In the Great Basin of the western U.S., power poles and power lines are often the tallest landscape features available to birds for perching and nesting. However, these human-made structures can also come with risks to birds.
“Power-line collisions and electrocutions are well documented causes of bird deaths worldwide, but there are many other risks to birds that live near humans. An accurate diagnosis is essential for effective wildlife management,” said Eve Thomason, lead author and a recent graduate of the Raptor Biology MS program and now a Research Associate in the Raptor Research Center at Boise State University. “Knowing if a bird died from electrocution, fell from a nest, was shot, or even exposed to poison, is critical to guiding conservation decision-making.”
The goal of the study was to test the common assumption that electrocution is the greatest threat to birds along power lines. 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. To understand cause of death, each bird carcass was inspected for visible injuries, photographed, and then transported to the Idaho Department of Fish and Game Wildlife Health and Forensic Lab for a full examination and x-rays.
The team was able to determine the cause of death for 175 of those birds, of which 66% died from gunshot. Many of the birds shot were species protected by state and federal laws, including bald eagles, golden eagles, and several species of hawks. As such, these shootings were illegal. By comparison, death by electrocution and collisions were split almost evenly at around 17% of each.
“These results demonstrate that illegal shooting of birds along power lines is much more common and a more significant threat to bird conservation than we thought,” said co-author Todd Katzner, U.S. Geological Survey Supervisory Research Wildlife Biologist and Thomason’s graduate advisor. “Death by shooting has been shown to impact population growth of some species, including golden eagles, but we didn’t know it is relevant to so many species across a such a large geographic area.”
Several birds had visible signs of electrocution, including burns and singed feathers, but x-rays revealed that they had also been shot. One bald eagle collected in southeast Oregon had such convincing external signs of electrocution that the utility company implemented on-site mitigation measures to reduce future risk to birds at that site. X-rays later revealed numerous shotgun pellets throughout the eagle’s body.
“This study is unique because we x-rayed the remains of every bird we found. All that work paid off, as we found things that would have been missed with just external examinations,” said Thomason. “We suspect that in this case, this eagle was shot and contacted power lines as it fell to the ground.”
“Utilities have focused efforts on reducing electrocution and collision along power lines for decades. The results of this study show that shooting is another conservation challenge for raptors that needs to be addressed,” added Natalie Turley, Idaho Power biologist and co-author.
The paper, “Illegal shooting is now a leading cause of death of birds along power lines in the western USA,” was published in the journal iScience.
Funding for this study was provided by the Idaho Army National Guard, Avian Power Line Interaction Committee, U.S. Fish and Wildlife Service, Bureau of Land Management, the Raptor Research Center at Boise State University, and U.S. Geological Survey.
Idaho Power provided access to powerlines in areas bird fatalities have occurred. The Idaho Department of Fish and Game Wildlife Health and Forensic Laboratory provided training, supervision, consultation, and facilities to perform examinations and x-rays. Law enforcement officers from the Idaho Department of Fish and Game, Bureau of Land Management, and U.S. Fish and Wildlife Service provided insight into illegal killing of wildlife and investigated some of the illegal shooting discovered during this study.