So in 2006, BP hired Joseph Kiesecker, a lead scientist with The Nature Conservancy, to devise a method to guide Jonah-funded projects and measure outcomes. The Conservancy had been compiling data on biodiversity in Wyoming for more than a decade to determine conservation priorities. Working with the Jonah Interagency Office, Kiesecker used that data in a computer model  to identify key species displaced by development, and to suggest mitigation elsewhere to compensate for those losses. The offset program assumes Jonah will be a total loss for burrowing owl habitat, for example, so it sets a goal of preserving and restoring 33,828 acres for owls off-site. Kiesecker's team and the Jonah office selected nine biological targets, which include preserving or restoring six sage grouse leks, or breeding areas, 8,483 acres for the rare Cedar Rim thistle, and 19,121 acres of pronghorn migration routes. Kiesecker says preliminary results indicate the Jonah mitigation fund is successfully preserving places with those values.

The fund has helped purchase 13 conservation easements in just three years on an area larger than the Jonah infill -- doubling the acreage previously under easement in the Green River Valley. Many protect important linkages between high-elevation summer range on national forest and lower-elevation wintering grounds on BLM lands. And all but one include conservation-oriented grazing plans, covering both private land and tens of thousands of acres of adjacent grazing allotments on public lands.

The plans call for running livestock only at certain times or fencing certain areas to improve sage grouse range. If grazing is delayed, spring wildflowers can flourish, increasing the abundance of insects, critical food for sage grouse chicks. The Carney family's more than 8,000-acre grazing allotment on nearby national forest, for example, has been designated as a temporary grazing reserve for cattle from other allotments in need of restoration.

The Conservation Fund, a nonprofit that helps local governments and conservation groups preserve land, has done the bulk of the deals -- six easements, covering just under 10,000 acres -- with about $4.5 million from Jonah and another $5.7 million from other partners. In June, the Jonah Fund contributed $5 million (with another $6 million from the Pinedale Anticline fund) to the landmark $19.7 million purchase of development rights on about 19,000 acres of the Sommers-Grindstone ranches in Sublette County, where the Jonah Field is located. In addition to protecting wildlife habitat, the arrangement guarantees public fishing access along nearly five miles of the Green River.

Such deals head off another major threat to the remaining sagebrush habitat in this corner of Wyoming: housing sprawl, with its associated fencing, traffic and pets. Sublette County's population grew by nearly 50 percent over the last decade while the rest of the state grew by 10, according to the U.S. Census Bureau. The Carneys had their ranch under contract to sell before they decided to go with the easement and prevent future development on 2,400 acres. The family previously donated an easement on another 1,400 acres and is working to place the ranch's remaining unprotected areas under easement as well.

But conservation easements don't necessarily prevent future oil and gas drilling, especially if the landowners don't hold rights to the underground minerals. The Carney family owns the ranch's mineral rights and agreed to prohibit energy development within the easement. For easements where families don't own the minerals, Kiesecker's model estimates the risk of future drilling so managers can take it into consideration before deciding to buy an easement.

Kiesecker and others stress that, in general, the Conservancy model is best applied prior to drilling in order to identify trade-offs before decisions are made. Some areas are irreplaceable and should be put off-limits altogether, he adds.

The amount in the fund is also an issue. No efforts were made to calculate what it would actually cost to replace what is being lost from the Jonah Field, says Rollin Sparrowe, a retired federal wildlife biologist and a member of the Theodore Roosevelt Conservation Partnership, which is suing the BLM over drilling's impacts on wildlife in the nearby Anticline. "Not only is the $24 million picked out of the air, how can anybody conceive of that even being adequate?"

Linda Baker of the Upper Green River Valley Coalition, an environmental watchdog group, also worries that there has been no clear protocol for selecting projects and monitoring outcomes on the ground. She has asked the interagency office to verify how each project is replacing lost habitat and to report those results to the public. She and other critics say not enough is being done to measure which drilling activities are having the greatest impact on wildlife.

Wyoming Game and Fish habitat biologist Dan Stroud, who works in the Jonah office, acknowledges that one study meant to measure the current quality of wildlife habitat within the Jonah Field is three years overdue. Baseline data has been collected, he says, but state and federal agencies are still trying to figure out the best way to analyze it. The Jonah Interagency Office also says it will monitor all fund-related wildlife projects. Game and Fish already routinely monitors wildlife population trends, and the fund has paid for baseline plant surveys that will be used to track range improvements from the planned seasonal grazing rotations.

Stroud believes the fund has clearly helped wildlife. On a summer morning before sunrise, state biologists gather on the Cottonwood Ranches, where drilling money has helped pay for conservation easements on almost 4,670 acres, including 12 miles of riparian habitat, and a grazing plan for 36,000 acres of adjacent BLM land. In routine surveys over the past three years, the biologists have counted from 84 to 265 birds along four miles of stream here. Though extremely variable, the numbers are consistently high, indicating that this is some of the Upper Green River Valley's prime grouse habitat.

Without the fund, Stroud says, this willow-lined creek through sagebrush uplands, which offers ideal access to water and shrubs for grouse to raise chicks, might have been covered with houses.  Now, it's protected for wildlife, he says. "The Carney, Cottonwood and Sommers-Grindstone are probably some of the highest-value easements that we've got."