Since December 1, 27 bald eagles have died in northern and central Utah. The birds all had similar symptoms: head tremors, signs of seizures, weakness in the legs and feet and paralysis of the wings.
For weeks, scientists weren't able to figure out what was killing the raptors, but now lab results have turned up some answers.
"It was West Nile Virus," said Leslie McFarlane, wildlife disease coordinator with the Utah Division of Wildlife Resources. "We believe we had another bird that started dying a little sooner than December, it's called an eared grebes...we believe that the eagles are feeding on these birds after they've died or as they're dying and that they're becoming infected with West Nile."
Scientists notices the symptoms as being similar to West Nile, but the lack of mosquitos in the area delayed the diagnosis. The deaths don't post a threat to human populations.
"Typically you have mosquitos that have to be the one to pass West Nile Virus from animal to animal or animal to people," said McFarlane. "We're freezing here, so we don't have a lot of mosquito activity so that's why we took a really hard look at this."
Preventing the spread of the illness is difficult, because some birds can act as carriers of the virus. When the infected grebes die, bald eagles — who tend to be prolific scavengers — will eat the birds and become infected. MacFarlane says her team will continue to monitor the birds and treat those they find ailing from the illness.