Birds get electrocuted on power lines. But people shooting at birds perched on power poles may be even more of a problem. In a survey of five sites in the western United States, two-thirds of birds found dead beneath power lines had been shot.
Avians found dead along power lines are often assumed to have died from electrocution, especially if their bodies show burns or singeing, said Eve Thomason, a wildlife biologist at Boise State University in Idaho. But the animal may have been injured or killed before getting zapped.
“We really need X-rays to understand fully what may have happened,” said Ms. Thomason, who used to work for a utility surveying power lines to assess the risk they posed to birds.
In the new study, published Tuesday in the journal iScience, Ms. Thomason and her colleagues walked along 122 miles of power lines in Idaho, Oregon, Utah and Wyoming, collecting 410 bird carcasses. Back in the lab, the researchers X-rayed the birds, looking for evidence of gunshot wounds or other trauma.
“Most of them were coming back with bullet fragments in them or shotgun pellets,” Ms. Thomason said. Of the 175 birds for which they determined a cause of death, 66 percent had been shot, the scientists reported.
There have been anecdotal reports of such shootings. But “this is the first time somebody has done a large-scale study at multiple sites to figure out if this is a problem,” said Todd Katzner, a research wildlife biologist at the United States Geological Survey in Boise and one of the study’s authors. “This is way more prevalent than we had previously understood,” he said.
The sites vary in proportion of birds shot, said Libby Mojica, a wildlife biologist and ornithologist at the engineering firm EDM International who was not part of the study. At two sites, all deaths were attributed to gunshots. But at another, shootings accounted for 39 percent of deaths and a similar percentage of deaths were from electrocution. It’s not clear how widely applicable the findings are, but even the lowest percentage makes for a large number of birds, she said.
The dead birds were mostly ravens and raptors, the group that includes eagles, hawks and falcons. Killing these animals is illegal under several U.S. laws. And shootings, including those at power lines, may be placing populations of some birds, such as golden eagles, in danger.
Illegal shootings are “an overriding issue that just perplexes the heck out of me,” said Brian Millsap, an ornithologist at New Mexico State University. Dr. Millsap wasn’t part of this study, but he has collaborated with Dr. Katzner. “There’s just been a ton of work done to get the word out that raptors aren’t the vermin that they were thought to be,” he said.
With all the effort that state fish and wildlife agencies, nongovernmental organizations and the U.S. Fish and Wildlife service have put into educational campaigns, researchers had assumed that shootings had declined.
Electrical utilities that own the power poles are liable for bird deaths from their infrastructure, Ms. Mojica said. Some large electrical utilities spend hundreds of thousands of dollars per year to reduce the risk of avian electrocutions. But if birds are dying because of crimes, that shifts the blame away from power companies and may mean different conservation actions are needed, she said.
Still, electrocutions remain a problem at power poles in some places, Dr. Millsap noted. Recent work that he and his colleagues have yet to publish found that, in parts of Texas and New Mexico, some 34 percent of golden eagles that survive to leave their nests are electrocuted within their first year of life, he said. That is occurring in places where utilities haven’t prioritized retrofitting poles to make them raptor safe.
The researchers are extending their study into Nevada and working to understand what motivates people to shoot at protected birds. But preventing illegal kills is challenging, Dr. Millsap said. Enforcement and prosecution takes time, and the strategy can be undercut by judges who issue low fines.
Nonetheless, Pete Marra, an ornithologist at Georgetown University who has studied the decline of North American bird populations but wasn’t a part of this study, said the work was important in fighting bird extinctions. “What’s essential in order to stop the declines of birds is to understand what’s causing the declines of birds,” he said.