Iceland Gull (glaucoides) 1st cycle, February 14 2009, Peterhead, Scotland (Chris Gibbins). Classic glauoides. White outer primaries; arrow points probably faded away by February. Such white winged individuals pose no problems.

Kumlien's Gull (kumlieni) 1st cycle, January 20 2013, Michigan City, IN. (Amar Ayyash). Dark outer-webs on primaries, secondary bar darker than wing-coverts and dark solid tail bar.

Iceland Gull (glaucoides)? 1st cycle, February 02 2008, British westcoast (Chris Gibbins). Darker end of the spectrum, dark on underparts. Arrow points at primaries and juvenile plumage.Outer-webs of visible primaries lack dark patches.

Kumlien's Gull kumlieni 1st cycle, St. John's, Newfoundland (Dave Brown). Dark centres on rectrices, dark outer primaries and extensive dark centres on tertials. Birds like this should be eye-catching: glaucoides in jizz, with dark elements.

Iceland Gull (glaucoides) 1st cycle, February 26 2012, Peterhead, Scotland (Chris Gibbins). Rather dark-winged Iceland Gull, with the outer-webs of the primaries all darker than inner ones. Still, there is a uniform pattern, as this pattern is repeated across all primaries, with inner primaries darker, if anything, than outers. In typical glaucoides, the very tip of the outer-webs are white, with obvious chevrons or ´arrow-head patterns´ on the central and inner primaries. Also, there is extensive spotting just above the chevrons, continuing to halfway the feathers in P1-P3, and less extensive central primaries, but even still obvious on P6. This pattern is copied on the tips of the greater primary coverts, and worth checking, as patterns on exposed primary tips can easily bleach and wear away (making exact valuation of original patterns difficult), while the primary coverts are often hidden in resting birds so patterns are better conserved.

Kumlien's Gull (kumlieni) 1st cycle, January 23 2013, St. John's, Newfoundland (Jan Baert). Pale bird, close to some 1st cycle glaucoides, but:
- wing-tip pattern is a plain brown wash over the centre of the outer primaries and extending almost to the feather tips. The outer 5 primaries show dark outerwebs and pale innerwebs and a dark ‘hook-back’ at the wing-tips. These dark outer primaries contrast with less well marked, paler inner primaries. In this pattern it recalls 1st cycle (juvenile primaries in) thayeri.
- tail-bar contrasts with paler, dark-barred uppertail-coverts. A dark tail-bar is present in 15% glaucoides, in 80-95% kumlieni. The tail-bar of kumlieni is often rather uniform, just with faint pale (often broken) mottling at tip of tail and along edges of T1-T2, whereas tail-bar of glaucoides typically consists of narrow bars melting together. Thayer’s usually has darker, mud-brown tail-bar with pale mottling restricted to base and edges of rectrices.

Iceland Gull (glaucoides) 1st cycle, December 20 2011, Neeltje Jans, the Netherlands (Edward Minnaar). Slight contrast in shade of grey-brown on primaries, with outer-webs of outer primaries darker than the inners (which advocates kumlieni). Sub-terminal chevrons most obvious on inner primaries. Pattern of tail-band broken by much vermiculation, where typical kumlieni shows a more solid band, especially on the centres of the feathers. Also secondary centres do not form a darker band.

Kumlien's Gull (kumlieni) 1st cycle (2CY), February 14 2015, Madison, CT (Keith Mueller). Outerwebs on outer primaries are darkest part of the primaries, the secondary bar is darker than the brown tone on the wing-coverts and this bird has a dark solid tail bar. This combination should place the bird outside the limits for glaucoides.

Iceland Gull (glaucoides) 1cy, December 04 2010, Fraserburgh, Scotland (Chris Gibbins). Pale individual, with whitish outerwebs of outer primaries, whitish centres of secondaries, but surprisingly solid dark centres of rectrices.

Kumlien's Gull kumlieni 1st cycle, December 30 2010 (Ryan J Sanderson). Warm reddish brown patterns, as in many glaucoides. Typically kumlieni has the outerwebs of the outer primaries darker than other parts of the primaries. Also, the outerwebs of the secondaries are dark, creating a dark secondary band in flight (here this effect is gone, the band in interrupted, now the bird is landing). Finally, kumlieni often has solid dark centres on rectrices.

