Went to one of my snowy owl hotspots today-none there but found this guy trying to raid a pheasant farm. Photos taken in Howard County, IA. It was roughly red-tailed hawk size, possibly a touch bigger. Juvenile gyrfalcon maybe? Definitely has the falcon look to its head, but size and color don't seem right for a peregrine-and it's way too big to be a merlin.
Since posting this I have gotten emails from several IA birders(through another site) who agree it's a first-year dark morph gyrfalcon, and a few are on their way to the area hoping for photos of their own. Here's hoping they find it.