How Does Energy Development Affect Wildlife Migration Patterns?

Wyoming is home to some of the largest migrating mule deer herds in North America, and they serve as the backbone of a strong hunting tradition that supports communities and local businesses. To better understand and ultimately conserve these migrating herds, researchers are increasingly fitting wildlife with global positioning system (GPS) collars that transmit real-time data and help scientists map animal movements and provide recommendations for land and wildlife management at all levels of government. 

Hall Sawyer

Science-based management is critical in Wyoming, where mule deer populations have been in decline since the 1990s despite significant interventions to stabilize their numbers. The state has also experienced a steep increase in oil and gas development since the early 2000s, which has altered mule deer behavior and negatively affected population sizes, according to researchers.

To learn more, The Pew Charitable Trusts spoke with one of those researchers: biologist Hall Sawyer of Western EcoSystems Technology Inc. (WEST), who conducted a study, published in the July 2020 Journal of Wildlife Management, on how energy development can affect mule deer migrations. Sawyer is an adjunct faculty member in the Zoology & Physiology Department at the University of Wyoming and is a research associate with the Wyoming Migration Initiative. This interview has been edited for clarity and length.

Q:  Tell us about the mule deer herd you studied for this research.

A: Our study focused on the Sublette Mule Deer Herd—a herd that includes more than 25,000 deer that spend winters in the sagebrush flats of the Green River Basin and migrate 30 to 100 miles northwest to summer in the mountain ranges of the Greater Yellowstone Ecosystem. Much of our research is aimed at evaluating how large-scale natural gas development on the winter range affects the seasonal distribution and migration patterns of mule deer.

Q:  What are the most important findings from this project?

A: Previous research has shown that mule deer tend to speed up their migrations in areas where energy or housing development encroach on their routes, but we’ve never known just how much development these migratory routes can withstand before deer quit using them. Our study showed that migratory use by deer steeply declined when surface disturbance from energy development, such as access roads and well pads, exceeded 3% of the migration route.

Q:  How does this research relate to other studies regarding land use and mule deer populations?

A: A key component of conserving an imperiled bird like the greater sage-grouse across the West and keeping them off the Endangered Species List has been management guidelines that limit surface disturbance in core sage-grouse habitats. Our study suggests that a similar approach may be warranted for maintaining functional mule deer migration routes in regions where energy development is a prominent land use.

Benjamin Kraushaar

Q: The human population and land-use intensity in the intermountain West have been increasing in recent years, as have the challenges to managing wildlife and habitat loss.  How would you like this research to be used by federal, state, or local agencies?

A: Land managers have the difficult task of balancing competing land uses and making decisions with imperfect data. Our job is to provide managers and other stakeholders with the information they need to improve their planning and management efforts. This study can help inform decisions related to energy development and mineral leasing in areas that overlap with mule deer migration routes.

Q: Wyoming Governor Mark Gordon recently signed an executive order to identify, designate, and conserve migratory habitat for mule deer and pronghorn.  Should this research inform that policy and, if so, how? 

A: This research provides us with a better understanding of the relationship between surface disturbance and mule deer migration, which is just one of many factors to be considered by Wyoming stakeholders in the executive order policy. In years to come, we hope to identify similar disturbance thresholds for other big game species, such as pronghorn and elk, and disturbance types, including wind and solar development, that can also help inform the executive order process.