Testing from the National Wildlife Health Center has confirmed that dead grebes in Utah had West Nile virus — which spread to scavenging bald eagles, killing more than 50.
The center confirmed in December that the virus was behind sick and dead eagles that began appearing in northern Utah earlier that month. Wildlife officials came to suspect the migrating eared grebes, which gather on the Great Salt Lake in massive numbers each fall before continuing south.
As is common, up to 20,000 grebes died this year, and officials believed eagles feasted on infected birds.
Follow-up testing on dead Utah grebes showed they were positive for the virus and negative for lead, avian influenza and other possible causes of death, the center said in a bulletin released Friday. This is the first time the virus has been seen in eared grebes, it noted.
The eagle death toll has reached 54, with four live birds in rehabilitation, according to Leslie McFarlane, wildlife disease specialist for the Utah Division of Wildlife Resources (DWR).
Grebes have since migrated out of the state, and reports of sick eagles have "dramatically decreased," McFarlane said in an email Friday. However, the number of eagle carcasses being found is increasing, a trend that may continue as snow melts, she noted.
Utah has a small population of resident bald eagles, but the numbers are bolstered by up to 1,200 migrating eagles during some winters. DWR is going ahead with its popular annual Bald Eagle Day on Feb. 8, and will take the opportunity to discuss the outbreak with the public.
West Nile virus, spread by mosquitoes, has rarely been seen so late in the year and rarely seen in bald eagles. Before the Utah outbreak, the wildlife health center had tested 386 bald eagles for the virus and only 11 were positive, it said in the bulletin.
Based on the Utah findings, the virus should be considered a potential diagnosis throughout the year, the center said. The virus has been reported in more than 300 species of birds since it was first identified in the United States in 1999.
Since mosquitoes are not active, health officials say humans and livestock are not at risk. Still, wildlife officials encourage people not to touch sick or dead birds. Instead, call the nearest DWR office in Ogden, Vernal, Springville, Cedar City or Price with the animal’s location. The Help Stop Poaching Hotline, 1-800-662-3337, is another option on weekends and holidays and after hours.
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