It is a case of educated guesswork based on experience, gut feel along with a number of plumage characters that when pieced together get you to a second-winter Thayer's Gull. However, with just a week to play with, it was a steep learning curve so hopefully this load of shots will be useful. Certainly compiling and writing about them has been useful to me so please do enjoy and do comment.
|Photo 4. 2nd-winter Thayer's Gull, Jenner, California Feb 2013 a long-winged bird showing the neatly fringed brown primaries, 'fat feathering' that sometimes this species seems to show on its throat and solidly brown based tertials|
|Photo 9. 2nd-winter Thayer's Gull, Petaluma, California Feb 2013. Perhaps a fairly typical bird, with chocolate primaries fringed pale, obviously dark tertials and note the rather squat appearance caused by quite deep pink legs|
|Photo 12. 2nd-winter Thayer's Gulls, Milpitas, California Feb 2013. Two contrasting birds in terms of moult, as well as the bird in the foreground appearing more snouty. Both are typically long-winged with dark brown primaries|
|Photo 13. 2nd-winter Thayer's Gull, Golden Gate Park, California Feb 2013. Close inspection shows a pale eye on this bird. Otherwise fairly typical with a mantle shade coming through that is a tad darker than American Herring Gull|
Hi Rich, Having seen your shots I was wondering about the extent of pale fringing on the primaries.The Garner/Gibbins article says, i think,the pale fringe should be more or less confined to the tip of the primary but some of your birds show a more extensive fringe especially on some inner primaries. Just wondering if its a more variable feature than previously suggested. Paul Moore, CorkReplyDelete
Hi Paul thanks for the comment. I think that 2nd-winter Thayer's Gulls is yet (and perhaps never will be?) a precise science and I think that Garner/Gibbins focus on birds in December whereas a couple of months on the birds seem to show overall a lot more wear and I guess this is reflected in the primary fringing being more extensive on my visit. As an example, look at the recent Thayer's Gull in Spain (now an adult of course) when it was around in March 2010 http://www.rarebirdspain.net/arbsr1003.htm#Lartha (scroll down)ReplyDelete