Two years ago, was with a tour group, and we spotted a Common Crane in with the Sandhills. Turns out the bird had been seen 8 years before we had seen it, but had not been seen for 2. The speculation is that this bird had joined the Sandhills somewhere in Siberian breeding grounds, where the two species overlap. You can clearly pick it out here in this group. Apparently, only a couple of dozen sightings of a Common Crane have been recorded in North America.
And then there was the Whooping Crane juvenile who we spotted last year. It had joined up with Sandhills. you can still see some orange plumage to show that it was not quite yet a year old.