BOISE, Idaho – A bacterial or fungal infection might have caused as many as 2,500 mallard ducks to die in a bizarre cluster along an Idaho creek bed, a state game official said late Thursday.
Preliminary test results suggested the possibility of infection, but more tests are planned on water and grain in the area, said David Parrish, supervisor for the Magic Valley region of the Idaho Department of Fish and Game.
Idaho and federal officials, including a representative of the Homeland Security Department, conferred by conference call late Thursday.
• Click here to visit FOXNews.com's Natural Science Center.
Parrish declined to say specifically what was discussed, but didn't rule out the possibility that more ducks might die in the area.
"We may have a few more, but that's a little difficult to predict right now until we can determine the exact cause of the mortality," he said.
He said the die-off was not typical.
"It's fairly uncommon, especially in these types of numbers and in such a confined area," he said.
The battery of tests were being performed at the U.S. Fish and Wildlife Service's national laboratory in Wisconsin, the University of Idaho and Washington State University.
The ducks mysteriously began dying last week around Land Springs Creek, near the remote town of Oakley, about 180 miles southeast of Boise.
Migratory mallards from Canada and their local cousins staggered and struggled to breathe before collapsing, Parrish said. He said every mallard in a radius of several miles has died — approximately 2,500, up from an earlier estimate of 1,000.
"I've never seen anything like this in 20 years here," he said. "There were dead mallards everywhere — in the water and on the banks. It was odd, they were in a very small area."
The outbreak is vexing scientists because only mallard ducks are dying. Golden eagles, geese, magpies, crows and other birds in the area all remain healthy.
Mark Drew, a wildlife veterinarian with the state Department of Agriculture, said earlier that investigators were not ruling out any cause of death, but bird flu virus remained unlikely.
The symptoms — bacterial lesions in the lungs and hemorrhaging in the heart wall — probably point to a bacterial infection, he said.
The ducks may have contracted a bacterial or fungal infection by eating grain treated with pesticides by local cattle farmers, Drew said.
Farming chemicals might also have spilled into the small spring-fed creek, which measures just 3- to 6-inches deep.
The agencies posted signs warning hunters not to eat any birds killed near the creek.