glaucoides & kumlieni

(last update: October 12, 2011)

Coordinators:
Dave Brown (Canada)
Bruce Mactavish (Canada)
Chris Gibbins (Scotland)
Peter Adriaens (Belgium)
Mars Muusse (Netherlands)

Iceland & Kumlien's Gull adult September - December

Below you will find a description of The Iceland Gull Complex and Kumlien's Gull, as published in one of the best Gull piblication: "Gulls of the Americas" by Steve Howell & Jon Dunn.

"we" in the text below refers to the original authors. If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom.

THE ICELAND GULL (Larus glaucoides) COMPLEX

The Iceland Gull complex comprises two or three taxa of large white-headed gulls that breed in Arctic Canada and Greenland: glaucoides (Iceland Gull, breeding in Greenland), kumlieni (Kumlien’s Gull, breeding in ne. Canada), and perhaps thayeri (Thayer’s Gull, breeding in n. Canada). Kumlien’s Gull is generally treated as a subspecies of Iceland Gull (and almost all records of so-called Iceland Gulls in N. America are of this taxon), but the taxonomic status of Thayer’s Gull has been subject to much debate [Howell, 1998; Pittaway, 1999].

Recent field studies [Howell & Elliott, 2001; Howell and Mactavish, 2003] support the distinctness of Thayer’s Gull, which is treated as a full species by AOU [AOU, 1998], and Browning [Browning, 2002] recommended that Thayer’s, Kumlien’s, and Iceland be recognized as separate species until proven otherwise. Snell [Snell, 2002] argued for the lumping of Iceland (including Kumlien’s) and Thayer’s, although his data (for example, his table l) support the recognition of three distinct populations that correspond to Iceland, Kumlien’s, and Thayer’s. Most gull taxa are defined by morphological characters such as wingtip pattern, yet Snell’s [Snell, 2002] criteria for defining these taxa are somewhat circular: for example, nominate Iceland Gulls can have gray in the wingtips simply because such birds breed in Greenland; why are these not simply extralimital Kumlien's Gulls, as with Glaucous-winged Gulls that breed in cen. California? Compounding the problem, studies on the breeding grounds where Kumlien’s and Thayer’s presumably interbreed have either: 1) been spurious [Smith, 1966; Snell, 1989; Snell, 1991]; or 2) failed to define variation in the characters of these taxa [Gaston & Decker, 1985; Snell, 1989], so the degree of reported interbreeding is impossible to assess. Hence, we can’t learn how much Kumlien’s and Thayer’s interbreed until we can distinguish them, but we can’t distinguish them because they appear to interbreed. Given this uncertainty, we treat the three taxa in separate accounts, with Thayer’s Gull as a full species, but we recognize that much remains to be learned about this complex.

KUMLIEN’S GULL Larus (glaucoides) kumlieni

LENGTH 19-24.5 IN. (48-62 CM)

IDENTIFICATION SUMMARY

A medium-large to medium-sized, pink-legged gull breeding in the Canadian Low Arctic and wintering mainly in the nw. Atlantic. Bill relatively short and slender, parallel edged with a shallow to moderate gonydeal expansion. At rest, tail tip falls between tips of P6 and P7. Adult has pale gray upperparts (Kodak 4-5) with variable wingtip pattern (see images). Most birds have dark gray stripes and subterminal bands on the outer 4-5 primaries; a few birds are almost white winged (approaching Iceland Gull), and a few have darker wingtip markings (approaching Thayer’s Gull). ]uvenile medium brown to creamy overall with medium-brown to whitish wingtips. PA1 (1st pre-alternate moult) variable, starting Oct.-Apr. Subsequent ages variable in appearance. All ages have pink legs, often quite bright; adult eyes pale lemon to brownish, orbital ring purplish pink.

Adults mostly distinctive. Glaucous-winged Gull similar in plumage but much larger with longer and stouter bill, broad wings, short wing projection, slightly darker upperparts. White-winged adults most likely to be confused with Iceland Gull, which averages paler gray above with all-white wingtips, pale lemon eyes; Glaucous Gull notably larger and more massive with larger and thicker bill, relatively shorter wing projection, slightly paler gray upperparts, orange orbital ring. Dark-winged extremes similar to Thayer’s Gull: note that Kumlien’s averages paler gray above with slaty gray versus slaty blackish wingtips. See Similar Species section for more detailed identification criteria and separation from various hybrid combinations, all of which are larger and bigger billed than Kumlien’s Gull.

