DULUTH — The local weather radar turned into a feather radar for a few hours Wednesday morning.

Meteorologists in the National Weather Service’s Duluth office noticed some unusual activity on the screen and became worried there was a fire in Aitkin County.

They called the sheriff and the fire center, and no one had heard of any emergencies. Then they rang up the Rice Lake National Wildlife Refuge, where the action seemed to be concentrated.

It turned out to be 600,000 ducks.

Kevin Huyck, a meteorologist, said workers from the refuge said they’d been out conducting a waterfowl survey in the morning from about 10 a.m. to 11:30 a.m. The timing corresponded almost exactly with what had appeared on the radar in Duluth.

The surveyors went out onto the lake in airboats, which likely disturbed the ducks on the lake, Huyck said. They flapped around until the vessel left and the birds could settle peacefully on the water once again.

Huyck said meteorologists were surprised by the size and timing of the echo the ducks caused. The weather service is used to its radar picking up “roosting rings” from time to time, but that usually happens around sunrise in autumn or spring, when birds are on their migratory paths.

“Nearest we can figure is there’s something special about that lake in particular,” Huyck said. “The highest duck counts in the region tend to come from that site. There must be something that the ducks especially like.”