Herring Gull (argentatus) 1st cycle RUM ES14266 October 22 2012, Scheveningen, the Netherlands (Mars Muusse). Ringed in Murmansk, N Russia. In Herring Gull the juvenile scapulars are two-toned, not three-coloured: brown centre and pale notches.

Thayer's Gull 1st cycle, December 10 2011, Everett, WA. (Steve Mlodinow). Still completely juvenile. Three-coloured juvenile scapulars: pale brown centre, dark sub-terminal line, pale fringe.

American Herring Gull smithsonianus 1st cycle, December 11 2013, Tompkins Co, NY. (Kevin McGowan). Like Thayer's Gull, largely juvenile plumage (probably from northern population). These northern birds often powerful, heavy built and pear-shaped head ('snouty').

American Herring Gull smithsonianus 1st cycle, November 19 2011, Berrien County (Amar Ayyash). Uppertail coverts and tail pattern similar to Thayer's Gull, but pale window restricted to inner primaries.

Thayer's Gull 1st cycle, February 05 2011, Westmoreland Park, OR. (John Rakestraw). Bird in juvenile plumage by February. Black bill with paler base. Note extensive dark tertial centres and pale crescents on primary tips.

Herring Gull 1st cycle, February 07 2013, Katwijk, the Netherlands (Mars Muusse). Different from Thayer's in following respects: much proximal white in rectrices, pale-looking uppertail coverts, window restricted to inner primaries, no pale innerwebs on outer primaries.

Herring Gull 1st cycle, February 14 2012, Noordwijk, the Netherlands (Mars Muusse). Sometimes Herring Gull show paler innerwebs on outer primaries, but then birds are very pale overall, especially on rump and in the tail.

Thayer's Gull 1st cycle, February 03 2013, Boulder County, CO. (Amar Ayyash). Pale window continues to the inner webs of the outer primaries (base of innerweb of P10 pale). No dark pigmentation on the innerweb tips of P1-P4. Tail largely blackish. Uppertail coverts densely barred.

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IMMATURE THAYER'S GULL VS EUROPEAN HERRING GULLS

An extensive PDF has been published by Chris Gibbins, dealing with 2nd cycle Thayer's Gull. His key points for 2nd cycle Thayer's are:
- shape and size in-between Iceland Gull and Herring Gull,
- smudgy underparts and much brown in the wing,
- tertials with solidly brown centres, only vermiculated along tip,
- greater coverts often uniform mid-brown,
- short legged,
- almost completely dark brown tail,
- heavy, dense barring on uppertail and undertail coverts,
- round-headed and finer billed than Herring Gull,
- late moult.

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Herring Gull (argentatus) 2nd cycle JN336 January 09 2012, Neeltje Jans, the Netherlands (Pim Wolf). From N Norway (70°23'N). No grey scapulars Note broad barring on tertial tips and barring on inner greater coverts.

Thayer's Gull 2nd cycle, February 24 2009, Vancouver Island, BC (Guy Monty). Delicately built. 2nd generation primaries, pink base of bill and single grey-based feathers in scapular region. Note pattern on tertials and greater coverts.

Herring Gull (argentatus) 2nd cycle KV48 January 15 2008, Boulogne-sut-Mer, France (Jen-Michel Sauvage). From Murmansk, Russia (67°05'N). Northern argentatus often have 'snouty' head: long bill and sloped forehead. Bulky structure and stronger head-bill proportions than Thayer's. Only tiny white tips on 2nd gen outer primaries.

Thayer's Gull 2nd cycle, December 08 2012, Lake County, IL (Amar Ayyash). 2nd gen flight feathers, P10 with 'ghost mirror'. Fine vermiculation on the tips of P1-P4. Scapular region almost completely grey, but still intermixed with faint grown feathers. Tail almost completely dark and bill predominantly dark.

Herring Gull 2nd cycle, January 23 2013, Katwijk, the Netherlands (Mars Muusse). Outer primaries with dark innerwebs. Some birds have a weak mirror on 2nd generation P10. Much proximal white in tail and markings on uppertail coverts is widely spaced.

Thayer's Gull thayeri 2nd cycle (3CY), December 28 2012, Half Moon Bay, CA. (Chris Gibbins). Notice the dark secondaries of this Thayer's, matching the primaries and tail in tone. In Kumlien's all three of these feather groups are normally significantly paler brown than in Thayer's.

