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Utah wildlife officials are scrambling to determine what led to the deaths of four bald eagles in northern Utah in the last week.

The eagles all appeared healthy, with the exception of head tremors. The raptors also displayed evidence of paralysis and digestive issues.

The birds were delivered to or picked up by officials from the Wildlife Rehabilitation Center of Northern Utah in Ogden and the Great Basin Wildlife Rescue in Mapleton.

The deaths are particularly troubling and mysterious because the birds were found in different locations — Corinne, Grantsville, Lehi and Weber County.

"It just rips your guts out. They are obviously suffering and you are helpless. It is so hard to watch," said DaLyn Erickson with the Wildlife Rehabilitation Center of Northern Utah. "Never in my career have I heard of four bald eagles in such a widespread area dying at the same time like this."

The first bald eagle arrived at the Ogden facility Dec. 1 from Weber County. Another eagle landed at the Mapleton rehabilitation center on Dec. 8. The last two arrived in Ogden this week.

All four displayed head tremors — uncontrolled shaking of the head; something that made Erickson suspicious of possible lead poisoning. But preliminary results from testing at the Utah Veterinary Diagnostic Laboratory in Logan, a cooperative lab with Utah State University and the Utah Department of Agriculture and Food, came back with unexpected results.

"There were no really elevated levels in any of the areas that would indicate lead poisoning," Erickson said. "If it had been, there were some things we could do about it."

Instead, Erickson and Patti Richards at the Great Basin center had to watch the symbols of the United States die.

Leslie McFarlane, wildlife disease coordinator with the Utah Division of Wildlife Resources (DWR), said recent necropsy results from the eagle with the blood results showed indications of encephalitis — swelling of the brain — which can be an indication of West Nile virus.

Another possibility is a more recent disease known as avian vacuolar myelinopathy, a neurological disease found in 1994 in the southern United States, impacting bald eagles and American coots.

McFarlane says it is late in the year for the appearance of West Nile, which is an insect-borne virus and more common in the summer months.

She is sending the Utah eagles to the National Wildlife Health Center in Madison, Wis., for testing. Results from the are likely at least two weeks away.

In the meantime, McFarlane asks people who observe distressed bald eagles to contact the local DWR offices (Ogden, Vernal, Springville, Cedar City and Price) with the location. She suggests using the Help Stop Poaching Hotline —1-800-662-3337 — on weekends and holidays.

"People shouldn't just go out and pick them up," she said. "They are wild animals and will defend themselves if they can. It's best to have wildlife specialists handle them."

Twitter: @BrettPrettyman