glaucoides & kumlieni

(last update: October 12, 2011)

Iceland & Kumlien's Gull 2cy January - February

By mid-winter, many birds are still in juvenile plumage with the feather fringes slightly worn and the patterns often bleached to pale buffish. Below, we copy the paragraphs on Iceland Gull from Gulls of North America, Europe, and Asia, by Klaus Malling Olssen & Hans Larsson (see this guide for more images and plates).

IDENTIFICATION
Length 52-60 cm, wingspan 140-150 cm. A medium-sized arctic gull, smaller than Herring and Glaucous Gull with smaller, more rounded head, larger eyes and shorter, weaker bill. The first impression is of a large gull with the head of Common Gull! The breast is deep and the rear accentuated, as the long wings reach several cms beyond the tail (equivalent of bill length or longer). The legs are short, with little of tibia visible. Large males have more sloping forehead, heavier bill and proportionately shorter wings. Although sometimes approaches Herring Gull in size, it lacks latter’s brute masculine look. In flight elegant with slender wings (hand clearly longer than in Glaucous), short, rounded head and deep breast. Handles hard winds well, and may perform much shearwatering in hard head-winds. Often feeds agilely, snapping up food directly from sea. See Glaucous Gull for further differences and treatment of ID from that species.
Two forms: Iceland Gull nominate glaucoides (in plumages almost identical to Glaucous Gull) and Kumlien’s Gull kumlieni, which is thought to have evolved from hybridisation with Thayer’s Gull (Dwight 1925, Weir et al. 2000). Kumlien’s is a highly variable taxon with hardly any two birds being identical, giving meaning to treating it as a hybrid population appearing over a very wide zone - probably with a narrow hybridisation zone with glaucoides to the East and Thayer’s Gull to the West. It is suggested that its name should be put in brackets (Yésou 2002). While we fully agree with the explanation of its origin, we maintain to treat kumlieni as a valid taxon, given its often distinct plumage, while this from a taxonomic view may be considered dubious, it seems better from an ID point of view.

Juvenile /first-winter glaucoides similar to Glaucous Gull, but the shorter bill has broader black tip grading into paler base. The base may be fleshy, but not the bubblegum-pink of Glaucous. Plumage generally greyer, and head often with pale hind-collar against dark shadings above and behind eye.
Palest kumlieni identical. Many kumlieni however identifiable by combination of black bill and dark leading edge to outer primaries (rarely dark trailing edge similar to Thayer’s Gull and many Sterna terns). When settled, pale-fringed primaries often slightly darker than upperparts and at least some primaries have dark V-markings (sometimes restricted to inner ones, unlike Thayer’s Gull – J.R. King in litt.). Some have darker outer webs to P6-10, creating vague ‘venetian blind’ pattern, others have rather plain brown-washed primaries, concentrating along the shafts. (Glaucoides has much paler primaries, these typically being the palest part of the bird and only rarely with indistinct dark V-markings.) Some kumlieni show slightly dark outer webs of primaries, but markings are coarser, and their overall paleness suggests a very pale gull. With wear, outer primaries may lose dark markings and appear whitish, thus similar to glaucoides. Tail in kumlieni often with dark-shaded sub-terminal bar, matched by darkest nominate, which normally has pale, faintly mottled tail or several narrow sub-terminal bars. Head and body of kumlieni often darker greyish; normally paler buffish in glaucoides.

Geographical Variation: Kumlien’s Gull kumlieni

Juvenile/first-winter kumlieni highly variable. Pale birds inseparable from glaucoides, dark birds very similar to certain Thayer’s Gulls. Many darker greyish-brown with more solid dark markings than any glaucoides, especially on wing-tip. From extensive study (skins, photos and live birds, Greenland and N Atlantic - Zimmer 1991 Garner et al. 2000, B. MacTavish in litt.). Characters indicating kumlieni from nominate glaucoides are:

