The Main Thing Killing Birds Near Power Lines Isn't Electrocution

In an oft-cited study published in 2019, a team of researchers reported net population losses of some three billion birds across North America since 1970. Calling it a “staggering decline of bird populations,” the researchers cited “habitat loss, climate change, unregulated harvest, and other forms of human-caused mortality” as the causes of this biodiversity crisis.

Those other forms of “human-caused mortality” are grim and frustratingly senseless. Up to three billion birds a year die from outdoor cats, and another one billion from colliding with glass. (Despite the narrative of fossil-fuel-aligned pundits, wind turbines account for deaths in the hundreds of thousands each year—which is still way too many, but it is not the leading cause of death, by far.)

Another one of those anthropogenic causes is power lines. Bird enthusiasts and rehabilitators are all too familiar with finding dead birds near power lines—as are the utility companies. 

But now, a new study finds that the leading cause of death of birds near power lines is not electrocution, but illegal shooting. And federally protected species like eagles, hawks, and ravens are taking the biggest hit.

A Surprising Discovery

Birds are drawn to power lines and poles for perching and nesting—but can be electrocuted if they come into contact with two energized parts of a power line at the same time. This can occur, for example, when they spread their wings to take off from or land on a power pole. Since these bleak events can cause power outages and spark wildfires, utility companies actually spend ample time and money mitigating the threat by modifying structures and line configurations, insulating energized equipment, installing flight diverters, and installing safe perches and nest platforms.

It is generally assumed that when a dead bird is found by a power line, it died from electrocution.  But prior to the study, when Eve Thomason, a research associate at Boise State University's Raptor Research Center, was doing avian risk assessment for a power company, she kept finding dead birds along power lines that should have been avian-safe.

When she realized many were being shot, she organized the research project. 

"Solving conservation problems only works when we can accurately identify the cause of those problems," says Thomason, first author of the study. "In this case, we need to know how birds are dying along power lines so that we can come up with strategies to reduce bird deaths."

Federally Protected Bird Are Being Shot

By foot and car, the team repeatedly surveyed 122 miles (196 kilometers) of power lines in Wyoming, Idaho, Utah, and Oregon in search of dead birds. Between 2019 and 2022, they found 410 dead birds from more than 48 species—among those were 185 raptors and 132 corvids.

They then took them back to a lab to determine each bird's cause of death. Of the 175 birds for which they could determine a cause of death, 66% died from gunshot.

Even birds that may appear to have been electrocuted were found to be shot. In one example (photo below), a power company initially diagnosed the cause of death of a bald eagle as electrocution—a sensible assumption given the singed feathers and wings. The power company spent a substantial amount on mitigation to reduce the future risk of collision and electrocution at the site. 

“However, our radiographs revealed numerous pellets that were associated with fresh injuries and entrance wounds,” the authors write in the study. “These observations suggest that the bird died from gunshot before contacting the power lines as it fell to the ground and thus that the mitigative actions taken were misplaced. Together, these patterns highlight the importance of detailed laboratory examinations, including radiographs, of all avian carcasses when attempting to diagnose possible CODs [causes of death] of birds found along power lines.”

Relevance for Conservation

While extra avian-proofing is not a bad thing, obviously, the incorrect diagnosis of cause of death of birds impacts law enforcement and management. And as the authors point out, addressing illegal shooting may have great relevance for avian conservation.

"What's unique to our study is that all remains were documented, collected, and X-rayed. We tried to identify the cause of death for every bird we found," says Thomason. "Prior studies typically only documented birds that were in relatively good condition, and X-rays were only sometimes performed."

The researchers are planning to continue their power line surveys and expand into new areas so they can understand the extent of illegal shootings and the reason why birds are being shot. They hope to provide information for law enforcement as they plan patrols or investigations to prevent this illegal shooting from continuing.

"We are just beginning to understand this problem, and in a lot of cases, it's really difficult to know what's going on," says Thomason. "Here's what the research tells us: when people have been caught doing this activity, we've learned that sometimes people shoot protected birds for fun, and sometimes they're trying to protect their livestock from predators."

“Our work suggests that, although electrocution and collision remain important,” the authors conclude, “addressing illegal shooting now may have greater relevance for avian conservation.”

The study, Illegal shooting is now a leading cause of death of birds along power lines in the western USA, was published in iScience.