First-cycle Kumlien’s typically has brownish wash on outer primaries versus evenly pale primaries on Iceland. First-cycle Thayer’s larger and darker with longer bill, blackish brown outer webs to outer primaries, contrasting dark secondary bar. Glaucous Gull larger with a stouter bill that is sharply bicolored (pink with a black tip), short wing projection, generally whiter primaries.

TAXONOMY

Kumlien’s Gull was first described as a species [AOU, 1957], later viewed as a hybrid between Thayer’s Gull (then considered a race of Herring Gull) and Iceland Gull [AOU, 1931; Dwight, 1925] as a full species [Taverner, 1937], and as a subspecies of Iceland Gull [AOU, 1957; Godfrey, 1986]. It might yet prove to be a full species [AOU, 1998; Browning, 2002; Howell and Mactavish, 2003]. Field characters of adults based on wintering populations were proposed recently [Howell and Mactavish, 2003], but critical studies on the breeding grounds are still needed. See introduction to the Iceland Gull complex.

STATUS AND DISTRIBUTION

Breeds ne. Canada, winters N. Atlantic (including Iceland), rarely to nw. Europe.

Breeding. Breeds (]une-Aug.) in n. Canada on s. Baffin I. (north on e. coast to Home Bay and Broughton I.), e. Southampton I. (Bell Peninsula), and Coats I.; also Ungava Peninsula, nw. Que.

Nonbreeding. Southbound fall movements to Atlantic Canada can begin early Oct., but arrival there and coastal New England more regular after mid-Oct., with many more arriving Nov. On Great Lakes some arrive Nov. but most not until mid-Dec. or later. Arrivals on Mid-Atlantic Coast mainly Nov.-Dec.

Winters (Oct./Nov.-Mar./Apr.) mainly in Atlantic Canada (north to s. Lab.), with smaller numbers east to Greenland and south along Atlantic Coast of N. America to N.]., and in e. Great Lakes region. Rare (mainly Dec.-Mar.) south to Outer Banks, N.C., and on w. Great Lakes (very rare to casual on Lake Superior). Casual (mainly Dec.-Mar. in most areas, but mainly Nov.-early Dec. in Prairie Provinces) along Atlantic Coast south to Fla., on Gulf of Mex. coast west to s. Tex., in Mid-west well away from Great Lakes, in interior Southeast, on Great Plains south to Colo., and in the Northwest.

Northbound movements begin by late Feb., with most departing s. parts of winter range during Mar., and n. parts during Apr.-May; a few birds remain into June, very occasionally through mid-Aug.-Sept. in New England and Atlantic Canada, making it difficult to determine fall arrival dates. Regular on sw. Hudson Bay in summer (mid—May-Oct., mostly late May-early June), and casual (Sept.-Oct.) along Arctic coast of Alaska and in s. Yukon.
“Iceland Gull" in Bermuda termed “frequent but rare" (Amos 1991) with about 7 recent fall records (late Nov.-late Dec.) and 10 spring records (late Feb.-early Apr.), but subspecies usually unspecified (at least 2 records of kumlieni).

HABITAT AND BEHAVIOR

Breeds on cliffs and rocky islands in Canadian Arctic; adults winter mainly at sea and along the coast at fishing harbors, sewage outfalls, inlets, and beaches. First-winter birds (and, to an extent, other ages) also occur often at lakes, duck ponds, dumps, parking lots, and other habitats where large gulls occur. Nonbreeding birds (especially adults) often in flocks (locally up to a few thousand birds, but more often l00-1,000 birds). Kumlien’s Gulls associate readily with other gulls and water birds but, at least in winter, they often avoid feeding areas dominated by the larger American Herring and Glaucous Gulls. Feeds while swimming and in flight by picking and surface-plunging, and overall more aerial than Glaucous Gull. In winter, feeds on marine invertebrates and fish in inshore and offshore waters, often along and around leads in sea ice [Snell, 2002]; also scavenges.

