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"The Herring Gull Assemblage" in South Korea.
Nial MOORES, January 2003.
Introduction:
This paper is a work in progress, based especially on field experience by the author of
"The Herring Gull Assemblage" in southwest Japan and South Korea in every winter between
1990 and the present. It presents the main forms considered to occur in South Korea,
summarizing selected identification criteria of especially juvenile/first winter
and winter adult plumages and suggests their distribution within the country: information at
present largely unavailable to "gullers". The proposed identification criteria (highlighted by images
taken within South Korea) and discussion on taxonomic decisions, aims to elicit considered
responses from other "gullers", both within and outside of the region, so that after further
revision the paper can then be submitted to an appropriate medium for publication
(with all contributions fully acknowledged).
In its present form, it already expands on descriptions included in The Birds Of South Korea (a video produced by C. Moores and NM), and adds a ’Korean perspective’ to the ground-breaking
paper on gull systematics published in the Hong Kong Bird Report by Kennerley et al
(1995), and especially to two excellent papers recently published in Dutch Birding
(Yesou 2001; Yesou 2002). All three papers contain extensive reviews of the literature and
details of museum specimens and nesting colonies (elements which fall outside of the scope of
this paper), but do not provide necessary details on juvenile or first winter plumages, or
examples of several apparently identifiable forms regularly observed in Korea. Over 9000 words long and containing 37 images, this paper has been split into three pages to make downloading faster. Sections can be accessed by clicking on the links below:
Page 1:
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"The Herring Gull Assemblage" in South Korea.
 Vega Gull (left), Taimyr Gull (centre), Mongolian Gull (right). Photos taken in December - February, © Charlie MOORES and KIM Hyun-tae.
Taxa belonging to the "Herring Gull Assemblage" (a term apparently coined by de Knijff et al) pose one of the toughest identification challenges in South Korea, even though several
forms appear to be widely distributed in winter. Although only ca 400km north-south and roughly
the same west-east, the country’s coastline is long and varied (with extensive tidal-flats and wide
bays with numerous indentations and offshore islands along the west coast, the eastern flank
of the Yellow Sea; deeper bays with narrower estuaries and widespread industry along the south
coast; and a mix of rock and sand beaches with deep sea fishing harbors along the east coast),
and a visit to almost any river-mouth, beach or harbor in winter provides the birder with a fairly
bewildering range of gulls.
"Phenotypic variation and systematics of Mongolian Gull" (Yesou, 2001), and "Trends in
systematics" (Yesou 2002) are both extremely well-researched and useful papers in helping
consider this complex, with the former documenting the appearance and measurements of breeding
Mongolian Gull at sites on Lake Baikal, and the latter offering a summarized presentation of all of the "taxa of the Larus argentatus-cahninnans-fuscus complex, intending to propose a reappraisal of their classification" (Yesou, 2002). Both papers concentrate on describing the (breeding-plumage) adult forms of the various taxa, most particularly their mantle colour, primary patterning and leg colour, as well as summarizing the results of recent mtDNA studies and other information on breeding behavior and distribution. This leads to Yesou’s reappraisal of the various taxa, and some suggested changes in nomenclature.
Before further considering the taxonomic arrangement presented by Yesou (2002) it is
necessary to describe in some detail the typical appearance and distribution of the main forms
of the Herring Gull Assemblage found in South Korea,
namely those which are generally being called Vega, Taimyr and
Mongolian Gull(from hereon termed the Assemblage). Each account describes the
taxon’s distribution in South Korea in general
terms, the overall structure of the forms (which is considered a useful
though rather variable feature, Ujihara in lit., pers obs), and then
concentrates on the appearance of juvenile/first winter and winter adult
plumages. The taxonomy of the forms will be further discussed after the
descriptions. Vega Gull, including Birula Gull
 Image 1: Vega Gulls, Pohang, February. Photo © Charlie MOORES
This is generally considered to be the most widespread and numerous of the group occurring in
South Korea (and also Japan). If birulai is included, it is also probably the most
variable in appearance. Main autumn arrivals take place in mid- to late October, with significant
numbers remaining through the winter (concentrations of 1 000 plus occur at several sites,
even in December and January). Most northward movement appears to take place from
perhaps mid-February, through March. Only small numbers remain into April and early May.
