Larus cachinnans

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3cy cachinnans: February

Phenotypic variation and systematics of Mongolian Gull

IN: Dutch Birding 23: 82, 2001 BY: Pierre Yésou

PART 1: INTRO & DISTRIBUTION
BELOW: PART 2 PHENOTYPIC VARIATION

Phenotypic variation

The original description of mongolicus by Sushkin (1925) is as follows: ’Above as vegae [Vega Gull L. vegae], darker than cachinnans ([from] Kirghiz steppe and Lake Zaissan), feet pink, orbital ring vermilion-red; grey wedges of the inner webs of primaries shorter and darker than in cachinnans but lighter than in vegae. Wing male 462-480, female 442-450, tarsus 65-70, middle toe 52-38. From 8 specimens, South-Eastern Altai and NW Mongolia. Type: male ad., 9.VII.1914, Lake Uring-noor, NW Mongolia' (Sushkin’s descriptions of new taxa are both in Russian and English).

Further details were given by Stegmann (1934). He studied 27 skins of adult birds and mentioned a wing-tip pattern darker than in cachinnans and closer to Birula Gull L. v. birulai, with black on the seven or eight outermost primaries and a subterminal black bar on p10 (primaries are numbered ascendently). The latter taxon was given the name birulai (Pleske 1928), in honour of the great sailor and Arctic explorer Birula, hence the male gender. Regrettably, many authors kept using the name ’birulae’, a misspelling by Stegmann (1934). Birulai is hardly differentiated from vegae, except for the variable leg colour and darker iris in some birds. It is treated as either a synonym of vegae or a subspecies of it (eg, Stepanyan 1990, Kennerley et al 1995, Yésou & Hirschfeld 1997, Panov & Monzikov 2000).

Thereafter, information on the phenotype of mongolicus remained scanty for a long time. Dement’ev (1951), in his review of the gulls of the USSR, simply stated that the plumage is similar to that of vegae and summarized Stegrnann’s (1934) description of the wing pattern. The most recent Russian systematic review (Stepanyan 1990) was even more anecdotal: ‘mantle colour a little darker than in cachinnans, leg colour varying from pink-grey to yellow’. In his review of the variation of the Palearctic large white-headed gulls, Devillers (1983) simply mentioned a mantle similar to or darker than that of Yellow-legged Gull L. michahellis, with more black on the primaries.

Then, western pioneers began to visit the breeding grounds of mongolicus, in particular Steve Madge. He described the iris as ’definitively’ dark (Madge 1983), before acknowledging that the iris in fact varies from almost white to very dark (Madge 1985). Also, he found the legs to be fleshy-pink in most adult birds (Madge 1985). Grant (1986) mentioned that birds seen in Mongolia were pink legged, some yellowish legged, and seemed to have a dark iris. Lastly, Pyzhianov & Tupitchyn (1992) published a short article, unfortunately hardly accessible to western gull students, that is the most detailed publication on the phenotypic variation of mongolicus to date. They mostly focused on leg colour which varied from pink to yellow and orange, none of these colours occurring in more than half of the adult birds at any of their study plots. Further articles on Asian gulls (eg, Kennerley et al 1995, Yésou & Hirschfeld 1997) were no more informative, with the exception of Panov & Monzikov (2000) who gave information on the wing-tip pattern of mongolicus.

FIGURE I Munsell’s index (37-step scale) of colour refraction of mantle colour for selected Palearctic taxa of Larus argentatus-cachinnans-fuscus complex. Darkness of grey mantle decreases from left to right. Only specimens of range given in type description, ie, lower reaches of Yenisei river in south-western Taimyr, have been included in Taimyr Gull L. (heuglini) taimyrensis. Specimens used for Birula Gull L. vegae birulai came from western Yakutia and east to Kolyma delta, those for Vega Gull L. vegae from east of Kolyma river to Chukchi peninsula. Argenteus, not representing a valid subspecies according to Dutch committee for avian systematics (CSNA) (Sangster et al 1999), refers to western and paler population of Herring Gull L. argentatus. Data from Barth (1966) and by courtesy of Andrey Filchagov (in litt) and Sergey Pyzhianov (in litt).

Results

Overall appearance

Mongolicus is a large and heavy gull, with a mean weight of 1140 g at the time of incubation (880- 1580 g, n = 11, unsexed). The wingspan, calculated from freshly dead birds (positioned as live birds), is 140-160 cm (with four females ranging from 138 to 146 cm and five males from 146 to 156 cm). Further measurements are given in table 1.
It is a large-chested, broad-necked and large-billed bird. The bulky appearance is partly tempered as the birds often stand rather upright on their long legs while the long wings give them an attenuated rear body.
The mantle is mid-grey, with MuseIl’s index of colour refraction ranging from 4.5 to 5.5 in 32 birds of Lake Baikal (Sergey Pyzhianov pers comm). This means that mongolicus is distinctly paler than heuglini, the mantle colour of many birds matching that of cachinnans as well as that of many vegae (including birulai) and taimyrensis (figure 1).

