|Thayer’s Gull: from top left to right bottom: 1) Denmark Kent Olsen; 2) Canada Brandon Holden; 3) Denmark Kent Olsen; 4) Canada Brandon Holden; 5) Denmark Kent Olsen; 6) Denmark Kent Olsen.|
|Thayer’s Gull: from top left to right bottom: 1) Canada Brandon Holden; 2) Denmark Kent Olsen; 3) Denmark Kent Olsen.|
People have criticised the head and bill shape. However, where comparing with these gulls Ontario, Ontario, Ontario, Ontario, Minesota, Nevada, Japan, Califonia, Califonia, Califonia, Califonia, Califonia, Lake Michigan, Newfoundland, British Colombia, Oregon, Japan, Japan og Norway I see so many similarities with the Danish gull here, here and here. Please note hove the head shape changes with behaviour, i.e. the flat forehead seen when it was feeding among Great Black-backed Gulls vanished when it landed on the nearby roof.
For additional comparison look at figure 6 in this paper on plumage development in captive Thayer’s chicks caught on Victoria Island in Arctic Canada. What a massive bill and flat forehead.
Kirk Zufelt has written two blog posts on size variation in Thayer's Gull part 1 and part 2 based on experiences from eastern Lake Superior in Ontario. He says that: ‘Thayer's Gull is thought of by many as a relatively finely structured gull with a rounder head and finer bill than the Herring. Indeed the females are usually structured in this fashion. This however is not a diagnostic field mark at all. The male Thayer's can be quite robust and to my eye are near indistinguishable from the Herring Gull by structure. In fact many male Thayer's are much more robust and "Herring Gull-like" in structure than the female Herrings. In the field I look closely at all the round headed petite look birds with most of them ending up being Herrings. The bottom line is the structure is a good way to narrow down the field but it is far from diagnostic’.
The pale eye ring has also been discussed, but again that character is also seen in other Thayer’s Gulls such as these from Lake Michigan, Califonia, California, Minesota, Ontario, Ireland, British Colombia and Ontario
I would be very interested if anybody could break down the Danish bird in a detailed analysis.