice moved. Pushing that distance from zero to 0.6 miles raised the relative probability of a site being chosen by 33 percent in spring and by 300 percent in winter.
What 300 percent does not mean
Relative probability of selection is not a head count and not a calorie.
It says which pixel an animal preferred, not how much it lost by preferring it, and nobody has weighed a doe or counted a fawn against that number.
Route fidelity fell near turbines under construction, but the routes themselves still went through.
Every collar in all three studies sat on an adult female, so there is nothing here about bucks, nothing about fawns and nothing about survival.
There is also a six year hole in the middle where no animal was tracked at all.
The signal that emerges is real but modest, closer to the small shifts seen when flying species reroute around turbine arrays than to abandonment, and the same pattern shows up across working prairie elsewhere in the state.
Why the modest answer is the useful one
A herd that leaves is a headline and a policy problem.
A herd that stays and shaves a little off its winter budget every year is neither, and it is far harder to argue about.
The practical value of more than a decade of collars is that it points at siting rather than at wind power itself, because the effects scale with how close a turbine sits to the ground animals were already using, as the federal survey summary puts it.
Move the row, keep the stopover.
The researchers themselves frame the result as incremental change rather than collapse, and their own warning is about accumulation over a lifetime, as the university project page makes clear.
The collared pronghorn are still crossing the basin.
What nobody can price yet is what the detour costs them.
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