It’s not the “aflockalyptic” fallout from a secret US weapon lab as some have theorized. But the government acknowledged Thursday that it had a hand in one of a string of mysterious mass bird deaths that have spooked residents in Arkansas, Louisiana, Alabama, South Dakota, and Kentucky in the last month.

The United States Department of Agriculture (USDA) took responsibility for hundreds of dead starlings that were found on the ground and frozen in trees in a Yankton, S.D., park on Monday.

The USDA’s Wildlife Services Program, which contracts with farmers for bird control, said it used an avicide poison called DRC-1339 to cull a roost of 5,000 birds that were defecating on a farmer’s cattle feed across the state line in Nebraska. But officials said the agency had nothing to do with large and dense recent bird kills in Arkansas and Louisiana.

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A Google map of mass animal deaths across the country

Nevertheless, the USDA’s role in the South Dakota bird deaths puts a focus on a little-known government bird-control program that began in the 1960s under the name of Bye Bye Blackbird, which eventually became part of the USDA and was housed in the late ’60s at a NASA facility. In 2009, USDA agents euthanized more than 4 million red-winged blackbirds, starlings, cowbirds, and grackles, primarily using pesticides that the government says are not harmful to pets or humans.