The Christian Science Monitor has an interesting article about the USDA's "Bye Bye Blackbird" program that was started in the 1960s to kill birds on behalf of farmers. While the agency denies any role in the mass deaths in Louisiana and Arkansas, it did admit to using a poison to kill 5,000 birds that died in South Dakota. The birds were apparently defecating in a farmer's cattle feed across state lines in Nebraska.
The article also links to a chart that lists the number of animals that were taken by the USDA in 2009. In 2009 alone more than 4 million red-winged blackbirds, starlings, cowbirds, and grackles were killed. Moreover, the U.S. Fish and Wildlife Service allows blackbirds, starlings, and grackles to be killed under so-called depredation orders. These killings are undertaken by private contractors that do not need to report the culls to any authority.