A fungal infection is to blame for the death of 2,500 mallard ducks southeast of Burley last week, according to the Idaho Department of Fish and Game.
A hunter first discovered a handful of dead ducks along Land Creek Springs near Oakley on Dec. 8. Fish and Game officers investigated the report and found about 10 dead ducks. By Dec. 10, that number climbed to 500 and about 2,500 had perished by Dec. 14.
The infection was limited to mallard ducks, according to Kelton Hatch, conservation educator for Fish and Game's Magic Valley Region. Eagles, hawks, crows, coyotes, and fox were all seen feeding on the carcasses of the dead mallards, and none appeared to be affected, he said.
The mysterious and massive die-off spurred a joint investigation by Fish and Game, the Bureau of Homeland Security, Department of Environmental Quality, U.S. Fish and Wildlife Service, Department of Agriculture and South Central Health District.
Avian influenza, which was considered an unlikely cause of death from the beginning, was officially ruled out late last week.
Test results from the University of Idaho confirmed the ducks had contracted acute aspergillosis, a respiratory tract infection caused by fungus found in soil, dead leaves, moldy grain and other decaying vegetation. Moldy grain is the most likely source of the fungus, according to Fish and Game, but no specific site has been identified.
Hatch said the infection is waning and will likely not spread to other areas.
"It seems to have really tapered off," Hatch said. "But we're still waiting for some other tests to come back to make sure that this is just a one-time episode."
According Fish and Game, waterfowl die-offs are common—16 events involving more than 1,000 birds have occurred in the United States in the past year. But Dave Parrish, supervisor of Fish and Game's Magic Valley Region, said he's never heard of an event this large.
While the infection took a toll on the local duck population, Parrish said it will not impact regional populations.
People who encounter other dead or sickly birds are encouraged to contact Fish and Game at (208) 324-4359.