DESCRIPTION AND MOLT

Note: some Kumlien’s-type birds have atypically dark wingtips (blackish gray on adult and third cycle, dark brown in first cycle and second cycle) and overall increased dark pigmentation in the flight feathers. Some of these are probably hybrids with Thayer’s Gull, but some may represent variation in pure Kumlien’s, the limits of which have yet to be satisfactorily established.

Adult Cycle. Complete prebasic molt (]une/]uly-Nov./Dec.) produces adult basic plumage: head, neck, and underparts white; head, neck, and sometimes upper chest with variable (usually moderate to heavy) dusky mottling and streaking. Upperparts pale gray (Kodak 4-5) with variable slaty gray wingtip markings (mostly Kodak 7-10). Most birds (about 70 percent) have slaty gray markings on P6-P10 or P7-P10 with complete dark subterminal bands on up to 3 primaries among P6-P9 and the most extensive dark markings on P8; P10 lacks a subterminal band and often has no subterminal gray markings; P9 has a white mirror typically extending across the outer web, and dark medial markings rarely extend onto the inner web. The least-marked wing-tips (9 percent of birds) have gray stripes along the basal to medial portions of the outer web and shaft of 1-4 primaries among P7-P10, and some birds (about 4 percent) appear completely “white winged” in the field. The most extensively marked wingtips (5 percent of birds) have dark marks on the outer 6 primaries but rarely a distinct or complete subterminal band on P5. White trailing edge to secondaries (often hidden at rest) and inner primaries. Uppertail coverts and tail white. Underwings show a ghosting of variable upperwing pattern. Eyes pale lemon to brownish, orbital ring purplish pink to reddish. Bill yellowish (often greenish basally in winter) with orange-red to red gonydeal spot and rarely a dark mark at gonys. Legs bright flesh pink, perhaps duller during height of prebasic molt.
Partial pre-alternate molt (Oct.-Mar./Apr.) produces adult alternate: head and neck clean  white (rarely before Mar./Apr.); white primary tips can be lost through wear. By spring, orbital ring brightens, bill brightens to lemon yellow with red gonydeal spot, lacks dark distal
marks.

First Cycle. Juvenile (Aug.-Apr.): medium brown to creamy overall. Head, neck, and underparts variably streaked and mottled whitish and brownish, becoming whitish on vent and undertail coverts which have fairly broad brownish bars. Upperparts marked with typically fairly fine brownish barring, checkering, and lacy patterning that varies from distinct and sharply patterned to muted and washed out (mainly from midwinter onward, when bleached). Uppertail coverts whitish with brownish barring. Tertials pale brown to whitish with variable, typically fine patterning similar to upperparts. Wingtips vary from medium brown with narrow whitish edgings to whitish overall with fine brown subterminal chevrons or spots; typically similar in tone to upperparts. Spread primaries often show a slightly paler panel on inners; secondaries medium-pale brown to whitish, not contrasting on spread wing. Outer primary coverts plain pale brownish to whitish, often with slightly darker subterminal marks. Tail medium brown with whitish tip and whitish ribbing on outer web of R6; whitish marbling and barring basally on outer rectrices best seen when tail fully spread or from below. IN FLIGHT: pale brownish to creamy overall with variably darker, medium brown to pale brown outer webs to P7-P10 and broad, medium brown to pale brown distal tail band; inner secondaries sometimes slightly darker than upperwing coverts; wing-linings medium to pale brownish. Eyes dark, bill blackish, usually with variable dull flesh on basal two-thirds by early winter and sometimes flesh pink with fairly clean-cut blackish tip; legs flesh pink to flesh. 1st pre-alternate molt (Oct.—Apr./May; does not include upperwing coverts) produces first alternate plumage. Note that some birds retain most or all juvenal plumage through Apr. and May and look bleached white overall. Head, neck, chest, and flanks variably mottled and streaked smoky grayish. Al scapulars range from whitish to pale grayish, typically with fine, often blurry, darker bars or wavy markings that contrast with bleached brownish markings of juvenal scapulars. Bill typically blackish with dull flesh to flesh pink basally; legs flesh pink; eyes dark.

