I've re-read the BB paper (Stoddart, Dec 2013), thanks for reminding me about that one Barrie. I've also re-read Lee Evans paper http://www.gloucestershirewildlifetrust.co.uk/sites/default/files/The-Separation-Of-Lesser-%26-Mealy-Redpolls.pdf . As Stoddard suggests redpoll taxonomy and identification is in a bit of a state of flux.
This pair were on the feeder - 10/05/2015
Here's one from Papa Westray - 25/04/2015
The whitest, arcticist Mealy I've ever seen!!
Here's the first one from 26th April.
I think this is cabaret. Small size, really rather tiny when compared with the Greenfinch. Strong, dense flank streaking to the flanks behind the legs.
Same bird again.
Generally brown plumage tones, buff greater covert bar, relatively dumpy looking shape, short tailed. This bird did not readily show its rump, so that feature was not well seen, but in this picture the upper tail coverts look rusty brown, there's no hint of white and it would be surprising if this colouration did not extend to the rump. As MG stated on Orkbird, there is nothing here to suggest other than cabaret.
Same bird again.
Bill shape and the broad very dark feather in the undertail coverts also point towards cabaret.
Later the same day a redpoll was heard and seen very briefly in a Harray garden, about 1km distant. This looked quite large and grey but was seen rather briefly. Call seemed quite low pitched.
The next birds turned up on 30th April. Two were feeding in the conifers next door, these were presumed to leave to the south with two others. One of the two birds, seen well, if briefly, was a very pink male. When the left, calling the trill was I thought higher pitched than the Harray bird of 26th. Later a single bird appeared on the feeders.
Bird 2, 30th April
This individual looks immediately larger next to the Greenfinch, and has a very pale, grey background colour to all the plumage. The greater covert bar is tipped white, the tramlines on the back are white. However, the streaking is strong on the flanks and extends nearly to the undertail coverts, could this be a Greenland/Dark Iceland Redpoll? I think this is f.islandica.
Interestingly this bird did not associate with the flock of four, and when initially one of those returned, or a different bird perhaps, they were not seen at the feeder concurrently (for the first day anyway). Bird 2 often showed its rump which had a white ground colour.
The rump looks very white
This is Lesser Redpoll (cabaret), from 3rd May. It was present with the dark Greenland/Iceland flammea islandica and when the two birds briefly faced side by side looked to be about 85% of the size.
Bird 4 from 21st May, present until 23rd May
Rather cabaret like, apparently brown plumage, quite large dark feather in undertail coverts. However, broad white greater covert bar, and broad white median covert bar,
Looks small in this picture, supporting cabaret, but very white background colour to mantle.
Clearly has a white rump with, apparently, little streaking. From this view looks much more like flammea.
My view would be that this is flammea but I'd be interested in any argument to support or contradict this view.