Came across a small group of Eiders yesterday in West Voe of Sumburgh, although the flock contained just 5 birds (2 females, 3 males), two birds proved to be very interesting indeed.
Bird One - I'm pretty happy was a Borealis, based on current criteria - strongly yellowish bill and rounded lobes, plus the remnants of sails (mostly worn away over the winter). It must be stressed that anyone looking around the internet for definite identification criteria on this subspecies - it's an absolute minefield, the conclusion that I've come to is that borealis probably doesn't exist, and that borealis/mollissima are all just one North Atlantic cline !
Bird Two - This bird had massive rounded lobes that suggest Dresseri, however, the bill colour was again strongly yellowish and the black area bordering the bill was a long, thin triangle (as with borealis/mollissima), this bird did not appear to have any sails. Conclusion - this bird could possibly be a Dresseri x borealis/mollissima hybrid.
Any thoughts on this subject are most welcome.
Bird One Photos -
Bird Two Photos
And finally, the two birds together