The Minnesota Department of Natural Resources is blaming a large bird die-off in western Minnesota on Newcastle disease, a viral disease that commonly infects cormorants.

As of earlier this week, about 500 cormorants and 400 ring-billed gulls had been found dead on Marsh Lake near Appleton in Big Stone County.

Erika Butler, a wildlife veterinarian for the Minnesota DNR, said the birds died from what's known as Newcastle Disease, which causes partial or complete paralysis in water fowl.

"One of our biologists was out banding birds noticed some increased mortality in some double-crested cormorants," Butler said. "So at that time we collected some carcasses and submitted them to the National Wildlife Health Center in Madison, Wisconsin for some testing. We got the results back that indicate that we're dealing with a Newcastle disease outbreak."

DNR officials will try to determine which strain of Newcastle Disease infected the birds. Avian influenza tests were negative, officials said.

Newcastle Disease commonly infects cormorants, but gulls and pelicans can also get it. Signs include a droopy head or twisted neck, lack of coordination and inability to fly. Juvenile birds are more likely to be affected. Butler said workers are disposing of carcasses to limit the spread of the disease. "We remove any sick birds as well," she said.. "So it's kind of going to be ongoing effort, and we're also checking other rookeries throughout the state."

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The last Newcastle Disease outbreak in Minnesota happened in a seven-county area in 2008 when about 2,400 birds died.

DNR officials are also investigating the deaths of 50 cormorants on Wells Lake in southern Minnesota's Rice County.

Newcastle Disease does not affect humans, but the DNR said poultry farmers should watch for clinical signs of the disease in their flocks.

(MPR reporter Mark Steil reported from Worthington, Minn.)