Herring Gull 2nd cycle, October 09 2012, Katwijk, the Netherlands (Mars Muusse). Overall dark bird, outer & central primaries with dark innerwebs. Much black in tail and strong contrast with pale uppertail coverts.

Kumlien's Gull (kumlieni) 2nd cycle, February 16 2012, St John's, Newfoundland (Dave Brown). Many grey scapulars. Primaries pale brown with broad pale fringes, tertials and greater coverts with much vermiculation and spotting. Note overall 'milky' tone.

Thayer's Gull thayeri 2nd cycle (3CY), February 12 2012, Sausalito, CA. (Steve Hampton). Typical second cycle bird. Tertials extensively solid dark brown lacking vermiculation at fringes. Note the rather solid brown, slightly marbled greater coverts.

Kumlien's Gull (kumlieni) 2nd cycle, January 22 2012, St John's, Newfoundland (Bruce Mactavish). Few adult-like grey scapulars; bird very 'milky' overall. Primaries pale brown with broad pale fringes, tertials and greater coverts with much spotting.

Thayer's Gull thayeri 2nd cycle (3CY), February 18 2012, Davis, CA. (Steve Hampton). Advanced bird with almost completely grey saddle. Dark centres of tertials. Outer primaries darkest part in resting bird (dark brown, not blackish), lacking Kumlien's broad white fringes.

no / very few spots

Iceland Gull (glaucoides) adult, January 13-14 2012, Peterhead, Scotland (Chris Gibbins). Classic bird, but with speckled iris. Unmarked white wingtip. Pearl-grey upperparts.

Iceland Gull (glaucoides) adult, January 21 2012, Peterhead, Scotland (Chris Gibbins). Glaucoides population homogeneous: pearl grey upperparts; no sub-terminal bands; at most only very faint parallel grey lines on P9-P10 along feather edges; no speckling in iris.

Kumlien's Gull (kumlieni) adult, February 07 2012, St John's, Newfoundland (Dave Brown). Bird too dark for glaucoides and yellowish iris is extensively mottled brown. Wingtip in palest end of spectrum for kumlieni.

Kumlien's Gull (kumlieni) adult, February 10 2007, St John's, Newfoundland (Chris Gibbins). Wingtip in palest end of spectrum for kumlieni, lacking sub-terminal bands. However, parallel dark lines along edges of P7-P10. Pigmentation is pale grey.

Kumlien's Gull (kumlieni) adult,, February 07 2012, St John's, Newfoundland (Dave Brown). Still wingtip in palest end of spectrum for kumlieni, lacking sub-terminal bands. However, parallel dark lines along edges of P7-P10. Pigmentation is dark grey. Upperpart grey tone darker than glaucoides.

Kumlien's Gull (kumlieni) adult, January 23 2013, St. John's, Newfoundland (Jan Baert). Sub-terminal bands and lines along edges of P7-P10. Pigmentation is pale grey. Bird with pale iris.

Thayer's Gull adult, January 20 2008, Vancouver Island, BC. (Guy Monty). Birds in winter (non breeding) plumage. Each spring a significant percentage of the world population of this species masses in this area to fatten up on Pacific Herring and their roe during the annual spawn.

Herring Gull adult, January 23 2013, Katwijk, the Netherlands (Mars Muusse). With thayeri pattern on P9-P10.

Thayer's Gull adult, March 07 2011, Vancouver Island, BC (Guy Monty). Upper bird: P10 with broken sub-terminal band and single spot on P5. Lower bird: No sub-terminal black on P10, single spot on P5. Both bird with broken medial bands, so-called "thayeri pattern".

Herring Gull argentatus adult, December 06 2013, Noordwijk, the Netherlands (Mars Muusse). Grey tone as in argentatus from N Scandinavia. P9 and P10 no sub-terminal band and no medial band; hardly any black on innerweb. P6 black on outer-web only. Just within limits of argentatus, or argentatus x hyperboreus.

Thayer's Gull thayeri adult, February 11 2012, Pelagic - Lewes, DE (BirdFellow). Dark iris and mottling on head running down on breast. Obvious thayeri pattern on P9 (broken medial band).