Structure
Plumage
 Image 3: 1st W Vega Gull, January Photo ©KIM Hyun-tae. Image 3: First winter Vega Gull, January. Pale and long-winged, this perhaps appears structurally closer to birulai than vegae. Note the barred greater coverts, notched and relatively intact tertials, and the broad blackish tail band.
Paler birds (perhaps largely attributable to northernmost populations or birulai?) can be
somewhat suggestive of a pale Thayer’s Gull L. thayeri, being a light grey-brown tone
with grey-brown concentrated around the eye; obvious, clean looking fringes to
the mantle and wing coverts; and obviously notched, dark-centred tertials. They show
obvious barring across all of the greater coverts, which often bleach paler still by mid-winter and
appear very worn by February. Many of these paler birds appear somewhat lightly built.
 Image 4: 1st W Vega Gull (with 2nd W Slaty-backed Gull), January. Photo ©KIM Hyun-tae Image 4: First winter Vega Gull, January. Rather coarsely marked and dark, this ill-proportioned individual perhaps appears structurally closer to vegae. Progressively darker birds can be much more suggestive of American Herring Gull. They have a dark brown sludgy look to much of the underparts (through until Dec-Jan), though even by October/November this is usually relieved by a rather pale and more spotted vent and undertail coverts, and a somewhat paler forehead, lores, chin and throat. The upperparts are also rather more darkly marked, with dark centers to the scapulars and often more solidly dark tertials on the closed wing which show a broad whitish fringe variably marked with brown "notches".
In flight, first winters show a very dark, contrasting secondary bar and a fairly weak pale blaze across the inner primaries (not as strong as depicted in Lee, Koo and Park, 2000). They also have a notably light brown (or even whitish) rump and barred or spotted uppertail coverts, which contrast strongly with a typically narrowly white-based blackish tail (though some birds can appear to show a significantly narrower black tail band, rather closer to Mongolian). The outermost tail feathers can often show pale and dark "laddering", especially basally. The underwing tends to appear rather plain and brownish. Interestingly, a very few show a dark bar across part of the greater coverts: this could be intra-taxon variation within Vega, misidentification of extralimital American Herring Gull, or a result of hybridization, between either Vega, Heuglin’s, Mongolian, Slaty-backed or American Herring Gull. Most show largely dark bills with some dirty dark pink basally, which becomes increasingly obvious by ca January.
 Image 5: First Winter gull showing mixed/unclear characteristics, December Photo ©Nial MOORES. Image 5: First winter, December. Individual showing several characteristics suggestive of smithsonianus, including a wholly blackish tail (with only laddered white outers), a strikingly dark bar across part of the greater coverts, long primary projection beyond the tail and notched tertials.
Winter adults appear rather dirty, with dark grey lead-toned upperparts; some, though, are distinctly paler-looking, and have generally been considered to be Birula Gull (following Kennerley et al, 1995 and Hoogendoorn et al 1996). Such birds show a rather icier-looking tone to the grey of the upperparts, and structurally look closer to the birds considered to be Taimyr Gull, in that they appear rather neat and compact; show rounded-looking heads and flattish-backs; a slightly longer primary projection; and a cleaner pink tone to the legs. In addition, they tend to have rather finer head streaking, without the smudgy look of most Vegas. They are scarce in South Korea, constituting probably less than 1 in 250 individuals.
 Image 6: Adult Birula Gull, Song Do, February. Photo © Charlie MOORES.
Image 8: Adult Birula Gull, January. Although most birds showing "mixed characters" are generally considered to be taimyrensis x vegae/birulai hybrids, this bird (showing coarse head markings extending to the breast sides approaching vegae, but a more compact and neat structure suggesting taimyrensis) apparently also has a paler mantle than either. According to Yesou (2002), this should therefore be identified as a yellow-legged Birula Gull.
