Inhabitants in Yankton were surprised when they found hundreds of starlings lying frozen on the streets and in the city's Riverside Park, MSNBC reported. Some people thought the birds had simply left it too late to fly south for the winter.
Now, the USDA says it set out poisoned bait for the birds after a local farmer complained that they were defecating in his animal feed.
"They say that they had poisoned the birds about 10 miles south of Yankton, and they were surprised they came to Yankton like they did and died in our park," says Yankton Animal Control Officer Lisa Brasel.
There has been a string of mass animal deaths so far this year, from dead fish in the Detroit River to red-winged blackbirds falling from the sky in Arkansas and Louisiana.
In Yankton, the starlings made the area look like something out of an Alfred Hitchcock movie, witness Alison Brown said.
The USDA says the dead birds do not pose a threat to any animal that might eat them, such as house cats.
The agency does not typically poison animals, but felt it made sense in this case, USDA biologist Ricky Woods said, according to Reuters.
"Lethal means are always a last resort," Woods said. "In this situation it's what we had to do."