Phenotypic variation and systematics
of Mongolian Gull
Pierre Yésou
In memory of Vladimir Vladimirovich Leonovich (1924-98)

S

ince Peter Grant’s pioneering work (cf Grant
1982, 1986), the knowledge of the identification and phenotypic variation of the gull taxa
belonging to the Larus argentatus-cachinnans-fuscus complex has dramatically increased inEurope. Initially, this progress benefited fromstudies conducted on breeding grounds wheremixed gull colonies allowed the comparison ofdifferent taxa (eg, Dubois & Yésou 1984). Then,the development of colour-ringing schemes gave
multiple opportunities to study the appearance ofbirds of known origin, sometimes at a great distance of the ringing site. Particularly remarkable
was the case of Pontic Gull L (cachinnans)cachinnans of which the field characters werefirst established from birds ringed in Black Sea
colonies and subsequently observed in Germany
during the winter season (Klein 1994, Gruber
1995). However, because only a small number ofbirds at the limit of the species’ winter range had
been studied, the phenotypic variation found was
not representative for the species. Therefore,
further studies of birds on the breeding grounds
were needed to describe in detail the phenotypicvariation of this taxon (Klein & Gruber 1997,
Liebers & Dierschke 1997).
The identification of the other taxa breeding in
the former USSR remains far less easy as mostdescriptions, based on birds seen on the breeding
grounds, are anecdotal (eg, Pleske 1928,
Dement’ev 1951) or even disputable. (Unfortunately, according to knowledgeable Russian ornithologists, the review by Judin & Firsova (1990) is
far from giving a reliable account of the argentatus-cachinnans-fuscus complex and will not be
considered here.) Also, although the skin collection in the Natural History Museum at Tring,
England, has been a reference for decades, it now
suffers from the doubtful validity of theMeinertzhagen collection (British Ornithologists’Union 1997) and the erroneous labelling of someskins (Lars Jonsson pers comm). The collections in
Russian museums harbour rich reference material
but have rarely been visited by western gull students. Moreover, very few western observers have[Dutch Birding 23: 65-82, 2001]

experience with the Asian taxa on their breeding
grounds (eg, Liebers & Dierschke 1997, Yésou &Hirschfeld 1997).
Further, the identification of the Asian taxa at
migration stopovers and on wintering grounds
still remains speculative in many cases. For
instance, birds looking as dark mantled as Lesser
Black-backed Gull L graellsii used to be identified
as Mongolian Gulls L (c) mongolicus in Hong
Kong (Kennerley 1987) but are now called Taimyr
Gulls L (heuglini) taimyrensis there as well as inJapan (Kennerley et al 1995, Hoogendoorn et al1996) although the only Asian taxon with such adark mantle is the western Siberian Heuglin’s
Gull L (h) heuglini (Yésou & Hirschfeld 1997).
Detailed descriptions based on birds studied on
the breeding grounds are available for only two
Asian taxa, ie, Armenian Gull L armenicus (eg,Buzun 1993, Filchagov 1993, Liebers & Helbig1999) and Baraba Gull L (c) barabensis (Panov &Monzikov 2000, who suggested that this taxon isa subspecies of heuglini), and are therefore stillneeded for the other Asian taxa.
In this article, the phenotypic variation of adultmongolicus is described and its systematic implications are discussed. It is mainly based on studies of birds in colonies at Lake Baikal, Siberia,
Russia, in the spring of 1992 (24 May-30 June)and of skins at the Moscow Zoological Museum,
the Zoological Institute of St Petersburg and thefield station of the University of Ulan Ude in the
Selenga delta, Lake Baikal. Moreover, I benefited
from the experience and guidance of Sergey
Pyzhianov who has been studying colonies ofmongolicus at Lake Baikal for years (and who has
developed an efficient trapping technique forringing mongolicus, by putting α-chloraline baits
at the nest), allowing me to visit all main colonies, except those in marshes at the north end of
the lake, and to handle more than 150 adultbirds.
Distribution and numbers
Mongolicus has a patchy breeding distribution,
ranging from south-eastern Altai to north-eastern
65Phenotypic variation and systematics of Mongolian Gull

