Primary Investigator: Hall Sawyer, Western Ecosystems Technology Inc.
Funding: Questar, Ultra Petroleum, Bureau of Land Management (BLM), WY Game and Fish Department (WGFD)
Period of Study: 2000-2007

Area Description: The study area was located in the northern portion of the Pinedale Anticline natural gas field, situated in southwestern Wyoming. The Pinedale Anticline Project Area (PAPA) contains one of the largest and highest densities (19-30 deer/km2) of mule deer winter ranges in Wyoming, providing crucial winter range for 4,000-5,000 mule deer. Large portions of these mule deer seasonally migrate 80-200 km from their winter ranges to summer in four different mountain ranges. Natural gas reserves lie directly beneath crucial winter range for the majority of the region's pronghorn and mule deer.

Development: Beginning in 2000, the BLM approved the construction of 700 producing wells, 645 km of pipeline and 444 km of roads. More than 1,300 acres of direct habitat loss (mule deer winter range) has occurred thus far on the Mesa from the construction of well pads and access roads. The BLM is currently proposing to include an additional 4,399 wells (a 7-fold increase), causing up to 12,278 acres of additional disturbace.

Pinedale Anticline Natural Gas Field, 1986 / Skytruth	Pinedale Anticline Natural Gas Field, 2005 / Skytruth

Study Results: Researchers used global positioning system (GPS) locations to examine movement patterns of adult mule deer. Results indicate winter habitat selection and distribution patterns of mule deer were afected by well pad development and to a lesser degree, access roads.

• Changes in habitat selection appeared to be immediate (i.e. in the first year of development) with no evidence of well-pad acclimation or habituation.
• Mule deer selected areas farther away from well pads as development progressed, suggesting avoideance. Thus, indirect habitat loss may be substantially larger than direct habitat losses.
• Natural gas development displaced mule deer to less-suitable habitats. By year three of development, 41% of areas orignially identified as "high use" before development changed to "medium-high" or "low use" areas and 40% of "low use" areas had changed to "medium-high" of "high use" areas. This change suggests a greater use of less-preferred and presumable less-suitable habitat, potentially influencing survivial and reproduction.
• Mule deer abundance steadily declined by 46% in the first four years of development (2000-2004) and then appeared to stabilize in the 5th year (2005). The WGFD reported a 19% decline in deer numbers for the entire herd following the severe 2003-2004 winter, leading to the conclusion that the additional 27% reduction in the study area is likely the result of a combination of emigration and reduced survival rates.

Management Implications:

• Mitigation measures should consider all human activity across the entire project area (not just crucial winter range) and not be restricted to the development phase.
• Disturbance can be reduced thru directional drilling, limited public access, and developing road management strategies.
• Direct and indirect habitat losses have reduced the carrying capacity of this important winter range. Because deer migrate to four different mountain ranges, the effects of gas development are not limited to the winter range, rather they are seen across a much larger area of western Wyoming.