This bird gave me some problems with id so I thought I'd share how I came to this conclusion. Trumpeters are trying to be reintroduced in Iowa so an unmarked bird could be fairly interesting whereas Tundras are not that unusual. It seems like this id problem comes up fairly frequently. At first this bird looked like a Trumpeter to me because the upper mandible looked fairly straight and I wasn't seeing any yellow in the lores. The clincher for me and this hasn't been a field mark I've been paying much attention to was the irregular feather line where the bill meets the face which should be a straighter edge on the Trumpeters like the lower red line I put in the second photo. Also between the 2 red lines there does seem to be a touch of yellow. The top red line is supposed to show that if the upper mandible was really straight it wouldn't cut off much of the head. The upper mandible does seem to have some curve near the base. Also the lores seem slightly pinched.