(AP) The federal government needs to impose new restrictions on oil and gas development in the West because current policies are failing to protect sage grouse, according to conservationists citing a new study of the birds in western Wyoming.

With all the oil and gas development going on now and planned in the future, "care really must be taken if we're going to have these wide open ecosystems in the future," Erik Molvar, a wildlife biologist with the Biodiversity Conservation Alliance in Laramie, said Thursday.

Sage grouse inhabit large areas of the western United States, including Wyoming, Colorado, Utah and Montana, where energy development is booming.

The health of sage grouse has been a concern of conservationists and wildlife managers because of the loss of habitat to agriculture, energy and other human development. Their numbers have dropped from historical levels of about 16 million in the United States and Canada to fewer than 150,000 by some estimates.

But the federal government has rejected listing the ground-dwelling bird under the Endangered Species Act, saying conservation efforts among local, state, federal and private entities were adequate.

The study cited Thursday was conducted by University of Wyoming doctoral student Matthew Holloran for his dissertation. It was paid for by the Bureau of Land Management, the state Game and Fish Department and oil and gas companies.

Holloran wrote that he found that sage grouse appear to avoid leks _ traditional courting grounds where males compete for females _ the closer they are to oil and gas activity. He found declines in breeding males in leks within 3.1 miles of drilling rigs.

In addition, he said the affects on grouse behavior and populations continued even after oil and gas activity ended.

Holloran, who has since graduated and could not be reached for comment Thursday, studied a roughly 420-square-mile area in the upper Green River Basin near Pinedale in western Wyoming.

The BLM has acknowledged that sage grouse can be affected by oil and gas development. Since 2000, the agency has imposed various operating restrictions on drilling activity in the vicinity of sage grouse leks and has required companies to closely monitor any impacts on wildlife.

However, Holloran concluded that the BLM's current policies aren't enough.

"I suggest that current imposed development stipulations are inadequate to protect greater sage grouse, and that stipulations need to be modified to maintain populations within natural gas fields," Holloran wrote.

Conservationists who participated in a conference call with media on Thursday stressed they were not seeking to stop oil and gas development in the West.

Linda Baker, community organizer with the Upper Green River Valley Coalition, said sage grouse and other wildlife need refuge from development, noting that 7,000 to 10,000 more wells may be drilled in western Wyoming.

"We can have both energy development here, and we can have healthy populations of wildlife," Baker said.

Molvar and others advocated that the BLM require companies use directional drilling, where one well can do the work of multiple conventional wells by drilling at an angle. However, directional drilling is more expensive.

Molvar argued that any additional cost is minuscule given the value of the natural gas that can be produced.

Tom Christiansen, sage grouse program coordinator for the Wyoming Game and Fish Department, was out of the office until Monday and unavailable comment.