The wing-tip is among the darkest of the Asian taxa: usually seven (ranging from six to nine) outer primaries show black, sometimes extending onto the outermost coverts. There are two white mirrors, less often only one. Large white scapular and tertial crescents (13-27 and 19-42 mm wide, respectively, in 44 birds) are shown on the folded wing. The rest of the plumage is white, except for the pale grey underwing.

Mongolicus adult, July 16 2008, Lake Baikal, Mongolia (Arkady Zarubin). Adult birds in complete moult.	Mongolicus adult, June 2012, Khar Us Nuur, Mongolia (Andreas Buchheim). AL01-AL99. Wing-tag added in 2012.
Mongolicus adult, June 06 2012, Khar Us Nuur, Mongolia (Andreas Buchheim). AD62. Wing-tag added in 2006. Black on P4-P10. Note distinct white trailing edge to wing..	Mongolicus adult, June 06 2012, Khar Us Nuur, Mongolia (Andreas Buchheim). AD63. Wing-tag added in 2006. Complete moult started.
Mongolicus adult, June 2012, Khar Us Nuur, Mongolia (Andreas Buchheim). AJ23. Wing-tag added in 2012.	Mongolicus adult, June 2012, Khar Us Nuur, Mongolia (Andreas Buchheim). AL24. Wing-tag added in 2012.
Mongolicus adult, May 26-28 2012, Uvsijn Khar Us Nuur, Mongolia (Lutz von der Heyde). AL06. Wing-tag added in 2012. Red orbital ring, yellow iris, and red spot on gonys only on lower mandible. Black on 7 primaries. Medium mirror and full sub-terminal band on P10. Short pale tongue on P10. Small mirror on P9. Black spot on P4. P1 growing, P2-P3 missing, P4-P10 present, PMS=4.	Mongolicus adult, May 26-28 2012, Uvsijn Khar Us Nuur, Mongolia (Lutz von der Heyde). AL08. Wing-tag added in 2012. Bird with yellow legs. Note red orbital ring, yellow iris, and red spot on gonys extending just over the cutting edge on the upper mandible.

In contrast to the well-marked winter plumage of vegae and birds of Taimyr, mongolicus only shows poorly developed dark streaks on the head after the post-breeding moult (Dement’ev 1951). Birds still present at Lake Baikal in November show a virtually all-white head and neck (Sergey Pyzhianov pers comm).

The bill is yellow with a red gonydeal spot and shows variable dark markings. The iris varies from yellowish-white to dark grey-brown and the legs from pale flesh to bright orange. All these variations, and those in the wing-tip pattern, will be detailed in the next paragraphs.

Wing-tip pattern

According to a study of 89 adult-plumaged birds in the hand in colonies at Lake Baikal (an examination of museum skins did not result in additional information), at least some black occurs on the six (P5-P10) to nine outermost primaries (P2-P10), most often on the seven outermost ones (P4-P10), with a different number of black-tipped primaries in the two wings in c 10% of the birds (table 2). The black extends onto some or all outermost primary-coverts in 25 out of 84 birds with black on at least seven outer primaries. Such an extension of black onto the outer coverts (which otherwise always have a black shaft) was not observed in birds with only six black-tipped primaries. This could, however, be explained by the sample size. The proportion of adult birds with at least some black markings on the outer coverts is c 30%. Due to both the number of black-tipped primaries and the frequency of black on the coverts, the wing-tip of mongolicus is among the darkest of the Asian taxa of the argentatus-cachinnans-fuscus complex, averaging darker than in vegae. Only barabensis more frequently shows black on eight primaries (table 2).

Figure 8. Extent of black in the primaries of a sample of vegae and mongolicus. Source Surfbirds: IDENTIFICATION OF ADULT VEGA GULL: FIELD OBSERVATIONS FROM JAPAN, FEBRUARY 2003 by Chris Gibbins.

The tongue on the inner web of the outermost primary (P10) is pale grey. It is usually rather long, ending 9-15 cm from the primary-tip (see also Panov & Monzikov 2000) and covering about two-thirds of the width of the inner web. It is, however, shorter (ending up to 20 cm from the primary-tip) and narrower and somewhat darker in some birds, particularly those with eight or nine primaries with black, then resembling the usual vegae and birulai pattern. In such birds, the pale tongue can be less distinctly delineated from the black inner part of the web, being suffused with blackish.

