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.