CHEYENNE (AP) - Several recent studies have concluded that energy development practices in Wyoming are hurting the state's sage grouse populations. Now, some environmentalists say the studies could provide ammunition for a renewed effort to place the birds on the federal endangered species list unless the federal government steps up its protection efforts.

Recent petitions to list the sage grouse as endangered have been rejected by the U.S. Fish and Wildlife Service. If the bird were listed, it could subject energy companies as well as ranchers to more stringent regulations.

David Naugle, professor of wildlife biology at the University of Montana, said the sage grouse used to range over much of the West. But he says the birds have now lost about half of their former range, while remaining populations have declined from 15 to 90 percent.

Several studies released in the last year have found that sage grouse populations have decreased in Wyoming's Powder River Basin and in the large gas fields in the western part of the state. Meanwhile, plans call for similar energy development in the state's Red Desert, one of the bird's remaining strongholds in the state.

In addition to energy development, scientists point at some grazing practices as well as West Nile virus as factors in the bird's decline.

Because the U.S. Bureau of Land Management has already leased much of the undeveloped federal lands in the grouse's remaining range, some environmentalists say only a change in the way the BLM allows energy companies to develop the land could protect the birds and prevent putting them on the federal endangered species list.

"We've provided the science to those decision makers, and it will be in their hands to make up their mind on what direction we're to go," Naugle said. "But the one thing I have to remind folks is the longer we wait, the few options will be available, because development is occurring very quickly."

Naugle said he has provided the BLM with detailed maps of the Powder River Basin that show remaining good winter range for the grouse outside developed areas.

He said that if the BLM would increase protection for grouse habitat, "I think we would at least have a fighting chance at a strategy that could keep birds in the Powder River Basin."

Given that the Powder River Basin is the largest natural gas field in the West, Naugle said that what happens there is likely to set national policy for all other areas where federal leases have been sold.

Cindy Wertz, spokeswoman for the BLM, said her agency is concerned about the condition of the sage grouse in the Powder River Basin and said keeping it healthy is one of the agency's goals.

"We do have current steps for oil and gas development," Wertz said. "That's what we're going with because we just don't have enough data or information, nor do we know enough to change practices."

Wertz said her agency is working with Naugle and has received preliminary data from him. But she said this is the first year of a three-year study and said a final report on the first phase isn't due out until January.

Some say that this year's new studies on the condition of the birds could lead to environmentalists filing another petition unless there's a change in federal policy.

"When (former Interior Secretary Gale) Norton denied listing, she said we can do it better without listing," Mark Salvo, director of the Sagebrush Sea campaign, said this summer. "I think what we've noticed here in the past 16 to 18 months is that it's not doing what's necessary to save the grouse."