A possible Gaelic meaning for Maes is 'buttock' with no takers.
Peace or war 'twixt Vikings and Picts here. I think I buy into the Celtic populace having died out just before the Vikings moved in. But they could well have had battles in the Orkney Isles before this happened. Visiting Norsemen could well explain the small minority of probable Celtic placenames hereabouts that Marwick noted. As for P- or Q-Celt there is also the contact outwith these islands that led to Viking stock becoming the Lords of the Isles a lot later if you want to pander to 21st century Gaelic imperialism.