The first golden eagle marked and followed for research in Yellowstone National Park’s history lasted only about four months before a common human-caused source of death did the bird in.
The adult female, captured in August, was being studied by University of Montana graduate student David Haines. On Dec. 6, she turned up dead, discovered near Phantom Lake in Yellowstone’s Blacktail Plateau, said Todd Katzner, an adviser to the study and a research wildlife biologist for the U.S. Geological Survey’s Forest and Rangeland Ecosystem Science Center.
“The focus of the research is on local breeders and understanding their behaviors and the threats they face,” Katzner said. “We very quickly found out one of the threats they face.”
In recent years, Katzner said, wildlife scientists have enhanced their understanding of lead poisoning’s impact on eagles and other scavengers. It’s now known that hunter-killed carcasses are a chief cause of lead exposure and the reason for seasonal fluctuations in blood-lead levels in animals that scavenge carcasses, especially avian species.
Gut piles and carcasses left behind from late-season Montana elk hunts along Yellowstone’s northern boundary were likely a factor in the golden eagle’s death, Yellowstone officials wrote in a Monday press release.
“Transmitter data revealed that the eagle ranged extensively during the 2018 autumn hunting season north of the park before it died,” the statement said. “The lead levels in the marked eagle indicated it likely ate carrion that contained lead fragments.”
The research group Craighead Beringia South, based out of Kelly, is running a parallel study of Montana golden eagles and partnering on the park project, which now follows six tracked golden eagles.
Out of 30 golden eagles Beringia South has monitored over the years with GPS equipment, two have died from lead poisoning, research biologist Ross Crandall said.
“That’s two of five confirmed mortalities for our study,” Crandall said. “It’s substantial.”
The female golden found dead at Phantom Lake registered a 48 parts per million “dry weight” reading of lead in her liver. That’s “well over lethal toxicity,” according to Yellowstone’s statement, and compares to a natural level that would “probably” be below 5 parts per million, Crandall said.
Some land managers, like Grand Teton National Park, have required big game hunters to use nonlead ammunition to prevent lead poisoning of scavengers. Nationwide, lead is banned for waterfowl hunting to reduce its impacts on ducks and other bottom-feeding wildlife. California became the first state to ban lead ammo for all types of hunting.
More broad-based reforms have run into political opposition and failed. In early 2017, then-U.S. Fish and Wildlife Service Director Dan Ashe announced a complete ban on lead ammunition and fishing tackle on national wildlife refuges, which would have changed the rules on the National Elk Refuge, a major draw for scavenging bald eagles during late-fall hunts.
But when President Trump’s first interior secretary, Ryan Zinke, took over later that year he promptly reversed the policy change, permitting lead ammo.