BOISE, Idaho — In Idaho and the Mountain West, utility poles and power lines are often the tallest feature across the landscape, providing birds with a vantage point and the perfect place to perch, hunt or nest.
The common assumption has been that electrocution therefore is the greatest threat to birds along these lines. Eve Thomason, lead author and research associate in the Raptor Research Center at Boise State University, and her colleagues set out to test that premise.
The results of their new study, published this month in the journal iScience, were surprising.
The researchers determined the cause of death for 175 birds — and found that 66% of them died from gunshots. By comparison, deaths by electrocution or by collision were split almost evenly, at around 17% each.
“This is more prevalent than we previously realized,” said Todd Katzner, senior author on the study and a wildlife biologist at the U.S. Geological Survey.
These bird shootings were illegal
The birds were species protected by state and federal laws — bald eagles, golden eagles and several kinds of hawks among them.
Thomason and Katzner laid out the legal layers of protection on these animals in a video interview with The Idaho Statesman.
“Raptors and corvids are protected under the Migratory Bird Treaty Act, and eagles are protected under the Bald and Golden Eagle Protection Act,” Thomason said.
On top of that, “anything that’s a native species is protected,” said Katzner. “Many of these birds, most if not all of them, are also protected by state law.”
They said that every bird found shot to death during the research was a protected species, other than a single pigeon.
That left an overriding question as a result of their study: Why are so many protected birds being shot? The answer, Thomason said, was “probably really complicated.”
CSI, but for birds
For the study, trained observers repeatedly walked or drove along 122 miles of power lines in Idaho, Wyoming, Utah and Oregon, and collected a total of 410 dead birds.
“Typically, we would work in teams of two, and so we would kind of leapfrog each other,” Thomason explained.
The observers would walk along the power lines and scan about 10 meters on each side, collecting dead birds in coolers along the way.
“We could go weeks without finding a single bird,” Thomason recalled, “but then we could come into 5, 10, 15 in a single day.”
To understand cause of death, each carcass was delivered to the Idaho Department of Fish and Game Wildlife Health and Forensic Lab for a full examination, including inspection for visible injuries, photographs and X-rays.
Past research, in part conducted just south of Boise, “really focused on electrocution as the primary cause of death of these birds,” Katzner said. But those surveys carried out only “a small number of necropsies on birds in very good condition.”
The novelty of the new study is that it looked more comprehensively at affected populations.
“Eve X-rayed every single bird that she found, whether it was just a pile of feathers or bones, or it had died 10 minutes before (she) got there,” Katzner told the Statesman, emphasizing the magnitude of work that went into the research. “And because of that, she found stuff that was unexpected and surprising.”
Among the list of carcasses found, some were impossible to categorize down to species level. Still, the scientists could tell a lot from the remains, and often could piece together a story of the bird’s life and death.
Katzner explained: “If you look at a radiograph of a bird, and it was hit by a single projectile weapon,” like a shot from a rifle or pistol, “there will be bullet fragments (of) all different sizes and shapes.”
But Thomason said “with a shotgun,” many pellets are encased in a shell that shatters on impact. In the X-ray of a bald eagle, researchers could see several pellets similar in size and shape, indicating “this was probably one shotgun shell (and) only a fraction of those pellets ended up in that bird. A lot of the pellets ended up somewhere else.”
Unsafe and costly, for both birds and humans
These shootings can have important implications for public safety, Thomason and Katzner said.
“From a societal standpoint, if people are shooting birds that are perched on power poles, they’re not shooting into a backstop. They’re shooting into the air, and they’re shooting towards electric, energized equipment,” Thomason said, noting that this runs the risk of creating sparks that could cause power outages or even wildfires.
“They say (in hunter safety classes) that a rifle bullet can travel a mile through the air,” Katzner pointed out, indicating the danger of a inaccurate shot.
“So that also makes fieldwork pretty interesting,” Thomason said, almost joking about the danger.
Beyond the safety and societal costs, there are economic costs that “get passed down the line,” according to Thomason.
When a bird is found along a power line and it’s assumed to have died from electrocution, “often these utilities are really good about going out and doing retrofits, making those poles safer (and) taking the time to restore energy or electricity to the surrounding areas,” Thomason said. “Oftentimes these costs are reflected in our power bills each month.”
Potential reasons for raptor persecution
Human activity has contributed to the loss of 3 billions birds across North America, according to an article in the journal Science a few years ago.
Research published in 2022 in an Ecological Society of America journal uncovered that shooting was probably the leading cause of anthropogenic fatalities in golden eagles.
“Golden eagle populations are held back by people. And that’s just an indicator that this could be the case for other species as well,” Katzner said.
The team’s count of dead birds painted a grim picture for golden eagles in particular.
“Golden eagles are pretty rare on the landscape,” Katzner said. Typically, “bigger birds are less common on the landscape.”
But despite their scarcity in that setting — or maybe because of it — golden eagles were the third-most common species that the team found along the power lines.
Are people shooting golden eagles as trophy animals?
In general, why would people shoot at birds on power lines?
When lawbreakers have been caught, “sometimes this is just something to do for fun, like a hobby,” said Thomason. Other times, people might want to protect their livestock and game animals. Thomason also noted that the wildlife trade is “a very prosperous criminal enterprise,” so that’s also a possibility.
But the answer isn’t a simple one, and the authors of this study hinted at future publications that feature more about the sociology of raptor targeting.
It’s clear that electrocution has been a scapegoat as the leading cause of bird deaths along power lines, and challenging that assumption, the researchers said, provides the first step toward a fuller, more accurate ecological picture.
