My late father was THE authority on Turkey hunting, but I never could get into it. I know one thing about Turkeys. Those birds have the sharpest eyesight you could possibly imagine!
A few years ago, I took a treeclimbing stand and my binoculars to a point along a powerline, for the sole purpose of observing deer. It wasn't "season" yet. I had paced off the distance between the power poles and knew each pole to be 150 yds apart. Using my binocs, I spotted a gobbler herding his hens in my general direction, not too long after sun up. They were over 600 yards away. About the same time I spotted the turkeys, I saw a small buck cross the powerline between me and the feeding birds. They, like me, stopped and watched the deer amble across the opening.
When the deer had gone I shifted my eyes back to the Tom and his harem. At this point they were approximately 500 yds from where I sat, fully camoflaged and sitting stock still. The old Tom was herding his brood in my direction, but to see them I had to keep the binoculars to my eyes.
Absently mindedly I reached up and scratched my back with my free hand while continuing to stare at the turkeys. I saw the "boss" immediately crane his neck and call a halt to his little friends. Incredibly he had spotted my slight movement from a distance of at least 450 yards! After a few moments, during which I didn't move an eyelash, the cagy old bird turned his flock around and headed back they way they came.
I was (and am still) amazed at the their visual acuity. So if you're gonna hunt 'em, you'd better have your ducks in a row.