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Jerret Raffety, AP
This May 9, 2008 file photo, shows a male sage grouse fighting for the attention of female sage grouse southwest of Rawlins, Wyo. A new report commissioned by the Pew Charitable Trust shows that greater sage grouse populations in 11 Western states have declined more than 50 percent over the last six years, indicating the imperiled bird is worse off than previously thought.

SALT LAKE CITY — A new study of the greater sage-grouse’s population finds that the bird’s numbers decreased 56 percent between 2007 and 2013, leading to the conclusion that the sage-grouse is at even greater risk than biologists thought and suggesting that conservation efforts are largely failing.

The research, commissioned by the Pew Charitable Trusts and conducted by Edward (Oz) Garton, professor emeritus in wildlife ecology and statistics at the University of Idaho, represents the most comprehensive population update since 2011.

"This report provides definitive evidence about the fragile state of the greater sage-grouse, an indicator species for the health of the interior West’s sagebrush region — where hundreds of other wildlife and plant species also live,” said Ken Rait, director of Pew’s U.S. public lands project. “We hope that this latest data will be used by the BLM and Western states to develop strong science-based land management plans that responsibly balance adequate protection of the sage-grouse and this important habitat with energy development and other land uses across the interior West.”

The grim news comes as 11 Western states that include Utah gird for a possible listing of the bird this fall, with the U.S. Fish and Wildlife Service scheduled to make a decision in September.

Adding the imperiled bird to the protections under the Endangered Species Act would have far-reaching impacts on energy development, grazing and other types of activities on public land, including where and how renewable energy projects are carried out and the installation of transmission lines and other infrastructure.

In Utah, officials estimate a listing would have a $41 billion impact on oil and gas development alone.

Last week, Rep. Chris Stewart, R-Utah, joined other members of Congress who have introduced legislation seeking to block a listing of the bird.

Stewart's bill, the Sage Grouse Protection and Conservation Act, calls for states to implement their own strategies in lieu of the federal action and requires the U.S. Department of Interior to implement a strategy on rangeland wildfires, one of the top threats to the species.

The greater sage-grouse is a football-size bird that has seen more than 40 percent of its historical range eliminated, and its populations challenged by habitat fragmentation, wildfires, invasive species and urban encroachment.

More than half the bird's remaining habitat occurs on land managed by the Bureau of Land Management, which is releasing plans for 50 million acres of sage grouse habitat later this spring.

Those plans are in tandem with state management plans that have been adopted throughout the West and a handful of executive orders issued by Utah, Montana and other states that bolster protections contained in the state approaches.

In the Pew report, called "Greater Sage-Grouse Population Dynamics and Probability of Persistence," evidence pointed to a sharp decline in the number of breeding males — from 109,990 in 2007 to 48,641 in 2013 — and noted that populations across the bird's range are declining far beyond what even the best models forecasted.

“Our research should and must ring alarm bells,” Garton said. “These numbers indicate to us that if significant protections aren’t established, this important bird and the entire sagebrush steppe region face irreparable harm.”

The report used male population data provided by 10 of the 11 states where sage grouse are found (Colorado being the exception) to provide an analysis of how populations are doing. In Utah, the report looked at distinct populations found in the northeast portion of the state, in Sanpete and Emery counties, Morgan and Summit counties, and Tooele and Juab counties.

While the breeding population decreased in south central Utah by 18 percent, the male sage-grouse population actually increased over the six-year period in Tooele and Juab counties by 29 percent.

Utah wildlife officials say the fragile species routinely experiences some volatility in numbers, but the last three years has shown the population actually "cycling" up and increasing. They point to numbers which show overall, sage-grouse populations jumped 40 percent from from 2014 over 2013.

Since 2006, more than a half million acres of sage grouse habitat in Utah have been restored or improved, and Utah's plan targets more than 90 percent of the bird's range within the state, or 7.5 million acres.

Allison Jones, executive director of the Wild Utah Project, said Utah's sage-grouse numbers may be on the uptick, which is good, but the question remains whether they can be sustained long term.

"The Garton sage grouse scientist team's range-wide analysis for all the population data for the seven-year span is sobering to see," she said. "What really matters is that Utah's and the other states' populations reach a 'high' mark in the next few years that is higher than the last high, and that the next low in about 10 years is higher than this last, unprecedented low. This is how we point to a turnaround in the last 20-, 40- or 60-year long-term population trends."

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