Second Cycle. Complete 2nd pre-basic molt  (May/June-Sept./Oct.) into second basic plumage. Some birds bleach strikingly by early summer, before 2nd pre-basic is very advanced—and new 2nd basic feathers can look contrastingly dark. Head, neck, and underparts white, variably mottled and streaked gray-brown; head and chest of some birds bleach to mostly whitish by mid-winter. Upperparts vary from whitish with diffuse, fine, and fairly sparse brownish barring and speckling to extensively but finely barred and checkered brown; some birds have a few gray back feathers and others have a mostly pale gray back. Tertials whitish with variable brownish speckling and barring, to medium-pale gray-brown with speckled and notched whitish tips and edging. Wingtips medium gray-brown to whitish, not contrastingly darker than tertials. Upperwing pattern of remiges similar to first cycle, but inner primaries average paler and secondaries darker and grayer; outer primaries of darker-winged birds often show whiter tongues (and sometimes a faint P10 mirror) hinting at adult pattern. Distal tail band medium to pale gray-brown, often with more-extensive and finer whitish basal markings than first cycle; tail mostly whitish on palest birds. Wing-linings medium to pale gray-brown with underside of primaries often reflectively pale and showing a ghosting of upperwing pattern. Eyes pale lemon to brownish, bill typically flesh pink to pale greenish with black distal third and pale horn tip (sometimes duller, like first winter), legs flesh pink. Partial 2nd pre-alternate molt (Sept.-Apr.) often includes some upperwing coverts) produces second alternate plumage: head, neck, and underparts whiter, variably mottled dusky (sometimes bleaching and wearing to mostly white by summer), back more extensively gray in contrast to faded upperwing coverts; some birds attain a few gray upperwing coverts, especially median coverts. Orbital ring can be pinkish in summer. By summer, some birds have yellowish bill with reddish gonydeal smudge and black distal band.

Third Cycle. Complete 3rd pre-basic molt (May/June-Oct.) produces third basic plumage. Head, neck, and underparts white with variable dusky streaking and mottling. Upperparts pale gray, usually with variable brown wash to upperwing coverts, brownish tertial centers. Rump and tail white with variable pale brownish distal tail markings (tail varies from all white to having a fairly broad, pale brownish band). Variable wingtip patterns mirror adult patterns (see above) but darker-winged birds have more-extensive grayish (to brownish gray) and less white than adult. Underwings mostly white with variable brown markings on coverts, outer primaries show ghosting of upperwing pattern. Eyes pale lemon to brownish; bill flesh to dull pale greenish with black distal band and pale tip; legs flesh pink. Partial 3rd pre-alternate molt (Sept.-Mar./Apr.) into third alternate plumage: dark markings on head and neck reduced to absent; bill brighter and can be indistinguishable from adult or have dark distal marks. White tips to outer primaries may be lost by wear. Adult plumage attained by complete 4th pre-basic molt (May/June-Oct./Nov.).

SIMILAR SPECIES

In ne. N. America, the main confusion species are Glaucous Gull, Iceland Gull, and Thayer’s Gull; also see hybrid Glaucous Gull x American Herring Gull. Other potentially similar species and hybrids occur mainly on the Pacific Coast of N. America (see Rarer Species).

Adult Cycle. GLAUCOUS GULL (n. latitudes) larger overall with longer and stouter bill, longer legs, and relatively shorter wing projection; upperparts paler gray (Kodak 3-4 in e. N. America) and wingtips all white. Bill often more pinkish based in winter and with dark distal marks; eyes pale lemon, orbital ring yellow-orange to reddish (can be pinkish in winter).
THAYER'S GULL (winters mainly on Pacific Coast of N. America) averages larger with longer and more hook-tipped bill, slightly longer and more pointed wing projection. Wingtip markings slaty blackish (Kodak 14.5-17) and often more extensive (on 5-6 outer primaries), upperparts slightly darker (Kodak 5-6). P10 and P5 can have complete dark subterminal bands, P9 mirror often restricted by continuous dark along the outer web, and slaty blackish medial area on P9 typically extends on to inner web. Presumed hybrids with Kumlien’s look intermediate and not safely assigned to either taxon.
ICELAND GULL (apparently rare in N. America) similar in size and shape but averages paler upperparts (Kodak 3-4) and has all-white wingtips, pale lemon eyes. May interbreed with Kumlien’s Gull, so some individuals not safely assigned to either taxon. An evaluation of variation in upperpart tone, wingtip pattern, eye color, and orbital ring color of adult Iceland Gulls is desirable; until then, field separation criteria from pale-winged Kumlien’s should be considered tentative.
HYBRID GLAUCOUS GULL X AMERICAN HERRING GULL (widespread) best told by larger size and structure, especially longer and stouter bill, longer legs; birds with Glaucous Gull structure also have short wing projection. Bill often more pinkish based in winter and with dark distal marks. Orbital ring in summer yellow-orange (can be pinkish in winter). Critical study of wingtip patterns needed.

