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In recent years, fracking has surged in western North Dakota’s Bakken region—the area had just 200 active oil wells in 2005 butmore than 10,000 churn out approximately 35 million barrels of oil every month. The extraction comes with a price: The grasslands where those oil wells sit are a  and the construction isn’t boding well for the birds that live there, according to recent research conducted by U.S. Geological Survey.

“There’s a lot that’s unknown about [fracking’s effect on] the Bakken,” says Sarah Thompson, a USGS scientist. “It’s new and it’s happening really quickly.”

From 2012 through 2014 Thompson and her team surveyed 1,900 acres of land spread across seven counties in northwest North Dakota, counting and identifying any birds they observed in the transformed landscape. Fracking has turned the flat, formerly green expanses of North Dakota into a patchwork of deep red gravel well pads. Each pad is stacked with storage tanks and jacks for pumping oil, and new gravel roads support heavy truck traffic. Natural gas flares burn into the night.

“Everyone could guess that they’re not going to inhabit the gravel well pad,” Thompson says. “But the question was: How far out into the ‘undisturbed habitat’ were birds sensing there was a disturbance?”

After years of surveying the bird populations, the researchers concluded that most bird species are avoiding not only the infrastructure itself, but also the surrounding habitat—in some areas by a distance of more than two football fields. In areas within 500 feet of a multi-bore fracking site, or 875 feet from a single-bore one, bird density dropped by 33 percent. (Multi-bore sites, with bores packed together to minimize total land destruction, are a  relatively new concept—and researchers don’t yet know the specifics of why the birds appear willing to get closer to them.)

Three species, the Baird’s Sparrow, Chestnut-collared Longspur, and Grasshopper Sparrow, stayed as far as 1,800 feet from single-bore wells.

“Grassland birds do not generally respond well to the introduction of non-grassland habitat,” says Jason Hill, a Vermont Center for Ecostudies researcher who’s studied grassland birds near unconventional oil wells. “They are grassland birds for a reason.”

But cause-and-effect threats associated with the bird declines are still unclear. Drilling structures likely provide more abundant perching spots for predatory birds. Habitat destruction reduces food availability. Dust and noise from construction trucks scare wildlife away. “It might be the birds don’t enjoy taking a dust bath every five minutes,” Hill says. “It may be that it’s harder for them to find food. [That kind of research] is what’s critically needed.”

Still, Thompson’s paper does point to at least one potential improvement: The new method of consolidating multiple bores into one well pad is likely to cut down on land use, and would be an attractive financial option for oil companies that need to lease any land they use, Hill says.

Many of these species are under significant stress even without the oil fields. Half of the 10 species Thompson spotted most frequently are , according to Լ����Ƶ’s Birds and Climate Change Report. The North Dakota Game and Fish Department considers several species to be of high conservation priority, including the Sprague’s Pipit, which has been a candidate for Endangered Species Act protection since 2010. In its the U.S. Fish and Wildlife Service ruled that oil and gas infrastructure doesn’t pose a threat to the birds’ survival.

Grassland birds have already lost significant space to and . That means any help toward preserving the habitat they have left would be welcome. “It isn't really that any specific threat is particularly damaging,” Thompson says. “It is the cumulative impact of many threats.”