BILLINGS, Mont. -- Federal wildlife officials say a recommendation on whether sage grouse belong on the endangered species list could be delayed until next summer.

Sage grouse have taken a heavy toll in recent decades from grazing, oil and gas drilling, wildfires and residential development. But with estimates of anywhere from 100,000 to 500,000 of the birds scattered across 11 states, there's been sharp disagreement over whether they are in imminent danger.

A decision on the chicken-sized ground bird had been expected by the end of this year. But U.S. Fish and Wildlife Service officials said Friday they will put off their recommendation following a delay in publication of the latest scientific research into the species.

Fish and Wildlife Service biologist Pat Deibert said the journal Studies in Avian Biology expects to publish the new research in the summer of 2009. More than two dozen scientists are contributing their work on sage grouse populations, including threats to the bird's habitat.

"It has a lot of good, up-to-date science we'd like to see before we make a decision," Deibert said.

Deibert added that it was uncertain whether a recommendation would be ready in time for a May 2009 deadline imposed by a federal judge. That date was set after the Western Watersheds Project successfully sued over the Fish and Wildlife Service's 2005 decision not to list sage grouse as endangered.

A study released in October by an environmental group that advocates federal protection for the bird concluded fourth-fifths of sage grouse habitat is adversely affected by either livestock grazing, natural gas and oil development or invasive weeds.

Nevertheless, Deibert said a delay in any new protections for sage grouse was not likely to have a major impact on long-term survival.

"We don't have any evidence the bird will be gone tomorrow if we don't take action in the next few months," she said.

Erik Molvar with the Biodiversity Conservation Alliance, a group that has pushed for more protections for sage grouse, said waiting for the new research is the right thing to do.

Molvar and other environmentalists had been concerned the Bush administration would try to push, in the administration's last days, a decision against listing.

"It's heartening they're going to be waiting for the science to come in, instead of rushing forward with a decision," Molvar said.

Meanwhile, states including Wyoming have been crafting sage grouse conservation plans that include putting some lands off limits to energy or agricultural development. State officials have said they hope their efforts will demonstrate adequate protections for the bird already are in place.

The Bureau of Land Management, which oversees energy and agriculture activities on much of the West's public lands, has pursued a similar approach in Wyoming's Powder River Basin. The bureau has advocated limits on energy development in some locations considered crucial to sage grouse survival, such as breeding areas.

If the Fish and Wildlife Service ultimately recommends a threatened or endangered listing, Deibert said it could take an additional year to make the listing final. In that time, she said, her agency would weigh whether the steps taken by Wyoming and the BLM were enough to keep the population viable.