The bald eagle was found in a ditch along a road near Orofino, Idaho, in late January, and was unable to stand, said Nickol Finch, head of the exotics and wildlife unit at WSU's veterinary teaching hospital in Pullman.
Finch named the bird Sauder, after the Idaho fish and game biologist who rescued him. The bird was given intravenous fluids and chelation therapy, which binds the lead so it can be eliminated through the kidneys.
The eagle improved enough to be released on Monday near where he was found.
"He's one of the lucky ones," said Finch, who noted that a golden eagle with lead poisoning had died a few days before at the hospital.
Scientists theorize that eagles get exposed to lead by eating from the carcasses of animals that have been shot or eating fish that contain lead fishing weights, Finch said.
Numerous scientific studies, including one at WSU that spanned 18 years, show that lead shot and bullet fragments in animal carcasses can be ingested and lead to poisoning in birds, Finch said.
In addition to acute poisonings, lead exposure in wildlife can cause chronic symptoms of illness. For instance, Finch said eagles can grow thin, struggle to lift their wings, collide with cars and even become prey themselves.
"We almost always get lead-poisoned birds between the months of November and late February," she said, because eagles at those times are feeding on the remains of large animals shot by hunters.
"In most cases, we'll treat them for lead poisoning, regardless of the symptoms," Finch said. "The lead may have made an eagle too weak to move out of the way of a moving car and so it gets hit. We try to cover all the bases."
The notion of bullet-caused lead poisoning is controversial, as some hunting groups contend the problem is not widespread.
In 1991, the federal government banned the use of lead shot in waterfowl hunting across the nation. In 2007, California prohibited lead bullets in parts of the state where the endangered California condor lives.