Lab results confirm cause of eagle deaths: West Nile
Laboratory results have confirmed what officials with the Utah Division of Wildlife Resources have been suspecting: West Nile virus killed the bald eagles that have died in Utah over the past few weeks.
Testing at the Utah Veterinary Diagnostic Laboratory in Logan, Utah, and the National Wildlife Health Center in Madison, Wisconsin, has definitively 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.
Officials aren't certain how the eagles got West Nile virus, as the disease typically affects birds (including eagles) during warmer months, when mosquitoes that carry the disease are active.
They think the birds might have contracted the virus after eating infected eared grebes that died recently on Great Salt Lake.
Leslie McFarlane, wildlife disease coordinator for the Utah Division of Wildlife Resources (DWR), says more than 2 million eared grebes stop at Great Salt Lake during their winter migration. Almost every year, about one percent of the population that visits the lake dies from a bacterial disease called avian cholera.
"Every time grebes die," she says, "we send some of the dead birds to a laboratory for testing. Usually, avian cholera jumps out as the cause of death. This year, though, the initial laboratory results were not as conclusive. That led us to believe that something else might have killed the grebes this year."
Additional testing on the eared grebes, however, have led to findings that are consistent with what's being found in the bald eagles.
In the winter, bald eagles obtain most of their food by eating dead animals. Since 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 grebes that died at the lake from the disease.
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.