Here is a record shot of a putative Thayer's that I noted 40 minutes out of Castlebay, Barra en route to Lochboisdale. I picked up the bird solely due to the fact that it was being chased by a bonxie. It was only then that the dark 'Iceland type' plumage became apparent, but was evidently veering beyond Kumlien's into Thayer's territory. From below and against the light, but check outer Ps with dark trailing fringe. This photo has done the rounds with positive response and I thought to put it on in light of the Dunbeg bird.