85 Part of Bolshoye Toïnik, Maloye More, north-western Lake Baikal, Siberia, Russia, May 1992 (Pierre Yésou). This island holds
main colony of Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus (c 1000 pairs). Egg laying starts on c 5 May
when ice still covers large parts of Lake Baikal. Temperatures of below 0°C regularly occur at night up to mid-June. Water surface
temperature is still below 10°C by late June, except in some sheltered coastal bays 86 Mongolian Gulls / Mongoolse Meeuwen
Larus (cachinnans) mongolicus, Maloye More, north-western Lake Baikal, Siberia, Russia, June 1992 (Pierre Yésou)66

Phenotypic variation and systematics of Mongolian Gull
Mongolia and the western part of north-eastern
China (Dement’ev 1951). The isolated breeding
population of ‘Herring Gulls’ at Lake Khanka,
situated at the border of easternmost China andFar Eastern Russia, has also been claimed tobelong to this taxon (Pyzhjanov & Tupitsyn 1994)
but no systematic study of this population has
been published so far.
According to Pyzhjanov & Tupitsyn (1994) andPyzhianov (1996), only 750-1200 pairs are breeding in Altai, western Mongolia and Tuva (Tuvinskaya) Autonomous Region. There are c 3600 pairs
at Lake Khubsugul in northern Mongolia andc 7200 pairs at Lake Baikal. The lakes of Transbaikalya (Toresiskie Lakes) and north-eastern Mongolia and Hukun Nor in nearby China harbour
7500-10 000 pairs. The total population of mongolicus is estimated to be only 19 000-22 000
pairs (excluding the population of ‘Herring Gulls’at Lake Khanka), ie, less than 100 000 birds (including immature and non-breeding birds). Mongolicus is clearly a scarce gull.
Birds ringed at Lake Baikal have been recovered on the Pacific coast of Russia in autumn,
suggesting an eastward overland migration routeafter the breeding season (Sergey Pyzhianov perscomm). The entire population probably winters incoastal south-eastern Asia. Mongolicus has indeed been positively recorded in Hong Kong,Japan and South Korea (Kennerley et al 1995,
Hoogendoorn et al 1996, Lethaby et al 2000). It
has been claimed in Pakistan by Roberts (1991)
who relied only on bare-part coloration, a character of little or no diagnostic value in this case
(Yésou & Hirschfeld 1997). Therefore, the occurrence of mongolicus in western Asia remains
undocumented.
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), feetpink, 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 52-58. 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 areboth 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 andcloser to Birula Gull L v birulai, with black on theseven or eight outermost primaries and a subterminal black bar on p10 (primaries are numberedascendently). The latter taxon was given the namebirulai (Pleske 1928), in honour of the great sailorand Arctic explorer Birula, hence the male gender. Regrettably, many authors kept using thename ‘birulae’, a misspelling by Stegmann(1934). Birulai is hardly differentiated from vegae,
except for the variable leg colour and darker irisin some birds. It is treated as either a synonym ofvegae or a subspecies of it (eg, Stepanyan 1990,
Kennerley et al 1995, Yésou & Hirschfeld 1997,
Panov & Monzikov 2000).
Thereafter, information on the phenotype ofmongolicus 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 Stegmann’s(1934) description of the wing pattern. The mostrecent Russian systematic review (Stepanyan
1990) was even more anecdotal: ‘mantle colour alittle darker than in cachinnans, leg colour varying from pink-grey to yellow’. In his review of thevariation 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 thebreeding grounds of mongolicus, in particular
Steve Madge. He described the iris as ‘definitively’ dark (Madge 1983), before acknowledging thatthe iris in fact varies from almost white to very
dark (Madge 1985). Also, he found the legs to befleshy-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) publisheda short article, unfortunately hardly accessible towestern 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 andorange, none of these colours occurring in morethan 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 thewing-tip pattern of mongolicus.

