Early one summer morning some years ago, Eve Thomason, then a wildlife biologist for a local power utility, found a dead golden eagle near a power pole in rural Idaho. She noted that it could have been electrocuted, then moved on. Under the next pole she found a dead prairie falcon. Again, she looked up, but this time she also saw a live prairie falcon sitting on a pole that had been retrofitted to prevent electrocution. She was stumped.

Years later, she realized that the dead prairie falcon might not have been electrocuted after all. 

In a study published Aug. 1 in the journal iScience, Thomason and several other researchers revealed a grim pattern. Researchers who examined dead birds found along approximately 120 miles of power lines across four Western states discovered that the majority of them — more than 65% — were actually killed by guns, not electrocution.

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Only about 17% of the birds were electrocuted, while another 17% were killed by blunt trauma, such as collisions with cars or other birds or falling from a nest. The high percentage of shooting deaths surprised Thomason, the paper’s lead author and a research associate with the Raptor Research Center at Boise State University. Conventional wisdom has long held that power lines electrocute large birds like eagles and ravens when the animal’s talons, wings, beaks or other body parts touch exposed wires or other equipment.

“For golden eagles, shooting is one of the important components holding back growth of that population.”

But Thomason had begun to find dead birds in places where electrocution seemed unlikely — where exposed wires were insulated, for example, or spaced far apart. She and her fellow biologists — Todd Katzner and Tara Conkling with the U.S. Geological Survey, Natalie Turley with Idaho Power Company and James Belthoff of Boise State — decided to dig deeper.

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Between 2019 and 2022, Thomason and a crew of field technicians walked from one power pole to the next on public lands across the West, collecting dead birds. Some had been freshly killed, others were little more than piles of feathers. On many days, they found 15 or more carcasses under power poles and lines.

In all, they collected 410 birds in Idaho, Wyoming, Utah and Oregon, and brought the carcasses to the Idaho Department of Fish and Game’s Wildlife Health and Forensic Lab to be X-rayed, dissected and analyzed. Out of 175 birds whose cause of death they determined, they found that 42 ravens, 30 red-tailed hawks, 12 Swainson’s hawks and six golden eagles had been shot.

Thomason isn’t sure how this relates to the local bird population – whether, for example, there are more hawks than eagles in the area. Some birds, she thought, such as eagles, could have been shot, removed and sold illegally for parts. It’s also possible, she said, that hawks and ravens could simply have been targeted more frequently. Shooting is rarely studied as a possible cause of death in birds like ravens, red-tailed hawks or prairie falcons, making it difficult to determine its population-level impact, said Katzner, one of the USGS biologists who worked on the paper.

But wildlife experts do track shootings in golden eagles, and a 2021 paper listed gunshots as the top cause of all human-caused mortalities. According to the study, if an eagle died after its first year because of a human cause, it was more than likely shot. “For golden eagles, shooting is one of the important components holding back growth of that population,” Katzner said.

Thomason wondered if more birds were being shot than previously thought. So she started intercepting the dead eagles sent to Idaho’s lab repository. Many of the carcasses that were X-rayed showed evidence of gunshot wounds.  

“A lot of them had been labeled electrocution, or, based on where they were found, a couple were suspected vehicle collision,” Thomason said. Without a necropsy or X-ray, the old assumptions tend to prevail, she said.

But it’s not easy to keep people from killing raptors, said Brian Nesvik, director of the Wyoming Game and Fish Department and former chief game warden.

“It’s not an educational problem,” he said. “It’s not like you can go out and say, ‘Hey, people are screwing up, let’s educate them and they won’t do it anymore.’ These are people intentionally shooting eagles.”

And illegal shooting won’t stop unless the offenders are caught and prosecuted. That requires figuring out when and where such shooting is most likely to occur, he said.

Thomason may soon have some answers. In two follow-up papers currently under peer review, she analyzes locations and time of year, finding patterns in both that could potentially help law enforcement. She has also looked at the psychology behind illegal shootings. Some shooters see themselves as trying to protect livestock or game animals from perceived competitors, she said. But for others, the explanation is simpler.

“In cases that people have been caught shooting protected birds, we have learned that some of them do this for fun.”

For such people, she said, “it’s a hobby.”

Christine Peterson lives in Laramie, Wyoming, and has covered science, the environment and outdoor recreation in Wyoming for more than a decade. Her work has appeared in National Geographic, Outdoor Life and the Casper Star-Tribune, among others. This article is reprinted with permission from High Country News.