ajohn

Mike's question is about the bird showing black below the eye, not the bill. I am not aware of this being a feature of Northern, it is not mentioned in the first paper, and the photos in the first paper appear to show black below the eye. Perhaps a misunderstanding?
The relevant feature is whether there is black below the bill, and I agree that the bird in question does not show black below the bill (the last photo does, of course, but that's a different bird!)

ajohn

The last photo in the lnik from Brendan shows dark-centred longest undertail coverts. Does this favour Asian over Northern? Of course, it may not be the same bird as in other photos.
Paul, I remember discussing this photo with you before. I think at the time you favoured dasypus for these. You were watching the martins at MP car park that day, and did not report any as being potential Northerns.