67

Phenotypic variation and systematics of Mongolian Gull

87 Mongolian Gulls / Mongoolse Meeuwen Larus (cachinnans) mongolicus, Maloye More, north-western Lake
Baikal, Siberia, Russia, June 1992 (Pierre Yésou)88 Mongolian Gulls / Mongoolse Meeuwen Larus (cachinnans) mongolicus, Maloye More, north-western Lake
Baikal, Siberia, Russia, June 1992 (Pierre Yésou). Note that incidence of light influences perception of mantle colour

68Phenotypic variation and systematics of Mongolian Gullargenteus
cachinnans
mongolicus
vegae’birulai’rest of Taimyr
taimyrensis*(*type locality)

heuglinigraellsii
3

3,5

4

4,5

5

5,5

6

FIGURE 1 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 ofrange 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 andeast to Kolyma delta, those for Vega Gull L vegae from east of Kolyma river to Chukchi peninsula. Argenteus, notrepresenting 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 ofAndrey 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 (8801580 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
TABLE 1 Measurements (mm) of 42 adult (unsexed)
Mongolian Gulls Larus (cachinnans) mongolicus trapped at nests at Lake Baikal, Siberia, Russia, on 2-26
June 1992. Two different measurements of tarsus weretaken: 1 from centre of both joints as usually done onskins (‘museum’); and 2 from outer extremity of both
articulations which is most convenient way whenmeasuring live birds (‘field’)Range
Culmen48.0-61.7
Gonys height
16.6-22.0
Head plus bill length 115-139
Tarsus (museum)63.2-79.3
Tarsus (field)
67.8-87.8
Folded wing
432-494

Mean ± SD
54.9 ± 3.0
19.0 ± 1.4
126.3 ± 6.1
68.9 ± 3.2
80.5 ± 3.9
458.5 ± 14.8

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 largebilled bird. The bulky appearance is partly tempered as the birds often stand rather upright on
their long legs while the long wings give them anattenuated rear body.
The mantle is mid-grey, with Munsell’s index ofcolour refraction ranging from 4.5 to 5.5 in 32
birds of Lake Baikal (Sergey Pyzhianov perscomm). This means that mongolicus is distinctly
paler than heuglini, the mantle colour of many
birds matching that of cachinnans as well as thatof many vegae (including birulai) and taimyrensis(figure 1).
The wing-tip is among the darkest of the Asiantaxa: 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 scapularand 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 forthe pale grey underwing.
In contrast to the well-marked winter plumage
69Phenotypic variation and systematics of Mongolian Gull

89-91 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, Lake Baikal, Siberia, Russia,
June 1992 (Pierre Yésou). Note distinct white trailing edge to wing 92 Mongolian Gull / Mongoolse Meeuw Larus(cachinnans) mongolicus, adult, Lake Baikal, Siberia, Russia, June 1992 (Pierre Yésou). Note contrast between pale
grey coverts, darker grey band formed by bases of remiges and white (almost translucent) trailing edge to wingof vegae and birds of Taimyr, mongolicus onlyshows poorly developed dark streaks on the headafter 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 andshows variable dark markings. The iris varies fromyellowish-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 exam70

ination of museum skins did not result in additional information), at least some black occurs on
the six (p5-10) to nine outermost primaries (p210), most often on the seven outermost ones (p410), 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 alloutermost primary-coverts in 25 out of 84 birds
with black on at least seven outer primaries. Suchan 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Phenotypic variation and systematics of Mongolian Gull

93 Mongolian Gulls / Mongoolse Meeuwen Larus (cachinnans) mongolicus, adults, Lake Baikal, Siberia, Russia,
June 1992 (Pierre Yésou). Note contrast between pale grey underwing-coverts, darker grey band formed by bases ofremiges and white (almost translucent) trailing edge to wing 94 Mongolian Gulls / Mongoolse Meeuwen Larus(cachinnans) mongolicus, adults, Lake Baikal, Siberia, Russia, June 1992 (Pierre Yésou). Note distinct white trailingedge to wing71

Phenotypic variation and systematics of Mongolian Gull
TABLE 2 Number of black-tipped primaries in Mongolian Larus (cachinnans) mongolicus, Vega L vegae and Baraba

Gulls L (c) barabensis. Data on barabensis and vegae from Panov & Monzikov (2000) and from skins at Zoological
Institute of St Petersburg, Russia, respectively. a Number of black-tipped primaries can differ by one, thus bird
showing, for instance, eight black-tipped primaries in one wing and nine black-tipped primaries in other wing isscored 8.5. b Vegae includes Birula Gull L v birulai but no birds of Taimyr have been considered in sample.
c Panov & Monzikov (2000) did not look for asymmetry in number of black-tipped primaries. Also, their small
sample did not include any specimen with nine black-tipped primaries; however, such birds do occur (Yésou &Hirschfeld 1997)
mongolicus (%)

vegae b (%)

barabensis (%)

