Sunday, February 12, 2012

What's your Thayer's-type?

What a headache.  After spending a total of around ten hours this week looking at gulls at Fort Baker near Sausalito, CA this week, I have just about nothing to show for it.  We missed the Iceland Gull seen well early this week by many, and missed Slaty-backed Gull, of which there were as many as three!  Sure we had two different Glaucous Gulls on two different days (one first cycle, one second cycle), but I can't help but feel bitter, like I wasted my time.  Then again, I saw more Thayer's Gull's this week than I ever had in my entire life (roughly x100).  Though these were mostly first cycle birds, there were a lot of adults and in-betweeners as well.
Typical (?) First-cycle Thayer's Gull. Note: Short, relatively thin, straight, solid black bill, gently curved culmen, dome-shaped, dove-like head, though slightly sloped forehead, dark pink legs, dark iris, primaries darker than body and tertials with pale crescents at tips, tertial centers darker than coverts, checkered/barred wing coverts, scapulars mostly pale with dark centers giving a checkered appearance, tail with broad terminal dark band. [Photo by Lukas Musher]
Adult Thayer's Gull. Note: Bill and head structure as above, pale gray mantle, mostly gray primaries.  Very large subterminal mirror (white spot) on P10 (outermost primary) and relatively large mirror on P9 (second most distal primary), black restricted to outer web of primaries.  Streaked head (winter). [Photo by Lukas Musher]
Adult Thayer's Gull.  Head and bill structure as above.  Fairly dark iris, bright pink legs, apical spots (terminal white marks on primaries) relatively even generally becoming larger as you move anteriorly (tail to head) along the folded wing. [Photo by Lukas Musher]
Adult Thayer's Gull.  [Photo by Lukas Musher]
Adult Thayer's Gull.  [Photo by Lukas Musher]
Adult Thayer's Gull.  [Photo by Lukas Musher]
A somewhat dark first cycle Thayer's.  Pale crescents at tips of primaries beginning to wear off.  [Photo by Lukas Musher]
First cycle Thayer's Gull.  Note: Dark secondaries with pale tips, dark outer primaries, pale inner primaries.  Rather checkered-looking median coverts. [Photo by Lukas Musher]
Adult Thayer's Gull.  Note: Bill/head structure as above, small gonydeal bulge (variable, but generally smaller than  herring and other larger-billed gulls), deep pinkish-purple orbital ring, dark yellow-honey iris. [Photo by Lukas Musher]
First cycle Thayer's Gull.  [Photo by Lukas Musher]
First cycle "Kumlin's" Iceland Gull for comparison.  Kumlien's Gull has been treated variously as a hybrid Iceland x Thayer's, and a subspecies of Thayer's or Iceland.  Currently it is categorized as a subspecies of Iceland Gull: Larus glaucoides kumlieni.  [Photo by Lukas Musher]
Kumlien's Gull again. [Photo by Lukas Musher]

By Luke Musher

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