SIOUX CITY, Iowa (AP) — Hundreds of ducks and other migratory waterfowl have been hit and killed by cars in northwestern Iowa after they mistook wet pavement for wetlands, wildlife officials said.

State conservation officer Steve Griebel, with the Iowa Department of Natural Resources, said he began receiving phone calls and texts about ducks on roads and parking lots in Woodbury County starting around 9:30 p.m. Monday and into early Tuesday. He went to investigate after sunrise, taking Highway 20 east of Sioux City.

“I counted over 200 dead ducks on the highway, and can only imagine how many dead ones were out of sight in the ditch,” Griebel said in a news release. “It was all different species — mostly bluebills, but there were mallards, buffleheads, teal. It must have been an epic migration.”

The waterfowl were migrating south from colder climes in the Dakotas and Canada, according to the department.

Migratory waterfowl tend to migrate at night, state waterfowl biologist Orrin Jones said. The birds likely left when the weather was clear before they met a strong weather front and freezing rain that forced them to set down in Woodbury County, he said.