Yellowstone National Park is famous for being a pristine haven in some of the most beautiful terrain in the western U.S., but it seems the park alone isn’t enough to protect the wildlife that call it home. A research team in Yellowstone has encountered a setback that underscores that issue: the untimely death of a golden eagle they were tracking. Officials confirmed this week that the first golden eagle fitted with a GPS tracking device had died from lead poisoning, likely after eating bullet fragments from an animal killed by a hunter outside the park, The Denver Post reports.
“It’s a little gut-wrenching because it’s so darn hard to trap and tag an eagle, and it’s frustrating for the graduate student who’s leading the project,” U.S. Geological Survey eagle scientist Todd Katzner told The Denver Post.
The bird was an adult female golden eagle, thought to be about five years old. She died in December, and officials have now released a probable cause of death following an examination of the bird’s remains. Researchers found that the bird had a level of lead well beyond the lethal limit, Atlas Obscura reports. Eagles often scavenge on the guts left behind when hunters field dress an animal. Eating those remains can expose the birds to fragments of lead bullets, causing lead poisoning.
“Avian scavengers globally are exposed to lead and suffer from lead poisoning,” Katzner told Atlas Obscura. “Data show that lead levels in birds usually peak during winter—concurrent with timing of hunting seasons. As such, it is not a surprise that a bird that crosses in and out of Yellowstone may have been exposed to lead.”
Researchers have managed to trap and tag several other Yellowstone golden eagles, but it’s a difficult process, so losing one is a major blow to their research efforts. The tracked birds are fitted small, backpack-like GPS devices that ping the animal’s location every hour. Golden eagles are one of the largest birds in North America, with a wingspan of about seven feet. While their numbers are steady, they’re lower than they could be, and the birds have an alarmingly low birth rate. The tracking project was devised to help wildlife researchers figure out why.
Although the female raptor was killed just four months after she was fitted with a tracker, she did provide valuable information for researchers: She ranged nearly 40 miles outside her home turf in Yellowstone during that time. Her death illustrates the complex array of threats that wildlife face, even when land is set aside to protect them. Some activists have called for bans on lead bullets (California has passed a ban that goes into effect on July 1) to protect birds and other animals that scavenge on remains. Copper bullets are an alternative, but they’re more expensive. Regardless, the eagle’s death shows that even legal hunting can have negative effects for wildlife.
“As researchers, it is always frustrating when this happens,” Katzner told Atlas Obscura. “We care about the animals we study and we care about the success of our research.”