8.0
7.5 a
7.0
6.5 a
6.0
5.5 a
5.0

1
11
8
74
6
-

36
10
42
4
8

-c
39
39
22
-

Sample (n)

89

50

18

Number of black-tipped primaries
8.5 ablack-tipped primaries and the frequency of blackon the coverts, the wing-tip of mongolicus isamong 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).
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 theprimary-tip) and narrower and somewhat darker
in some birds, particularly those with eight ornine primaries with black, then resembling theusual vegae and birulai pattern. In such birds, thepale tongue can be less distinctly delineated fromthe black inner part of the web, being suffusedwith 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 acomplete band covering the full width of bothwebs. 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 andincomplete in four others. The subterminal black
bar was thus lacking, at least in part, in 9% of thehandled 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
72

varied from 19 to 47 mm (with a mean of 36.4mm), 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 bothwebs (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 acomplete white band (nine birds, 15%) or more
often one or two white spots of variable pattern:white on both webs, extending to the border ofthe 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 foundbetween the respective sizes of the white mirrors
on p9 and p10 (n = 60).
Bill colour
The bill is yellow, varying from pale yellow tobright orange-yellow, commonly with a paler tip.
The red gonydeal spot usually does not reach theupper edge of the lower mandible, falling shortby 2-3 mm. Dark markings (spots or broken lines
in front of the red gonydeal spot) occur in one outof three birds. Of 107 adult-plumaged birds trap-

Phenotypic variation and systematics of Mongolian Gull

95-96 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, upperwing, Lake Baikal, Siberia,
Russia, June 1992 (Pierre Yésou). Typical wing-tip patterns. Note large white mirror and subterminal black bar(white tip more or less abraded) on p10 and mirror of variable extent on p973

Phenotypic variation and systematics of Mongolian Gull

97 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, upperwing, Lake Baikal, Siberia,
Russia, June 1992 (Pierre Yésou). Less common wing-tip pattern. Note incomplete subterminal black bar on p10
98 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, (sub)adult, upperwing, Lake Baikal,
Siberia, Russia, June 1992 (Pierre Yésou). Wing-tip pattern shown by a minority of birds. White mirror on p9 is
missing. Note black markings on outer greater coverts in this otherwise fully adult-plumaged breeding bird74

Phenotypic variation and systematics of Mongolian Gull

99 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, (sub)adult, upperwing, Lake Baikal, Siberia, Russia, early
June 1992 (Pierre Yésou). This bird shows very dark wing-tip pattern, without white mirror on p9, and with many dark markings onouter coverts. Although bird was trapped at nest, its advanced moult stage (growing inner primaries and in particular fresh unmarked outer median coverts contrasting with older, brown-tinged, surrounding feathers) suggests that it has not yet reached fully
adult plumage 100 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, underwing, Lake Baikal, Siberia,
Russia, May 1992 (Pierre Yésou). Note contrast between mid-grey remiges, paler grey greater and median coverts, and white lesser
coverts. Shadow is partly masking pale grey tips to primaries that appear white and translucent when seen from below in flight75

Phenotypic variation and systematics of Mongolian Gull

FIGURE 2 Variability of iris pigmentation in Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus at

Lake Baikal, Siberia, Russia (redrawn from field sketches of birds in hand) (Pierre Yésou)ped at nests and examined in the hand, 17%
showed dark markings on the upper mandible
only and 15% on both mandibles (in one extreme
case, the markings formed an almost complete
dark bill band of c 3 mm width).
Eye colour
The orbital ring was vermilion-red in all adultplumaged birds I examined in the hand.
Pyzhianov & Tupitchyn (1992) described the irisas ranging from pale ashy-grey to olive-grey todark smoky-grey. 54 and 68% of their samples of
Lake Baikal and Lake Khubsugul, respectively,
were pale eyed. They found no correlation between iris and leg colours (a point I did not check).
In the birds I examined in the hand, the iris wasdull yellow (very pale, almost whitish, in some),
usually peppered with grey (pale bluish-grey todark grey-brown) minute spots in variable density
over a much variable extent of the iris surface. In
some birds, the grey was peppered quite uniformly over the iris, often with a few small aggregations forming dark marks on the overall pale eye.
In other cases, dense grey spots formed one ormore large dark areas over the eye while sparse
spotting left the yellow iris colour showing over
the rest of it (figure 2). Eye darkness is not sex
related. Pale eyes and dark eyes are found in bothmales and females and pairing occurs irrespectiveof the iris colour (of eight pairs, the male had
darker eyes than the female in four cases and thefemale had darker eyes than the male in threecases; the partners of the remaining pair showedsimilarly coloured eyes).
76

