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first cycle
Glaucous-winged x Herring Gull

Fig 1) A psuedo-Thayer's Gull, but too large and too muddy and too far advanced in molt. This one, presumably a male, has the large bill of a Glaucous-winged Gull, but with some pink in it from the Herring side. December 10, 2011. Davis, California. Photo by Steve Hampton.

Fig 2) This bird resembles a large very thick-billed Thayer's Gull with an unsual covert pattern. It could be Glaucous-winged x Western, but the extensive white in the covert pattern is more likely from Herring. December 17, 2011. Davis, California. Photo by Steve Hampton.


Fig 3) These two are the same bird. It looks bulkier in this image and much closer to Glaucous-winged in structure. Note the solid tail; Thayer's would always show some barring on the outer rectrices at least. December 27, 2011. Redding, California. Photo by Ray Bruun.

Fig 4) Because it still has juvenile scapulars, it superficially resembles a Thayer's Gull. However, the lesser and median coverts are rather messy, not neatly checkered, and the greater coverts are extraordinarily plain, which is fine for Glaucous-winged but very wrong for Thayer's Gull. The bill is rather thick, and note the small-eyed look-- Thayer's typically imparts a big-eye-on-a-dainty-head look. December 27, 2011. Redding, California. Photo by Bob Yutsy.


Figs 5 and 6) With its juvenile plumage (rare for this hybrid this far into winter) and plain greater coverts, this bird suggests Slaty-backed Gull. The scapular pattern, however, is not correct for Slaty-backed, which should show contrasting subterminal anchors and more contrasting lesser and median coverts. January 14, 2013. Davis, California. Photo by Steve Hampton.

Fig 7) This bird seems like a regular Glaucous-winged Gull, except that it is so well-patterned on the coverts and tertials. The bill is typical for a Glaucous-winged Gull. It is still in juvenile plumage except for a few first winter feathers coming in on the scapulars. January 20, 2000. Palo Alto Baylands, California. Photo by Mike Rogers.

Fig 8) Glaucous-winged x Herring on the left; second cycle Thayer's on the right. Based on the gentle head and bill, these both appear to be females. January 29, 2013. Davis, California. Photo by Steve Hampton.

Fig 9) This bird has a strong, dark bill like Glaucous-winged, yet very straight-sided like Herring. The bill size and structure precludes Thayer's, which this bird otherwise resembles. February 2, 2012. Sausalito, California. Photo by Steve Hampton.

Fig 10) A true Slaty-backed mimic, but notice the pale blue-gray feathers coming in on the shoulder of the scapulars. February 6, 2012. Paradise Cove, Marin County, California. Photo by Steve Hampton.

Fig 11) This bird seems too streaky, too messy, too large-billed, and too advanced in scapular molt for a Thayer's. That's a first cycle Mew Gull in the background. February 12, 2012. Sausalito, California. Photos by Steve Hampton.


Fig 12) This bird is distinguished from Thayers' by the large black bill, small beedy eye, rather plain greater coverts, and molted back and scapulars. February 16, 2012. Petaluma, California. Photos by Steve Hampton.

Fig 13) A typical Thayer's in the background (and 2nd cycle Herring) provide a comparison. February 34, 2012. Petaluma, California. Photos by Steve Hampton.

Fig 14) Best described as a large blurry Thayer's Gull, note the rounded head, the bill shape and color, the folded primaries, and the messy patterning on the upperparts (including the greater coverts and tertial tips). February 24, 1998. Santa Clara County, California. Photos by Mike Rogers.


Figs 15 and 16) Same bird as Fig 14. Note the Thayer's like pattern on the flight feathers, with dark outer webs and pale inner webs all the way out to P10. Slaty-backed has more solid (and usually darker) P9-10 and more pronounced terminal spots on the inner primaries. In flight, the darkest colors on this bird, on the outer webs of the flight feathers and on the tail, are a fairly washed brown. Slaty-backed is usually a tad darker in these areas than this bird.

Fig 17) The bird in the foreground appears to be a typical late season hybrid. Some adult gray is coming in on the mantle, and the coverts are very faded. The brownish bird just behind is a Thayer's Gull, one of the most similar species to this hybrid. Note the Thayer's finer bill and smaller head. The standing bird is a California Gull, while the others are Herring Gulls. March 11, 2011. Davis, California. Photo by Steve Hampton.


Fig 18) Another late season bird, although they usually appear fairly muddy thru much of the winter. A Thayer's Gull is to the left. March 16, 2011. Davis, California. Photo by Steve Hampton.
Fig 19) Figures 19-21 are the same bird. It looks like a Glaucous-winged Gull with darker primaries. Thayer's is ruled out by the bulky size and advanced worn coverts. March 23, 2011. Clearlake, Calfornia. Photo by Steve Hampton.


Fig 20) In flight, the dark/like pattern, although muted, resembles Herring Gull. This pattern rules out Gl-W x Western Gull.
Fig 21)

See this page to compare with Slaty-backed Gull