PINEDALE, Wyo. — Thousands of mule deer, pronghorn antelope and sage grouse congregate at Wyoming's Pinedale Mesa, running around on one of the nation's biggest natural gas finds.

It is here at the mesa that wildlife shares the landscape with scattered drilling rigs, miles of new roads and hundreds of producing natural gas wells.

Geographically isolated and high above the valley floor, the 90-square-mile mesa is a unique winter range for wildlife, according to Steven Belinda, wildlife biologist for the U.S. Bureau of Land Management's Pinedale field office. The area provides winter range for roughly 4,000 to 6,000 mule deer, 2,000 to 3,000 pronghorn and 3,000 to 4,000 sage grouse.

But as natural gas assumes the position as America's fastest-growing energy source, the mesa is becoming a flash point in the debate about taking care of wildlife while meeting the nation's soaring energy demands.

Such concerns have grown this year as companies like Salt Lake-based Questar Corp. prepare to ramp up a winter drilling program. A report scheduled for release in October is certain to fuel the debate.

According to Hall Sawyer, a wildlife biologist with Wyoming-based Western EcoSystems Technology Inc. and author of the report, the mesa's wintering mule deer population has declined 46 percent over the past five years. In contrast, a separate winter range, known as the Pinedale Front winter range complex — which has no oil or natural gas production activity — showed no declines in mule deer population over the same period.

Bob Barrett, a member of the Pinedale Anticline Working Group, a committee charged with providing recommendations on mitigation measures to the BLM, said the study suggests deer and energy development are not getting along very well. Barrett places the blame squarely on the BLM.

"My contention is the deer herd is going to take a tremendous hit," Barrett said. "The deer are going off of this crucial winter range complex on habitat that will not sustain them during the worst winters."

The report comes as winter drilling on the mesa accelerates.

In the past, producers have been restricted from drilling on the mesa from mid-November through April to protect mule deer, which rely on the area's sagebrush for winter forage.

Questar was the first company to receive permission from the BLM to implement winter drilling.

Last winter, Questar was permitted to operate one pad with two drilling rigs. This winter, Questar will drill on three pads with two drilling rigs per pad. The winter drilling will continue through 2014, after which Questar has proposed a $210 million mitigation plan.