As Natural Gas Fields Grow, Pronghorn Habitat Shrinks

May 3, 2012

A five-year behavioral study shows that pronghorn in Wyoming are losing their wintering grounds to large-scale industrialization.

Intense development of the two largest natural gas fields in the continental U.S. has driven some wildlife from their traditional wintering grounds.

Over a period of five years, WCS researchers and their colleagues tracked 125 female pronghorn in Wyoming’s vast Jonah and PAPA gas fields using GPS collars. They discovered an 82 percent decline of habitat classified as “highest quality”—meaning the turf best suited for wintering animals. Widespread natural gas development in these areas, which are part of the Greater Yellowstone Ecosystem, has led to a sharp increase in well pads, roads, and other associated infrastructure. In response to these changes, pronghorn have shifted to the periphery of areas once considered crucial winter ranges.

“In our study we have detected behavioral shifts for pronghorn in response to natural gas field development and infrastructure on federal BLM [Bureau of Land Management] lands,” said lead author Jon Beckmann, of WCS’s North America Program. “By detecting behavioral changes, it is possible to identify threshold levels of gas field infrastructure development before any significant population declines. Maintaining the integrity of crucial wintering areas is particularly important in harsh winters to avoid diminishing pronghorn numbers.”

To protect pronghorn on BLM lands, WCS recommends a series of measures, beginning with the collection of baseline data on population sizes and distribution prior to any new construction. This information would help define crucial winter range and limit development in key areas. To examine the impacts of gas fields, conservationists would need to monitor habitat and population levels over time in both these developed sites as well as similar unaffected control sites. Finally, WCS recommends that gas companies employ directional drilling to reduce surface disturbance and limit habitat loss and fragmentation.

Wyoming shelters half of North America’s pronghorn, which are declining in other parts of the U.S. Herds from the western half of the state—including one from Grand Teton National Park known for making the longest overland migration in the U.S.—winter in the region that plays host to the gas fields. The mesa located above the natural gas deposits once attracted pronghorn to its windswept flat terrain, free of deep snow, but these herds are now being forced into less desirable areas.

The authors warn that pronghorn can only lose so much winter range before they will begin to decline in number. Mule deer have already declined by more than 50 percent from this region.

Joel Berger, also a WCS co-author on the study, said: “Ultimately this is a policy issue for petroleum extraction on U.S. public lands. In several cases science indicates that petroleum developments have had negative impacts on wildlife. We are hopeful that studies like these will inform future energy development on public lands in the West.”

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