Lab results link West Nile with eagle deaths
The puzzle of what killed 27 bald eagles in Utah over the past few weeks may have been solved.
Laboratory results from Utah Veterinary Diagnostic Laboratory in Logan, Utah, and the National Wildlife Health Center in Madison, Wis., have confirmed what officials with the Utah Division of Wildlife Resources have been suspecting: the bald eagles were killed by West Nile virus.
Wildlife officials think the birds might have contracted the virus, which normally affects birds during warmer months, after eating infected Western Eared Grebes that died recently on Great Salt Lake.
Leslie McFarlane, wildlife disease coordinator for the Utah Division of Wildlife Resources, said more than 2 million eared grebes stop at Great Salt Lake during their winter migration.
Almost every year, said McFarlane, about 1 percent of the grebe population that visits the lake dies from a bacterial disease called avian cholera.
“Every time grebes die,” she said, “we send some of the dead birds to a laboratory for testing. Usually, avian cholera jumps out as the cause of death.”
However, this year initial laboratory results were not as conclusive, McFarlane said.
“That led us to believe that something else might have killed the grebes this year,” she said.
Additional testing on the eared grebes, however, have led to findings that are consistent with what’s being found in the bald eagles.
Because wintering bald eagles obtain most of their food by eating dead animals, and all of the eagles that have died have been within flying distance of the lake, McFarlane thinks the eagles might have contracted West Nile virus after eating virus-infected grebes.
The laboratory testing ruled out many other possible causes of death, including toxic chemicals or poisons, lead poisoning, bacterial infections and several other viruses, including avian influenza and avian vacuolar myelinopathy.
McFarlane says between 750 and 1,200 bald eagles visit Utah in the winter. As of Dec. 31, 27 eagles had died in Utah. Twenty-one of those birds were found dead in the wild and an additional six died while being treated at rehabilitation centers.
JoDee Baker, epidemiologist with the Utah Department of Health, says people do not need to be concerned; dead grebes and dead eagles do not pose a risk to people.
“People become infected with West Nile virus after being bitten by a mosquito that carries the virus,” Baker said. “Although there are other very rare ways you can get the virus, such as receiving contaminated blood or organs from an infected person, mosquitoes are, by far, the most common method of transmission.”
Since the mosquitoes that transmit West Nile virus aren’t active in the winter, there’s no risk to the public’s health, Baker said.
McFarlane said the migration of eared grebes through Utah is almost over for the winter.
“By the second week of January,” she said, “almost all of the grebes will be gone.”
West Nile virus can live for a few days in the carcass of a bird that has just died, however, so there still is the chance that more eagles will sicken and die, even after the grebes leave.
But the risk to eagles should decrease quickly.
Five eagles still remain in the rehabilitation centers.
Officials from Colorado Parks and Wildlife said the state hasn’t seen anything similar to the Utah incidents.
“Our bald eagle populations tend to be more dispersed along the state’s rivers and not congregating in one place, as they do around the Great Salt Lake in Utah,” said Parks and Wildlife spokesperson Randy Hampton. “We’re aware of the problems in Utah but nothing has been reported in Colorado.”