A few updates for those with enough patience to persevere with this thread.
Mongolian Gulls first. The cracking 'typical' fresh first-winter (first photo) was around on and off this weekend, permitting more photos. It has been joined by a second, more cryptic individual (actually the fifth bird in #138 above) (remaining photos). This bird lacks much of a window in the inner primaries, but does have a row of pale spots there.
It is Mongolian rather than Taimyr due to completely replaced (white, rather than blue-grey) scapulars, no evidence of feather replacement in the wing, notches/patterns in the outer greater coverts, and a brownish look to the hand (it is pretty obvious where this bird is going the bleach).
Mongolian Gulls first. The cracking 'typical' fresh first-winter (first photo) was around on and off this weekend, permitting more photos. It has been joined by a second, more cryptic individual (actually the fifth bird in #138 above) (remaining photos). This bird lacks much of a window in the inner primaries, but does have a row of pale spots there.
It is Mongolian rather than Taimyr due to completely replaced (white, rather than blue-grey) scapulars, no evidence of feather replacement in the wing, notches/patterns in the outer greater coverts, and a brownish look to the hand (it is pretty obvious where this bird is going the bleach).