According to Yesou (2002), there is little variation in mantle coloration of
Vega Gull, though he states that the northernmost populations (nesting on the New Siberian Islands, which lie within the range ascribed for birulai) are the palest-mantled, while the westernmost and easternmost are the darkest. Most birds presently considered birulai presumably therefore refer to these more northern populations (see discussion section below). In mid-winter (December-January) most Vega show extensive grey-brown (tinged warmer) streaking and smudged "thumbprints" on the hindneck, across the neck sides, and often down the breast sides, with the most extreme looking hooded like Thayer’s or American Herring Gull. In ca 150 Vega checked in one flock in mid-January 2003 ca 1 in 4 or 1 in 5 looked hooded, with 2 individuals very darkly so.
 Image 9: Adult Vega Gull, January. Photo © KIM Hyun-tae. Image 9: Adult Vega Gull. A rather long-winged, deep-chested and powerful individual.
The majority show obvious dark markings up onto the crown and around the eye, though
smaller numbers show much weaker head markings, with most markings concentrated on the lower nape.
The majority of adult Vega Gull have largely dark eyes in winter, with the darkest
looking solidly dark brown in the field. Around 50 out of 100 checked in mid-December
2002 looked dark-eyed, with ca 20 intermediate and 30 pale, while by mid-January
2003 (at a different site) ca 80 out of 100 looked dark-eyed, with ca 15 intermediate-pale,
and only 2 clearly yellowish or whitish. All appear to show a deep red eye-ring.
Bill colour of adults in the same mid-winter period is typically weak yellow, with an
orangey-red gonys spot, and only occasional small blackish marks on the bill (that are seldom
as extensive as on some Mongolian).
Taimyr Gull or taimyrensis
 Image 10: Winter adult Taimyr Gull (rear) and Vega Gull, January. Photo ©KIM Hyun-tae.
This taxon, generally considered to be the eastern subspecies of Heuglin’s Gull
(e.g. Kennerley et al. 1995, Hoogendoorn et al. 1996), is fairly widespread in South Korea,
especially in autumn and perhaps again in early spring, usually occurring in small
concentrations of 3-5 or less per ca 100 Vega Gulls in mid-winter. It apparently arrives
in the northern Yellow Sea in mid-September (Dierschke and Heintzenberg, 1994), with
small numbers appearing in South Korea at the same time. Numbers apparently peak
sharply in mid-October, when for example in 2002 ’pure’ flocks of 15-30 birds (comprising
both adults and juveniles/first winters) occurred offshore from the west coast (somewhat
contra the account in Birds of South Korea). Becoming scarcer in mid-winter, numbers
apparently then increase again in February and March, suggesting that many individuals
winter south of Korea: a suggestion supported by Kennerley et al. (1995), who consider it
the most numerous taxon of the Assemblage in Hong Kong. Structure What are considered "typical" Taimyr Gulls appear neat and fairly compact, with short to medium length legs, shortish bills showing a weak gonydeal angle, and a rounded head shape. Compared with Vega they tend to look rather flat-backed and in direct comparison are usually smaller. They show a slightly longer primary projection beyond the tail, and appear longer and more narrow-winged in flight.
 Image 11: Adult taimyrensis, December. Photo © KIM Hyun-tae. Plumage
Juveniles and first winters are strongly suggestive of (western forms) of
Lesser Black-backed Gull L. fuscus graellsi, in that they appear rather dark,
with solidly dark tertials showing no notching and only a narrow white fringe - which unlike
Mongolian Gull’s are not prone to obvious wear early in the winter. In addition, they show an
obvious dark band across the (outer) greater coverts. The brown tones overall are rather
cleaner than those found in Vega (lacking any grey) and often include some rustiness on e.g.
the hind neck and juvenile scapulars.
