A tiny mouse vying for survival in the Rocky Mountains may have gained an upper hand over Western developers.

Scientists hired to review contradictory evidence for the U.S. Fish and Wildlife Service concluded the Preble's meadow jumping mouse is a unique subspecies, limited to parts of Colorado and Wyoming.

The study by the Portland, Ore.-based Sustainable Ecosystems Institute, obtained Sunday by The Associated Press, would help justify keeping the 3-inch mouse protected under the Endangered Species Act.

The mouse, which uses its 6-inch tail and strong hind legs to jump a foot and a half in the air, inhabits grasslands that include prime real estate along Colorado's fast-growing Front Range.

Fish and Wildlife is expected to decide by early August whether the mouse should stay on the endangered species list.

The decision affects nearly 31,000 acres designated as critical habitat to help the mouse recover. Its population has dwindled to an average of 44 mice per mile of stream because of urban sprawl.

"It's really too early to say what actions we will be taking as a result of this. Obviously, we will be according this study great weight," Fish and Wildlife spokesman Chris Tollefson said Sunday.

A fierce dispute arose earlier this year about whether the mouse is a distinct creature under the sun, with a dwindling population, or is the same as a more common species — and undeserving of protection.

It quickly became emblematic of a broader ideological clash over the Endangered Species Act itself, between property-rights advocates who want to scale back the law and wildlife advocates who want to ensure the law is science-driven.

Biologist Rob Roy Ramey, a contractor to the Interior Department, had found that the mouse was genetically identical to the more common Bear Lodge meadow jumping mouse, which isn't in danger of extinction.

His research was among the reasons cited by then-Interior Secretary Gale Norton in February 2005 when she proposed removing the mouse from the government's endangered species list. It has been considered a species "threatened" for survival since 1998.

But earlier this year, Tim King, a U.S. Geological Survey scientist, challenged Ramey's research. He said the mouse is distinct from other jumping mice.

The study by the institute, an independent organization hired by Fish and Wildlife to mediate the issue, sided with King. It found Ramey had mixed up DNA samples from Preble's and Bear Lodge mice.

Environmental advocates described it as an open-and-shut case.

"The scientists keep saying that this a unique mouse that warrants continued protection," said Erin Robertson, a staff biologist with the Denver-based Center for Native Ecosystems, an advocacy group.

"The Service should say, "OK, we've answered that question. The mouse is a good subspecies," and move on," she said of the study. "There shouldn't be any ambiguity about what the panel found."

Ramey, acting as a science adviser to Deputy Assistant Interior Secretary Julie MacDonald, also has reviewed the status of other species whose endangered status is blocking developers.

Biologists within Fish and Wildlife have criticized MacDonald for dismissing many of their concerns, particularly with regard to the greater sage grouse that roams oil and gas fields in the West.