Jim Dickson from Argyll has asked me to spread the word on feedback he has had from Steve Hampton in the USA re the Argyll ‘Thayers’ Gull. Steve is a leading light on the ID of this taxa, so certainly worth taking a few moments to read this through:
It’s nice to have such great photos! This looks like a typical Thayer’s Gull. We have several hundred present here now and this bird would fit right in. I can’t imagine anyone on the West Coast, and probably not even the East Coast, of the US, would consider calling this a Kumlien’s. It would certainly not be accepted as one in California; it would be called “a fairly typical Thayer’s”.
I assume you’ve seen the birds at http://www.tertial.us/gulls/kuml1.htm (which I keep adding to).
Using my scale and going point by point:
PRIMARIES – 4; very typical; the size of the pale edge is variable and there is nothing remarkable here for Thayer’s
SECONDARIES – 4; seems to be a strongly contrasting dark bar (at most lighting angles); very typical of Thayer’s
TERTIALS – 3.5; the solid interiors are a tad paler than normal, but still concolor with the covert markings; this is seen on many Thayer’s and, in Calif, would not get me excited about a possible Kumlien’s
TAIL – 4; there no evidence of a pale shadow band or unusually large pale tips– what you see here is pretty typical. Actually, most Thayer’s have more pale baring at the base of the outer rectrices, producing a more banded rather than solid tail look.
COVERTS/BODY – 3.5; some Thayer’s can be positively frosty here, close to a 2; this bird is not a dark checkered as some, but the amount of white vs brown is nothing abnormal.
BILL COLOR – 3; only because the good photography is picking up the dusky red tones; in the field I’d probably call it a 4; again, nothing unusual;
HEAD/BILL SHAPE AND SIZE – 3; this feature varies a full point between males and females; this bird feels like a female Thayer’s, based on the refined bill and small gonydeal angle; note the elongated face toward the bill, typical of Thayer’s. Kumlien’s/Iceland have steeper foreheads and more dove-like heads.
So the total score is 25. I imagine West Coast birders would call this a Thayer’s quite comfortably.
Food for thought. A Bill Allan photo of the bird in question attached. Other pics are on this blog if you care to trawl back.