First Cycle. See adult cycle for structural differences between taxa.
GLAUCOUS GULL differs in larger size and structure, white to whitish wingtips, flesh pink bill with clean-cut blackish distal third.
THAYER’S GULL darker and browner overall with blackish brown to dark brown wingtips (with strong inner web/outer web contrast on P6-Pl0), dark secondary bar and tail, and more solidly and darker brown tertials. Presumed hybrids with Kumlien’s look intermediate and not safely assigned to either taxon.
ICELAND GULL perhaps not safely separable from palest-winged Kumlien’s. Iceland typically has evenly pale (whitish) primaries versus brown-washed outer primaries (especially
outer webs) and whitish inners on Kumlien’s - but bleaching by midwinter can render such distinctions moot. Iceland more often attains a distinct pinkish bill base in first winter, but a few Kumlien’s overlap in this feature.
HYBRID GIAUCOUS GULL X AMERICAN HERRING GULL best told by size and structure, especially bill; often has Glaucous-like pinkish bill with black tip and Herring-like darker secondary bar.

Second Cycle. See adult cycle for structural differences between taxa.
GLAUCOUS GULL differs in larger size and structure; primaries evenly whitish without darker outer webs to outer primaries.
THAYER’S GULL averages longer bill and longer and more-pointed wingtips; its darker wingtips have distinct dark outer webs to P6-P10, and P5 often has a large dark distal mark
(dark outer webs usually restricted to P7-P10 on Kumlien’s). Presumed hybrids with Kumlien’s look intermediate and are not safely assigned to either taxon.
ICELAND GULL perhaps not safely separable from palest-winged Kumlien’s but typically
has evenly pale (whitish) primaries versus brown-washed outer primaries (especially outer webs) and whitish inners on Kumlien’s.
HYBRID GLAUCOUS GULL X AMERICAN HERRING GULL best told by size and structure, especially bill.

Third Cycle. Glaucous Gull, Thayer’s Gull, Iceland Gull, and hybrid Glaucous Gull X
American Herring Gull all differ in much the same ways as do adults (see above and relevant species accounts).

RARER SPECIES

All of these N. Pacific hybrids can resemble Kumlien’s Gull in plumage, but all are larger and differ in structure. Also see Glaucous-winged Gull (differences noted under that species).

Adult Cycle. HYBRID GLAUCOUS-WINGED GULL X AMERICAN HERRING GULL (w. N. America) larger and bulkier overall with a bigger bill; some have broader wings with shorter wing projection (more like Glaucous-winged), orbital ring can show some yellowish (like Herring), and bill in winter often has dark distal marks. Study needed of wingtip patterns.
HYBRID GLAUCOUS-WINGED GULL X GLAUCOUS GULL (Pacific) larger and bulkier overall with a bigger bill, broader wings with shorter wing projection. Orbital ring may show some yellow-orange, and bill  in winter often has dark distal marks. Study needed of wingtip patterns.
HYBRID GLAUCOUS-WINGED GULL X WESTERN GULL (w. N. America) larger and bulkier overall with a bigger bill, broader wings with shorter wing projection, and darker upperparts (Kodak 6-8). Orbital ring may show some yellow-orange, and bill in winter often has dark distal marks. Study needed of wingtip patterns.

First Cycle. See adult cycle for structural differences between taxa.
HYBRID GLAUCOUS-WINGED GULL X AMERICAN HERRING GULL best told by size and structure; more often has darker secondary bar and tail.
HYBRID GLAUCOUS-WINGED GULL X GLAUCOUS GULL best told by size and structure, especially large bill, short wing projection.
HYBRID GLAUCOUS-WINGED GULL X WESTERN GULL best told by size and structure, especially large bill, short wing projection.