White mirrors usually occur on both P9 and P10 but seven out of 67 (10%) adult-plumaged birds examined showed only a white mirror on p10. The white mirror on P10 invariably forms a complete band covering the full width of both webs. It is usually separated from the white wingtip by a subterminal black bar of 5-25 mm width although this bar was absent in two birds and incomplete in four others. The subterminal black bar was thus lacking, at least in part, in 9% of the handled birds. By way of comparison, this bar was incomplete or absent in 13 out of 45 (29%) skins of vegae and birulai, and it is usually absent in cachinnans (eg, Garner & Quinn 1997, Panov & Monzikov 2000). The length (measured along the feather-shaft) of the white mirror on P10 varied from 19 to 47 mm (with a mean of 36,4 mm), being 34-40 mm in half of the sample. It was worn at the tip and 48 and 55 mm long, respectively, in the two birds without a subterminal black bar. The white mirror on P9 extends onto both webs (68% of 60 birds with a white mirror on P9) or is limited to the inner web (32%), exceptionally to the outer web (one case was mentioned by Panov & Monzikov 2000, ie, 1% of 92 birds, pooling their and mine samples). It forms either a complete white band (nine birds, 15%) or more often one or two white spots of variable pattern: white on both webs, extending to the border of the inner web (28%); white on both webs, fully surrounded with black (25%); white on the inner web only, extending to the border of the web (12%); white on the inner web only, fully surrounded with black (20%). The maximum length of the white mirror on P9 (measured parallel to the feather-shaft) varied from 6 to 31 mm (with a mean of 17.7 mm), being 10-22 mm in 77% of the cases. No strong statistical relationship was found between the respective sizes of the white mirrors on P9 and P10 (n = 60).

Mongolicus adult, May 26-28 2012, Terchijn Tsagaan Nuur, Mongolia (Andreas Buchheim). AJ52. Uncommon pattern: white mirror merged with white tip, broken sub-terminal band. Long pale tongue on P10. Full band on P5. Black on outerweb of P4. No 'white moons', no white tongue tips on P6-P8. Moult score: P1 not visible, P2-P10 present.	Mongolicus sub-adult (5CY), May 24 2004, Khökh Nuur (Thomas Langenberg). AA63. Note black in alula. Full sub-terminal band on P10. Short pale tongue on P10, , leaving broad medial band (medial band much broader than length of mirror+tip). Full band on P4. Black on outerweb of P3. Thin 'white moons', white tongue tips on P6-P7. Moult score: P1-P10 present, PMS=0.
Mongolicus adult, May 26-28 2012, Oigon Nuur, Mongolia (Andreas Buchheim). AK15. Black on all 10 primaries, plus sharply demarcated black spots on centres of greater primary coverts. White tips on outermost primaries very small. Full sub-terminal band on P10. Short pale tongue on P10, leaving broad medial band. Full band on P4. Black on outerweb of P1-P3. No 'white moons', no white tongue tips on P6-P8. Moult score: P1-P10 present, PMS=0.	Mongolicus adult, May 29 2008, Lake Baikal (Thomas Langenberg). AG33. Large mirror on P10, small mirror on P9. Full sub-terminal band on P10. Medium pale tongue on P10, leaving broad medial band. Full band on P5. Black on outerweb of P4. The most common pattern.
Mongolicus adult, May 26-28 2012, Uvsijn Khar Us Nuur, Mongolia (Andreas Buchheim). AL10. Wing-tip pattern shown by a minority of birds: white mirror on P9 is missing. Much black on primaries, and small but sharply demarcated black spots on centres of greater primary coverts. Small mirror and full sub-terminal band on P10. Short pale tongue on P10. Almost full band on P4. Moult score: P1 missing, P2-P10 present, PMS=1.	Mongolicus adult, May 26-28 2013, Telmen Nuur, Mongolia (Andreas Buchheim). AL54. Common wing-tip pattern: mirror well separated from small white tip, by broad sub-terminal black band. Long pale tongue on P10, leaving narrow medial band (medial band about equal to length of mirror+tip). Mirror on both webs of P9. Full band on P5 and on P4. No 'white moons', no white tongue tips on P6-P8. Moult score: P1-P10 present, PMS=0.
Barabensis adult male, May 1998, Tengiz Lake, Kazachstan (Andreas Helbig). Limited amount of black in the outer wing, and both P9 and P10 show a clear delimited pale 'tongue' on the inner webs (which is commonly found in barabensis). Tiny mirror on P9 (77% of breeding birds at Lake Tengiz showed mirrors on both P9 and P10). Fig 16 from Phenotypic characterization, taxonomic rank and phylogenetic relationships of Armenian Gull Larus armenicus, by: Dorit Liebers & Andreas J. Helbig, in: Limicola 13-6, 1999.	Barabensis adult female, May 1998, Tengiz Lake, Kazachstan (Andreas Helbig). Mirror on P9 (77% in a small sample of breeding birds at Lake Tengiz, n = 22, showed mirrors on both P9 and P10). Fig 17 from Liebers & Helbig's work in 1999. It should be noted that Tengiz Lake in Kazachstan is home of barabensis in the view of Liebers & Helbig, but other authors (eg Panov and Monzikov) consider this place too far south, and expect influences (or even pure eastern) cachinnans. For barabensis the lakes and marshes of the Omsk region (like Chany Lakes) seem a better choice.

END OF PART 2

CONTINUE PART 3: BILL, EYE & LEG COLOUR IN MONGOLICUS

Larus cachinnans 2CY-3CY PUEX February 2011 & February 2012, France & Germany. Picture: Alain Fossé & Armin Deutsch.

From Ukraine.

Larus cachinnans 3CY PUHA February 2012, Varna, Bulgaria. Picture: Gabriel Martín.

From Ukraine.