SALT LAKE CITY — Bald eagles are dying in Utah — 20 in the past few weeks alone — and nobody can figure out why.
Hundreds of the majestic birds — many with wing spans of 7 feet or more — migrate here each winter, gathering along the Great Salt Lake and feasting on carp and other fish that swim in the nearby freshwater bays.
This month, however, hunters and farmers across five counties in northern and central Utah began finding the normally skittish raptors lying listless on the ground. Many suffered from seizures, head tremors and paralysis in the legs, feet and wings.
Many of the eagles were brought to the mammoth Wildlife Rehabilitation Center of Northern Utah, where Buz Marthaler — a longtime animal caretaker — and other handlers tried to save the birds. Within 48 hours most were dead.
"It's just hard to have your national bird in your arms, going through seizures in a way it can't control — when you can see its pain but don't know what's happening to it," said Marthaler, 56, co-founder of the facility in Ogden.
State wildlife specialists are also baffled. For weeks, officials have sent birds for necropsies at the National Wildlife Health Center in Madison, Wis., hoping the results would offer clues.
They began to rule out obvious possibilities: The birds were not shot by hunters, and officials don't believe the birds were poisoned. "There doesn't seem to be anything suspicious in that regard," said Mitch Lane, a conservation officer with the Utah Division of Wildlife Resources.
At first, the agency's disease scientists guessed that the illness could be encephalitis, which is caused by the West Nile virus, but later ruled out that possibility. And although many sick eagles tested positive for lead, researchers did not think that it was killing the birds.
Officials suggest the eagle die-off is possibly connected to the deaths of thousands of eared grebes that began in Utah in November. Eagles are known to prey on the small shore birds. Because the grebes are thought to have died from avian cholera, many scientists theorize that the eagles became sick from feeding on infected grebes. Officials still don't know why the shore birds became sick.
"We're getting closer to an answer," Lane said, adding that officials would meet this week to continue investigating the mystery.