Such a high variability of iris pigmentation
makes it difficult to accurately comment on theeye colour of mongolicus. In a first analysis of 43
birds in the hand, I classified 28% of them as pale
eyed, 42% as intermediate and 30% as dark
eyed. A more detailed analysis, including two
more samples (table 3), showed that nearly onethird was pale eyed while grey spots covered
more than half of the iris surface in another third.
Really dark-eyed birds, however, accounted forless than 10%.
In the field, colour assessment is less easy. Of
236 adult birds studied through binoculars ortelescope, 89% were classified as yellow or
yellowish eyed. It thus seems that eyes classified
as pale grey in the hand are perceived as yellowish in the field while dark-eyed birds accounted
for only 4% in the field sample (not statisticallydifferent from the 8% found during the in-handexamination).
Leg colour
Pyzhianov & Tupitchyn (1992) described the highdegree of variability of the leg colour at Lake
Baikal and in Mongolia. They examined various
series of birds in the hand, comparing the leg
colour with colour charts. Grey legs accounted
for 22-40%, yellow 13-27%, pink 21-46% andflesh 4-10%, while 6-30% of the birds showed
mix-coloured legs. The proportion of each colour
type varied between colonies and from one year
to the other in a given colony. Also, in a proportion of birds, the leg colour showed temporalchanges. According to Pyzhjanov (1998), notPhenotypic variation and systematics of Mongolian Gull
TABLE 3 In-hand assessment of dominant iris colour in three samples of adult Mongolian Gulls Larus (cachinnans)mongolicus trapped at nests at Lake Baikal, Siberia, Russia, in May-June 1992 (percentage of sample size).
a Several colonies. b Different colony
Maloye More a
31 May-7 June (%)

Maloye More b
15 June (%)

North-eastern Lake Baikal
26 June (%)

Pooled (%)

Yellow (grey < 10%)
Yellowish (grey 10-50%)
Pale grey (grey > 50%)
Dark grey
Brown

28
44
21
5
1

28
42
21
9
-

42
8
33
17

29
41
22
6
2

Sample (n)

97

43

12

152

only the intensity but also the tone of the coloration changes. He hypothesized that these changes
are related to external conditions (food composition) and age. It is a largely acknowledged factthat carotine-rich food can enhance the expression of the carotinoid colouring matter in the legsof gulls (cf Lönnberg 1933). Any relation withage, however, remains to be proven.
I examined in the hand the legs and feet of 152
birds of most colonies I visited at Lake Baikal. It
readily appeared that the fleshy-pink colour
usually was tinged with some yellow pigment
over a very variable extent. Yellow was more
often found on and around the knee and on therear leg while webs often were of a deeper pink(one pink-legged bird with orange webs was mostunusual). Some birds exhibited either bright pinkor yellow (pale to bright, then resembling michahellis) legs but most showed a variable leg colour.
This rendered any reference to colour chartsrather subjective and I relied on my own assessment when establishing the dominant leg colourin the examined adult birds. Of them, 15.8% had
flesh-to-pink legs, 76.3% yellowish-flesh, 5.9%
pale yellow and 2% bright yellow.
In the field, the perception of the yellow tinge
varies markedly, depending on the light incidence
and on whether the legs are wet or not (yellow
shows better on wet legs). Even birds which seemto have yellow legs when looked at them with the
naked eye occasionally showed pinkish legs
through binoculars. The field score neverthelessmatched the in-hand results, with almost all 555
birds studied in the field showing ‘pale’ (ie, flesh
or pink more or less obviously admixed with yellow) legs and only seven (1.3%) yellow legs.
Discussion
Mantle colour and wing-tip pattern
On the basis of the type specimen collected innorth-western Mongolia, Sushkin (1925) describ-

