Adult males. The markings on the bill are rather alike and characteristic for the males of the species. Notice the different head shape, where the one behind shows the classic profile with the top point at the rear of the head. The eye color is bright yellow orange on old males, but variation occurs as it is obvious here. The brownish feathers on the flank of the front bird, are reminiscents of the eclipse/alternate plumage of the adult male as I see it, rather than being an indication of a young bird.
Adult male. Here showing the classical bill markings and head profile. Notice that the white spur on the flank is almost absent. Also notice the chestnut colored ring patch low on the neck. Apparently the species has been named after this. As the winter progresses it becomes even more prominent.
Adult male. Other than 1431. Appears more advanced in molt with cleaner flanks. On the other hand this one shows no sign of neck collar, but could be hidden behind other neck feathers.
1cy male and probably 1cy female. The male to the left shows darker feathers on the head and the back than corresponding females. The female looks like the same as 1426, based on the white markings on the bill.
Adult male. Unmistakable in breeding plumage, and easily separated from the sister species, Tufted Duck, as seen in these photos. Rare visitor in Denmark, even though this bird has returned to Søndersø during the last 5 or 6 winters. Despite of this, the bird became a new DK species for me. A slow twitch indeed.