LARAMIE – A sage grouse study just completed in the Powder River Basin, a PhD dissertation by Brett Walker of the University of Montana, highlights the vulnerability of sage grouse to West Nile virus and coalbed methane development. The study has important implications for the bird’s prospects for survival in the Powder River Basin and other fragmented habitats in lower-elevation portions of its range.

Portions of the study focusing on the impacts of CBM drilling and production on sage grouse declines have already been published in the Journal of Wildlife Management and Avian Diseases, but two newly-released chapters focus on the danger that West Nile virus poses to fragmented populations of sage grouse already suffering from industrial development and associated habitat loss.

According to the study, “West Nile virus was a persistent new source of mortality in greater sage-grouse in the Powder River Basin that has the potential to reduce annual population growth and cause severe local population declines during outbreaks.” (p. 181).

The study found that the population impacts of the most severe local outbreaks of West Nile virus on the sage grouse population in the Powder River Basin could be as great in magnitude as the impacts from intensive energy development, and an order of magnitude greater than the impacts of vehicle collisions, powerline collisions, or hunting.

Population declines of sage grouse in Montana and North Dakota have resulted in the reduction or elimination of sage grouse hunting seasons being considered there, and officials in these states have raised the possibility of new outbreaks of West Nile virus, which is carried by mosquitoes, in these areas. Earlier research has linked mosquito production with the multitude of reservoirs built to hold coalbed methane wastewater in the Powder River Basin.

“West Nile could wind up being the straw that breaks the camel’s back as far as sage grouse survival goes in the Powder River Basin,” remarked Erik Molvar, Wildlife Biologist with Biodiversity Conservation Alliance. “This study has important implications for Endangered Species listing for the grouse, because sage grouse populations in the Powder River Basin and in the Dakotas and Montana are threatened with disappearance across a significant portion of their nationwide range as a result of the combined effects of West Nile virus and oil and gas development.”

The study noted that West Nile outbreaks could lead to major reductions in local populations, and that it is unclear how long population recovery would take or even if it could happen at all.

“The low-elevation populations of sage grouse in the eastern part of their range appear to be most vulnerable to West Nile virus based on the results of this study, and conversely, higher-elevation populations in southwest Wyoming and northwest Colorado should be a prioritized for conservation due to a lower apparent likelihood of West Nile outbreaks there,” said Molvar. “When populations become isolated by the types of habitat fragmentation that we’re seeing as a result of coalbed methane drilling in the Powder River Basin, the isolated populations that remain are especially vulnerable to being wiped out by random events such as West Nile outbreaks.”

At the same time, infection rates in undeveloped habitats and mortality during outbreaks are such that immunity to West Nile is likely to spread only slowly, the study concludes.

The study is available online at http://www.forestry.umt.edu/personnel/faculty/dnaugle/pdfs/Walker2008Dissertation.pdf.

Contact information:

Erik Molvar, Wildlife Biologist, Biodiversity Conservation Alliance, (307) 742-7978
Dr. Dave Naugle, Professor of Wildlife Biology, University of Montana, (406) 243-5364