ed the mantle of mongolicus as being darker thanthat of cachinnans, a statement repeated by Stepanyan (1990). Dement’ev (1951) described the
mantle colour of mongolicus as similar to that ofvegae. My research on museum skins showedthat some birds of north-western Mongolia are on
the darker side of the variation found in mongolicus, a tentative explanation of Sushkin’s description. Many mongolicus, however, are paler than
this and their mantle colour overlaps with that ofboth cachinnans and vegae (see figure 1). Birds ofthe latter taxon can, however, be paler than any
mongolicus, particularly in the northernmost partof the range of birulai (unpublished data frommuseum study).
The grey inner tongue on p10 was mentioned
by Sushkin (1925) but no information was available on the wing-tip pattern of mongolicus, except
for Stegmann’s (1934) statement of seven to eight
primaries with black and the presence of a subterminal black bar on p10, and complementary
figures given by Panov & Monzikov (2000). My
reference to a much larger set of birds showed thatthe inner tongue on p10, although usually pale
grey (ie, paler than in vegae, which is in agreement with Sushkin’s original description), is darker
in some birds and then resembles the patternfound in vegae and birulai. Also, the number ofprimaries with black (six to nine) is more variable
than previously thought and the presence of a
subterminal black bar on p10 is no absolute rule.
Obviously, the larger the number of birds studied, the better the understanding of the phenotypic variation. Our knowledge, first based on
small samples (either museum series or migrants
of known origin), has strongly increased by studying birds in colonies (see, for instance, Buzun
1993, Filchagov 1993, Liebers & Dierschke 1997,
Liebers & Helbig 1999, Panov & Monzikov
2000). This also holds for measurements, therange of which often increases with sample size
(mean values are less affected).
77Phenotypic variation and systematics of Mongolian Gull

101 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, Lake Baikal, Siberia, Russia, June
1992 (Pierre Yésou). Dark-eyed bird. Note that red gonydeal spot does not reach upper edge of lower mandible
102 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, Lake Baikal, Siberia, Russia, June
1992 (Pierre Yésou). Dark-eyed bird. Note that red gonydeal spot does not reach upper edge of lower mandible.
Note also dark bill-marking
103 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, Lake Baikal, Siberia, Russia, June
1992 (Pierre Yésou). Pale-eyed bird. Note that red gonydeal spot reaches upper edge of lower mandible. Such an
extension of red is only found in a minority of birds. Note also small dark mark on upper mandible
104 Mongolian Gull / Mongoolse Meeuw Larus (cachinnans) mongolicus, adult, Lake Baikal, Siberia, Russia, June
1992 (Pierre Yésou). Pale-eyed bird

Bare-part coloration
The bare-part coloration of mongolicus I
established agrees with most previous descriptions in the literature. The vermilion-red orbitalring was mentioned in Sushkin’s (1925) originaldescription. The variability of iris and leg colours
is known since Madge (1985). It remained, however, unquantified until Pyzhianov & Tupitchyn(1992) and this study.
Such a large variation in bare-part coloration in
one population may be surprising to western78

birders accustomed to colonies inhabited by uniformly looking Herring L argentatus, Yellowlegged or Lesser Black-backed Gulls. However,the fact is that highly variable grey or brown pigmentation over the yellow iris occurs in breeding
birds of all Asian taxa of the argentatus-cachinnans-fuscus complex, seemingly being the least
marked in vegae (Filchagov 1993, Liebers &Dierschke 1997, Liebers & Helbig 1999, Panov &Monzikov 2000, Andrey Filchagov and V I Grabovsky pers comm, pers obs). It also occurs,Phenotypic variation and systematics of Mongolian Gull
although very rarely leading to grey-looking
irides, in michahellis (N Baccetti pers comm).
Regarding the variability of leg colour, this is also
found in cachinnans (Liebers & Dierschke 1997,
V I Grabovsky pers comm) and is commonplacein northern Siberia, from north-western Taimyr to
the Lena delta at least, over the range of birulai(eg, Yésou & Hirschfeld 1997).
Until Hirschfeld (1992) and Madge (1992),
little attention has been paid to the frequency andsize of dark bill-markings in adult large gulls. Thisis the first time that these are described for mongolicus. