Brewer's Sparrow nestlings are more vulnerable to predators in areas disturbed by energy development in Wyoming's sagebrush. Photo: Lindsey Sanders

Conservation

In Sagebrush Country, Drilling Brings Nest-Raiding Rodents

Scientists and federal experts are finding that habitat restoration in oil and gas fields can have unexpected consequences for Wyoming's songbirds.

Greater Sage-Grouse are media darlings. Just as the male’s haughty, heaving springtime dance woos mates from miles around, the species has attracted headlines and become a mascot of sorts for efforts to protect the West’s sagebrush steppe from energy development and other threats. The sage-grouse deserves the spotlight, too: Its numbers plunged by more than 50 percent between 2007 and 2013, and habitat lost to sprawling oil and gas infrastructure is a key factor. And with Interior Secretary Ryan Zinke intent on scrapping a carefully crafted conservation plan to preserve its ecosystem across 11 states, the species faces a forbidding future. But it’s just one of nearly 300 bird species in the sagebrush, and is not the only one losing ground.

Like the Greater Sage-Grouse, Brewer’s Sparrow, Sagebrush Sparrow, and Sage Thrasher nest only in the sagebrush, and all three are declining. Pipelines, well pads, and access roads built by oil and gas companies have sliced and flayed their habitat, leading the Wyoming Game and Fish Department to label all three songbirds as “species of greatest conservation need.” Teasing apart how those birds respond to energy development has been a nearly decade-long project for Anna Chalfoun, an ecologist with the University of Wyoming and U.S. Geological Survey. The more Chalfoun and her colleagues learn about the industry's impacts, the clearer it becomes that it’s not only the act of drilling that affects these sensitive songbirds—it also matters what happens to the land after the work is done.

Wyoming has more sagebrush than any other state, and about two-thirds of it sits atop oil and gas reserves. It was that overlap of sensitive habitat, declining songbirds, and intensifying energy development that led Chalfoun to take up this line of research in 2008. “We have some of the last contiguous chunks of sagebrush in the West,” she says. “So I feel there’s a strong impetus for us to understand what it means to fragment that habitat further.”

A growing focus of her work has been the results of restoration. When their work is finished, energy companies have to replant vegetation to “reclaim” any areas cleared or otherwise disturbed by drilling infrastructure. In return for cleaning up their mess, they get a refund on bonds they post before breaking ground. But that’s easier said than done. Plant communities in dry environments tend to recover slowly from disturbance, and that’s especially true of Wyoming sagebrush.

In western Wyoming's Jonah Field, natural gas and sensitive sagebrush overlap. Photo: Lindsey Sanders

That long rebound period raises the stakes of energy development for sagebrush songbirds. One measure Chalfoun and collaborators use to gauge the industry’s impact on birds is nesting success: the percentage of nests where at least one chick lives long enough to fledge. Their research shows that overall habitat disturbance, including reclaimed parcels, pipelines, and roads, is a more important factor in nest-success rates than the number of wells in the area. For instance, only 32 percent of Sage Thrasher nests were successful in heavily disturbed areas, Chalfoun found, compared to a 65 percent in undisturbed sagebrush. Nest success in heavily disturbed areas also plunged by nearly half for Sagebrush Sparrows and by about one-third for Brewer’s Sparrows.

Chalfoun knew from previous studies that predation was the main reason nests fail, so she set up camouflaged video cameras in the sagebrush to identify predators. The footage revealed nest raids by nine species such as raptors and raccoons, but the biggest killers by far were rodents like deer mice and ground squirrels. “That the mice are such a significant nest predator has been super surprising,” Chalfoun says. “It’s gory sometimes. They aren’t just stealing eggs.” Indeed, the videos showed deer mice maiming and dragging away thrasher nestlings roughly double their size.

Fluorescent powder helps researchers track nest-raiding deer mice. Photo: Kristina Harkins

Chalfoun also counted more than twice as many deer mice in disturbed areas, including reclaimed land, than in intact sagebrush. Something about the disturbances attracted rodents, it seemed. To investigate further, Chalfoun’s graduate student Lindsey Sanders took the project in a psychedelic direction: She captured deer mice along the edge of reclaimed parcels and brushed their fur with fluorescent powder, which glows under ultraviolet light. Sanders returned at night to discover glowing trails through the reclaimed areas, exposing them as popular mouse haunts.  

But every good hangout spot needs food. By analyzing DNA in fecal samples, a lab confirmed that the mice Sanders captured had noshed on common timothy, basin ryegrass, and Russian thistle—plants that were sown on reclaimed sites. The vegetarian buffet that follows reclamation, it appears, is attracting rodents, which supplement their diets by raiding the nests of imperiled songbirds. “Now we know a little more about why energy development is drawing in these nest predators that are leading to lower nest survival,” Sanders says.

The findings from Chalfoun’s lab demonstrate that sagebrush ecosystems are complex, and truly reclaiming them isn’t as simple as planting some seeds. “When I got started in the field of land reclamation, it was called re-vegetation,” says Peter Stahl, director of the Wyoming Reclamation and Restoration Center, who works with energy companies to improve their reclamation. “Now we’re all about wildlife habitat restoration here in Wyoming. We’re trying to get native-plant communities restored and get habitat restored.”

Wyoming considers Sage Thrashers a species of greatest conservation need, due to habitat degradation from energy development. Photo: Tayler Scherr

Sagebrush is included in the seed mixes for reclamation, but it takes an eternity to grow compared to mouse-friendly grasses and forbs; big sagebrush, a dominant species in much of the West, needs nearly a century to recover on its own in Wyoming, one recent study found. Reclamation may accelerate that process, “but even then, success in establishing big sagebrush on oil and gas wells with current re-vegetation methods has still been very low and very slow,” says William Lauenroth, a Yale University plant ecologist who co-authored that paper. His work has shown that reclamation in Wyoming oil and gas fields accelerated grass recovery, but did not bring back sagebrush or perennial forbs any faster than on sites that were simply abandoned.

One challenge to better reclamation, Lauenroth and Stahl say, is the contrasting set of standards energy companies are held to on lands they lease across the West. Reclamation requirements are up to private landowners on private lands, state agencies on state lands, and the Bureau of Land Management (BLM) on federal lands. “It’s definitely a patchwork,” Stahl says. “Within BLM, just about each district office has its own set of standards that companies have to meet. They need to make their regulations a little bit more uniform.”

Hungry deer mice sometimes kill Sage Thrasher nestlings twice their size. Photo: Lindsey Sanders

Another problem is that drillers need a tastier carrot to make reclamation worthwhile. “The companies are putting up a bond that is absolutely ludicrous, it’s so small,” Lauenroth says. “They don’t have much incentive to invest in making sure these sites recover.” The nonpartisan U.S. Government Accountability Office agreed in a 2011 report, noting that BLM’s minimum bonding amounts hadn’t been updated in 50 years and were likely too low to compel drillers to complete reclamation projects.

Ashlie Fahrer, a public affairs specialist for BLM, wrote in an email to Audubon that the agency is working to make its reclamation standards more uniform and measurable, and has issued a policy to periodically review bonding requirements. BLM is also designing a project to increase the quality and quantity of seed available for reclamation projects, she noted.  

There are other ways to speed up sagebrush habitat recovery, though. Planting nursery-grown seedlings instead of just spreading seed would help, Lauenroth says, and so would a greater focus on preparing soils before planting. Reclamation is already expensive, and doing it better will only increase the price tag. But if we’re asking the sagebrush steppe to support both continued energy development and healthy songbird populations, it may just be the cost of doing business.

Correction: An earlier version of this story incorrectly identified ravens among the species caught on tape raiding songbird nests. 

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