 Image 12: 1st W Taimyr Gull (with winter adult Vega Gull), January. Photo © KIM Hyun-tae. Image 12: First winter Taimyr Gull, January. Structurally distinct, note the rather dark greater coverts, the rusty tones to some feather centers and edges, and the largely dark bill.
 Image 13: 1st W Taimyrensis, February. Photo © Charlie MOORES.
In flight, first winters show further similarities to Lesser Black-backed Gull: they lack an obvious blaze on the base of the inner primaries; show a blackish secondary bar and a dark (though not black) bar across the greater coverts; and have a rather more obvious white rump and whiter bases to the tail feathers than shown by Vega. So-called "typical" winter adults (which at most comprise probably less than half of the birds presently being called taimyrensis in Korea, the rest often being considered taimyrensis-vegae hybrids) have dark grey upperparts (i.e. more slaty and slightly darker than Vega and most Mongolian) and pinky-yellow, yellow or bright yellow legs.
 Image 14: Winter adult Taimyr Gull (right) with two winter adult Vega, January. Photo © KIM Hun-tae./font> Image 14:Winter adult Taimyr Gull. Note the smaller size than vegae of this rather long-legged individual, and the extent of head streaking (much more extensive than shown by any Mongolian Gull types photographed at the same time of year).
The primary moult of many typically appears to be later than in Vegaor Mongolian (though the range in these taxa is perhaps not yet
fully understood), with many still in active moult in December, by which time they also
show fine streaking concentrated on the hindnape and around the eye, which itself is paler
and yellower than most Vegas’. The bill is typically rather brighter than other taxa, with an obvious orangey-red gonys spot bleeding on to the upper mandible. Most show some dark
markings near the gonys spot and a rather paler tip. Heuglin’s Gull Looking at the descriptions of nominate heuglini found in Grant (1986), Kennerley et al. (1995) and elsewhere, and comparing them with the range of the taimyrensis found in South Korea, it appears that nominate Heuglin’s Gull also occurs occasionally in South Korea (and neighboring Japan), with 3-4 observations of adults and and one suspected juvenile/first winter made by the author between 1998 and 2002. Though the adults appeared rather similar in coloration to some smaller taimyrensis, their head-streaking was more spotty and more confined to the hind-nape, and they showed striking structural differences: obviously more massive and powerful, with significantly longer legs. Interestingly, in interactions with other gulls (including Vega and Slaty-backed) they appeared both aggressive and dominant.
One possible first winter (photographed in December 2002) also appeared long-legged, very heavy billed and colder in plumage tones than taimyrensis, more suggestive of Great Black-backed Gull L. marinus than Lesser Black-backed Gull.
Image 17 and 18: Suspected juvenile nominate Heuglin’s Gull Larus heuglini heuglini (front bird) with juvenile/first winter Slaty-backed Gull Larus schistisagus (rear bird). Busan, November 2002. Photos © Nial MOORES Image 17 and 18: "Juveniles very similar to this are very often found in east Japan in autumn/winter" and are considered likely to be late-molting mongolicus (Ujihara in lit.). Similar to some darker mongolicus, this individual however shows a dark outer greater covert bar, a largely dark tail, and lacks the coarse hind-nape markings considered by the author more typical of that taxon.
Baraba Gull or barabensis Considered either a distinct species or a subspecies of Heuglin’s Gull (Yesou, 2002), barabensis-type individuals have been observed in Korea one or two times, with one photographed by A. Van Den Berg and M. Robb in October 2002.
 Image 19: Suspected Baraba Gull (left), October. Photo © Arnoud van Den BERG
Image 19:This individual is included here as it appeared much more elongated and rather darker on the upperparts than typical taimyrensis, completely lacked head-streaking (unusual, but not exceptional for taimyrensis at this time of year), and showed a similarly weak scapular crescent to the depiction of summer barabensis in Yésou (2002). However, its identification remains unclear, due to uncertainties about the range in appearance of barabensis, including the extent of dark markings on the bill, and taimyrensis. Although structurally distinctive, this individual is considered by Ujihara (in lit.) to fall within the range of summer taimyrensis.
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