For the most part, turkeys weren't introduced where they'd never been historically. They were reintroduced where they had been historically, but in some cases have spread out into areas where they hadn't been before.
Biologists made some bad assumptions about turkeys. When they were reintroduced in Iowa and had become numerous enough to support a hunting season, the DNR biologist told me we'd probably never kill more than 1,000 of them in a season. That was based on the fact that Iowa doesn't have a whole lot of forest, and on how much mast turkeys need to eat in order to survive. While those assumptions likely worked historically, they fell apart when the birds were brought into a very agricultural state where they had no shortage of high quality food other than the nuts, berries etc they could eat in the woods: CORN. It wasn't long at all before Iowa turkey hunters left the 1,000 bird harvest in the rear view mirror. What Iowa has is unusually high densities of turkeys where there are woodlands, because of all the food provided to them by the farmers.
