Possible Thayer's Gull Cape Ann, MA - December 30th.

January 2nd - After several observers reported seeing the same bird over the last few days, Phil Brown captured an excellent new image set from Niles Pond: http://www.nebirdsplus.org/PossTHGU.htm
In Phil's flight shots, note especially the isolated small pale mirror on the outermost primary on the right wing. Could this be another pointer towards an identification of Thayer's? It's illustrated and mentioned for third cycle birds in Malling Olsen & Larsson, and the new Howell and Dunn (Gulls of the Americas) includes it for second cycle birds as follows;
"P10 rarely has small diffuse mirror". [Update: January 3rd] Further reading of Howell and Dunn (Gulls of the Americas) describes second cycle Kumlien's Iceland Gull as "sometimes (showing) a faint P10 mirror" and even second cycle American Herring Gull - "very rarely, a small, diffuse, P10 mirror". The latter, especially came as a bit of a surprise but clearly we can't place too much emphasis on the presence of a small mirror on P10 for this bird.

Here's some excellent photographic references to Thayer's Gulls, including second cycle birds;

From California by Jeff Poklen
From British Columbia by Michael G. Sheperd.

(possible second cycle Thayer's Gull - lower left)

Found late in the afternoon after a fairly intense day of gull watching around Gloucester and Eastern Point, this second-cycle gull showed a number of characters that prompted me to start thinking about Thayer's Gull. Watched at range with Scott Surner on Niles Pond in fading light. Conditions were far from ideal for digiscoping. However, this image set should at least illustrate the bird that we observed and some of the reasoning behind the suggested identification of Thayer's.

(possible 2nd cycle Thayer's lower right with American Herring Gulls).

(possible 2nd cycle Thayer's in foreground with American Herring Gulls).
Contrastingly dark primaries showing pale whitish tips.

(possible 2nd cycle Thayer's lower right with American Herring Gulls).
Slightly smaller in size compared to American Herring Gull but with more
rounded head shape and shorter bill. This bird showed a strikingly bicolored bill.
Dark primaries not always obvious, with the bird at rest appearing Kumlien's like at times.

(possible 2nd cycle Thayer's in foreground with American Herring Gulls).
Showing contrastingly dark primaries. Note thin pale fringes to primaries
with prominent pale tips. Tertial centers are much lighter than primaries.

(possible 2nd cycle Thayer's in foreground-left with American Herring Gulls
and 1st cycle Kumlien's Iceland Gull, right).

(possible 2nd cycle Thayer's in bathing in center with American Herring Gulls
and Great Black-backed Gull).

(possible 2nd cycle Thayer's in flight. Showing solid brown subterminal tail-bar,
dark outer primaries but translucent on rest of primaries). Detail of same image below.

Note narrow dark tips to outer primaries which extended to more
of the primaries than shown in this shot but observed well in the field.

Distinctly dark brown outer primaries on upperwing.

(possible 2nd cycle Thayer's in flight. Showing solid brown subterminal tail-bar,
dark brown outer primaries but with rest of primaries pale).
Passing over young Kumlien's Iceland Gull.

This bird was also seen and reported at Niles Pond on December 31st, 2007. Hopefully further observations will facilitate more thorough documentation.


GB,

JPS.