(gavia immer)
The 'authorities' would have us call these Great Northern Loons but nobody ever uses that name.
The Great Northern Diver is a winter visitor to Scotland, the breeding areas being far to the north around ponds and lakes in both the coniferous areas and in the treeless areas of Iceland, southern Greenland and Bear Island. The Scottish winter population numbers from 1000 to 3000 birds being mostly found in coastal waters off the Northern and Western Isles. A smaller number of birds may be found in western sea lochs in the early summer, these likely being sub adult non breeding birds. From a trip on the Kennacraig-Islay ferry we saw several summer plumage Great Northern Divers in West Loch Tarbet and on Islay there were a few birds in Loch Indaal.
Note the huge contrast between the drab grey winter plumage and the striking summer plumage.