Skip to main content
You have permission to edit this article.
Deer numbers drop almost 40 percent as animals avoid oil and gas wells, new study shows
top story

Deer numbers drop almost 40 percent as animals avoid oil and gas wells, new study shows

  • Updated
  • 0
Mule deer

A mule deer buck walks through the Red Desert during the fall migration, heading south toward Rock Springs near the Big Sandy River. A comprehensive study was published recently showing mule deer avoid oil and gas wells, which results in smaller herds.

Mule deer don’t like oil and gas wells.

A new report — the first of its kind — analyzes 17 years’ worth of data showing that multiple generations of mule deer on the Pinedale Anticline will avoid wells on their winter range at nearly all costs.

“Mule deer and energy development—Long-term trends of habituation and abundance,” published recently in the journal Global Change Biology, outlines almost two decades of work documenting mule deer wearing tracking collars. It also provides a startling conclusion: Portions of the Sublette mule deer herd in southwest Wyoming that winter on the Pinedale Anticline are almost 40 percent smaller than they were before the oil and gas boom.

“The study shows the trade-offs of energy development in critical wildlife habitat,” said Hall Sawyer, lead author on the paper, who has worked with deer on the Anticline since the ‘90s.

The paper isn’t making a recommendation, he said. It’s simply presenting data from almost 200 mule deer on what was the largest gas field in the country.

“Twenty years ago we didn’t really have a good idea of what was going to happen, if deer would avoid these areas or it would change anything or not,” Sawyer said. “As development progressed, it became clear quickly that deer avoided well pads. It also became clear that mule deer numbers began to drop off.”

Representatives from the Petroleum Association of Wyoming had not seen the paper and declined to comment on its results.


The study started before anyone had really heard of the Pinedale Anticline or Mesa, as it was called locally. In 1997, only a few old exploratory wells dotted the landscape south of Pinedale. Rough dirt roads connected them to Highway 191.

But Ultra Petroleum was beginning to explore the area and wanted data on wildlife, everything from sage grouse to antelope, said Doug McWhirter, Jackson and Pinedale wildlife supervisor for Wyoming Game and Fish, who was the Pinedale biologist at the time.

“It’s a scenario you would always like to have, but you don’t often get that opportunity have a before, during and after look at any particular situation,” he said.

The Sublette mule deer herd was of particular interest. In the late ‘90s, it numbered in the tens of thousands and attracted trophy hunters from around the country and world.

It also migrated. The masses of big bucks, fat does and springy fawns traipsed between 18 and 80 miles from the Pinedale Anticline to four different mountain ranges following what researchers now refer to as the green wave — spring grasses offering critical nourishment.

And they wintered on the Pinedale Anticline. The roughly 100-square mile sagebrush grassland offered just enough quality food to keep most of the deer alive through the winter. They didn’t thrive there, but they eked out a living until spring.

About 5,200 mule deer wintered on the Pinedale Anticline when the study began, making it one of the biggest mule deer winter ranges in the state.

“They’re so special because of those movements. It’s what allows those deer to exist and thrive. It’s the ability to move, the ability to make use of various habitats at various times of the year and conditions,” McWhirter said. “They inhabit some of the most awesome mule deer habitat that can be found anywhere.”

Support Local Journalism

Your membership makes our reporting possible.


But those uninterrupted winters would not remain.

“In July of 2000, the BLM approved development of 700 producing well pads, 645 km of pipeline, and 444 km of access roads in the Pinedale Anticline,” according to the study.

Construction began the following near, and BLM approved another 4,400 wells in 2008.

The work was not conducted without concern for wildlife such as deer. Companies spent millions of dollars on horizontal wells, pipes to transfer liquids instead of trucking them and modified fences.

The Bureau of Land Management passed regulations saying most wells couldn’t operate during the winter in designated winter ranges.

And by 2010, most of the energy development on the Anticline was in production.

Most people, including BLM officials, believed that would be enough, Sawyer said. Once the bulk of the construction was over, deer would habituate to the well pads and return to their old habits. Sawyer’s work, which included collaboration with researchers from the University of Wyoming, BLM, Game and Fish and funding from industry, showed they would not.


Even with remediation efforts and a 45 percent decrease in hunting pressure mandated by Game and Fish, the Sublette deer herd dropped overall by 16 percent since 2001, the paper states.

The deer wintering on the Pinedale Anticline declined by about 40 percent.

“The decline is absolutely noticeable. I notice it during the hunting season and off-season,” said John Eddins, an engineer in Rock Springs who worked on highway projects for the Wyoming Department of Transportation for many years.

Eddins has hunted in the neighboring Wyoming Range herd most of his life, along with his father, grandfather and other family. While he couldn’t speak to Sawyer’s paper on energy development, he did lament the loss of prized deer his family has cherished for generations.

Why do deer avoid wells and roads?

“Because they perceive them as risky and try to keep their distance,” Sawyer said.

Unlike town deer – those that eat roses and strip young trees of bark and leaves – migratory herds haven’t grown accustomed to human influences. But the migratory herds, with tens of thousands of individuals, are also the ones supporting Wyoming’s iconic mule deer populations.

During harsh winters, deer will stray closer to wells, but at the same time they’re losing numbers because of deep snow and frigid cold. Other years, they either congregate and degrade small patches of good habitat, or live on the fringes where food is scarce.

“That’s one of the trade-offs. The study shows there’s trade-offs,” Sawyer said. “When we lose critical habitat and when we lose extra acres of habitat because of avoidance, we should expect fewer animals.”

Follow managing editor Christine Peterson on Twitter @PetersonOutside



Be the first to know

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

Related to this story

Get up-to-the-minute news sent straight to your device.


News Alerts

Breaking News