On my monitor the left tern shows a greyish uppertail with white sides.
If I understand you right Sean - by saying that 'all the primaries' should be black on a Saunderīs Tern - you really mean that Saunderīs has a 'wider' black area on outer
primaries compared to Little Tern.
As staded in an earlier post I find it difficult to be sure of the identification of these two in this image (no disrespect Adrian
). I for once canīt see the head pattern properly, because thatīs what I want to see before I draw any conclusions. We also have to consider that Little Terns in the area might show grey central tail (but paler rump) and intergrades occcur.
Any more Adrian?