Second Cycle. See adult cycle for structural differences between taxa.
HYBRID GLAUCOUS-WINGED GULL X AMERICAN HERRING GULL best told by size and structure; more often has darker secondary bar and tail.
HYBRID GLAUCOUS-WINGED GULL X GLAUCOUS GULL best told by size and structure, especially large bill, short wing projection.
HYBRID GLAUCOUS-WINGED GULL X WESTERN GULL best told by size and structure, especially large bill, short wing projection.

Third Cycle. Hybrids all differ in much the same ways as do adults (see above).

HYBRIDS

Presumably with Thayer’s Gull [Gaston & Decker, 1985; Knudsen, 1976] but extent of hybridization difficult to assess (see Taxonomy and introduction to Iceland Gull complex); seems possible with Iceland Gull in w. Greenland [Boertmann, 2001].

Banded birds

Iceland Gull (kumlieni) A4 adult, January 2013 - March 2015, Quidi Vidi Lake, St. John's, Newfoundland. Picture: Lisa de Leon, Peter Adriaens & Alvan Buckley.
Iceland Gull (kumlieni) C0 adult, December 24 2014, Quidi Vidi Lake, St. John's, Newfoundland. Picture: Alvan Buckley.
Iceland Gull (kumlieni) C8 adult / 4CY?, December 03 2014, Mundy Pond, St. John's, Newfoundland. Picture: Les Sweetapple.
Iceland Gull (kumlieni) F6 adult, December 2013 - January 2015, Quidi Vidi Lake, St. John's, Newfoundland. Picture: Lisa de Leon & Alvan Buckley.
Iceland Gull (kumlieni) H6 adult, January 2015, December 2016 & January 2017, Quidi Vidi Lake, St. John's, Newfoundland. Picture: Chris van Rijswijk, Lancy Cheng, Lisa de Leon & Alvan Buckley.
Iceland Gull (kumlieni) H8 1st-5th cycle (2CY-5CY), 2013-2016, Quidi Vidi Lake, St. John's, Newfoundland. Picture: Peter Adriaens, Lancy Cheng & Alvan Buckley.

White outer primaries

Iceland Gull (glaucoides) adult, December 15 2007, Fraserburgh, Scotland. Pictures: Chris Gibbins. Primary: Stage 0. Iris: class 1 (0%>1% speckling). Classic bird.
Iceland Gull (glaucoides) adult, November 02 2008, Fraserburgh, Scotland. Pictures: Chris Gibbins. Primary: Stage 0. Iris: class 1 (0%>1% speckling). Classic bird.
Iceland Gull (glaucoides) adult, December 2011, St John's, Newfoundland, Canada. Picture: Dave Brown.

Patterned outer primaries

Kumlien's Gull (kumlieni) adult, 3 birds, St John's, Newfoundland, Canada. Picture: Dave Brown.
Kumlien's Gull (kumlieni) adult, December 04 2014, Lake County, IL. Picture: Amar Ayyash.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's Gull (kumlieni) adult, December 28-29 2012, Bluffers Park - Toronto. Picture: Declan Troy.
Kumlien's / Thayer's Gull (kumlieni / thayeri) adult, December 18 2011, Canal Park, Duluth, MN. Picture: Karl Bardon. This bird lacks a dark sub-terminal band on P5 and has only two extremely small dots on P6 (and only on the right wing, not such on the left wing), which would be odd for Thayer's. But note that the outer-web of P9 is completely covered by black, reducing the mirror on P9 to only the inner-web, which would be odd for Kumlien's.
Kumlien's / Thayer's Gull (kumlieni / thayeri) adult, December 18 2011, Canal Park, Duluth, MN. Picture: Karl Bardon. The white mirror on P9 reaches the outer edge on the outer-web as in Kumlien's. But note the thin subterminal band on P5, the dark blackish extending along the outer-web of P10 all the way to the primary coverts, medial black on the inner-web of P9 and the rather coarse head and bill structure (all more typical of Thayer's).
Kumlien's / Thayer's Gull (kumlieni / thayeri) adult, December 17 2011, Canal Park, Duluth, MN. Picture: Karl Bardon. Although the white mirror on P9 reaches the outer edge on the outer-web as in Kumlien's, note the black dot on the outer-web of P5, the dark blackish extending along the outer-web of P10 all the way to the primary coverts, and the rather coarse head and bill structure (all more typical of Thayer's).