• Medium greyish-brown outer webs and dark sub-terminal markings to P6-P10, from below creating brownish trailing edge. From above, dark outer webs create darker outer wing than in glaucoides, appearing concolorous with inner wing and typically plain, with brown wash centred along primary shafts, spreading onto both webs, generally darkest on middle part of outer web. The darkest birds show pale brown or grey primaries with pale tips as in Thayer’s Gull, but often with pale covering edges, not just tips as in Thayer’s, which typically has inner primaries paler than outer primaries (as broad window). Many have dark V-markings on wing tip, sometimes on all primaries, but in paler birds restricted to P1-P5. Glaucoides has primaries paler than rest of upperparts, often uniform (but this seen in worn kumlieni from midwinter), and at most with weak dark chevrons. May show narrow but distinct dark sub-terminal crescents on inner primaries as in juvenile Calidris waders. Sometimes P1-P5 slightly paler than P6-P10. Note that from mid-Feb brown primary wash of most kumlieni disappears, leaving outer wing very similar to average nominate.
• Normally pale brownish-grey tail-bar or tail-centres with pale mottling on T4-T6 (rarely T1-T3), at bases of most or all rectrices and darker internal markings on midtail; tail-bar contrasts with paler, dark-barred uppertail-coverts. Dark tail-bar present in 15% glaucoides, in 80-95% kumlieni (Zimmer 1991, pers. obs.). Tail-bar of kumlieni 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.
• Stronger greyish tinge to generally darker, denser-patterned head and body, including broader, darker spots or sub-terminal crescents on mantle, scapulars and sometimes wing-coverts, sometimes forming irregular pattern. Thayer’s typically darker with broader dark eye-mask and longish-looking lores.
• Most kumlieni have black bill with slightly paler brown base, but this becomes gradually paler by midwinter. Small minority have bicoloured bill with pale inner 60%. Most glaucoides have bicoloured bill, some pale with black tip, small minority black-billed.
• Tertials sometimes medium brown with pale spotting or mottling along edges; intermediate between nominate and Thayer’s Gull. Glaucoides (and many kumlieni) have pale tertials with narrow brown bars. In Thayer’s tertial centres more solid mud-brown, recalling pattern of American Herring Gull.
• Darkest birds have slightly darker secondaries in contrast to pale inner primaries and coverts. In Thayer`s Gull, contrast is stronger, in nominate absent.
• Primary projection probably never as grotesquely long as in many glaucoides.

Moult into first-winter generally more advanced compared to glaucoides, mantle and scapulars from Oct/ Nov. Fifteen Newfoundland birds Jan-Feb had renewed 10-80% of scapulars, most 40-60% (B. Mactavish in litt.).

Description
Juvenile (fledging—(Dec)Mar) Head light brownish-grey to greyish-buff, fading to whitish on chin, forehead and hindneck. Brown streaks fine and inconspicuous, but sometimes denser above eye and neck, creating pattern similar to washed-out winter Black-headed Gull. Eye-crescent dusky. May show inconspicuous whitish crescents above and below eye, but only rarely pale eye-ring.
Mantle, scapulars, tertials and upperwing-coverts pale greyish to buff with intricate brownish bars, marbling or V-shaped spots, strongest on lower scapulars and greater coverts; on average neater and denser than in Glaucous (especially on distal part of tertials); pale birds have weak, scattered markings.
Primary coverts often slightly darker with pale edges and narrow dark sub-terminal markings near tip. Rump white with brown bars; in many paler than in Glaucous. Primaries and secondaries grey-brown to whitish-buff (concolorous with or paler than upperparts) with broad paler tips, forming pale wing-tip in settled birds; often with narrow dark chevrons near tip (generally more prominent than in Glaucous). Shafts white to pale yellow. The darkest-patterned birds may show darker grey outer web to P6-P10 and slight pale edge to tips of P6-P10 (often together with darker-than-average plumage and more solid dark on tail - intermediates with kumlieni?).
P10 6-12mm > P9. Tail pale grey or buff with variable amount of dark marbling or diffuse pattern, several grey sub-terminal bars or one broad grey sub-terminal bar, bordered by white tips and tail-sides. Some have stronger dark barring on outer tail than any Glaucous, barely different from rump-barring.
Underbody brownish-grey to buff with faint dark barring on breast-sides and flanks; belly often darkest. Small minority with denser dark spots on whole underbody. Undertail-coverts pale with pale brown bars. Axillaries and underwing-coverts greyish-brown with indistinct dark mottling contrasting with pale flight feathers; greater coverts often paler and greyer than lesser/ median.
Iris dark brown.
Bill variable: in <2% whole bill is blackish, but normally with paler (dark brown to grey-brown, greyish-yellow or olive-grey) basal 30-45%; in <5% the basal region is fleshy or pink. Division from black tip normally more diffuse than in Glaucous, with black penetrating along cutting edges. Precise bill pattern may be hard to judge according to darkish coloration of base; birds with pale bill patterned more like Glaucous. Gape flesh. At fledging, bill generally darker.
Legs pale flesh, at fledging often with slight grey cast, especially around knee. Legs then generally darker than in Glaucous Gull (C. Johnson in litt.).

First-winter (Oct-May) Most retain juvenile plumage; birds renewing parts of plumage have head and body (especially hindneck) paler, in some almost whitish. If renewed, new mantle to scapulars whiter with coarser, more irregular barring. From Jan/Feb most fade to whitish apart from scattered brownish feathers. May develop pale bill-tip from Mar (rarely late Dec).

2cy glaucoides in Europe

outer primaries as dark as inners: kumlieni