Wind farms pose a wider radius of risk to birds than previously thought, a new study from Purdue University and the U.S. Geological survey has found.

These findings especially matter for birds, like golden eagles, which have seen substantial population declines in some areas. Researchers looked at the carcasses and feathers from birds killed by wind turbines, discovering that they’d sometimes come from hundreds of miles away.

That means that even distant wind turbines could pose challenges in areas where the U.S. Fish and Wildlife Services have set a no-net-loss target for the golden eagle population. The study found that as many as one in four of the birds killed at Altamont Pass Wind Resource Area’s California facilities had come from another region.

The science website reports:

Worldwide, such facilities have been responsible for the deaths of 140,000 to 328,000 birds and 500,000 to 1.6 million bats, raising questions about their effects on population sustainability.

… "If you only consider local birds in an environmental assessment, you're not really evaluating the effect that facility may have on the entire population," [wildlife biologist and study co-author Todd] Katzner said.

The study’s other co-author, J. Andrew] DeWoody said that wind energy generators can receive permits that allow a certain number of unintended bird deaths. But if that number is too large, the companies could be fined. And knowing that a large percentage of the birds killed are from neighboring states could muddy the management waters.

"The golden eagle fatalities at this one site have demonstrated consequences that extend across much of the range of the species across North America," DeWoody said.

The golden eagle population is a concern for several state and federal agencies, DeWoody added. He said future research could include looking at more bird species affected by turbines.

Regardless of the environmental impact, the turbine-loving Obama administration has sought prodigal provisions for wind energy. In May, for instance, it proposed a plan that would let wind farms kill more than 4,000 bald eagles a year.

In contrast, traditional energy companies have faced hundreds of thousands of dollars in fines—as well as, in some cases, criminal charges—for killing far fewer and far less rare birds.