Investigators: Joel and Kim Berger, Jon Beckman, Wildlife Conservation Society
Funding: Shell, Ultra Petroleum, Anshutz Exploration, WY Game and Fish Department (WGFD)
Period of Study: 2005-2010
** This report summarizes the first year of a 5-year study, therefore analyses are preliminary and subject to change and interpretation**

Area Description: The study took place in the Upper Green River Basin (UGRB) in southwestern Wyoming. The UGRB includes a portion of the Greater Yellowstone region and provides winter habitat for 100,000 elk, pronghorn, mule deer, moose, and bighorn sheep. This area also includes two major natural gas fields - the Jonah Field and the Pinedale Anticline Project Area, including the Mesa. The region in and around the southern portion of the Mesa has been designated by the WGFD as crucial winter range for pronghorn antelope.

Development: With the signing of the Record of Decision (ROD) in 2000, the Bureau of Land Management (BLM) approved the construction of 700 producing wells, 645 km of pipeline and 444 km of roads for the Pinedale Anticline Project Area. Additional wells (3,399) are currently being proposed. The ROD for the Jonah Infill Drilling Project was signed in March 2006, permitting year-round drilling of approximately 3,100 additional oil and gas wells to an existing 500. Maximum permitted total surface disturbance on the Jonah field is 14,030 acres.

Study Results: During the first year of the study, 48 adult female pronghorn were fitted with Global Positioning System (GPS) radio-collars, yielding 56,992 locations. Natural gas development (gas fields, roads and associated human infrastructure) was found to alter the suitability of habitat for wildlife. The continual fragmentation of this previously undisturbed open landscape has resulted in avoidance of heavily developed areas by pronghorn.

• No collared pronghorn used areas within the Jonah Field, which had previously been important winter transition range.
• Researchers documented reduced use and abandonment of habitat parcels that were less than approximately 600 acres in size.
• Pronghorn did not change their 24-hour activity pattern to forage in the habitat near well pads, even at night when human disturbance was reduced.
• Areas within 100m of gas wells were also consistently avoided.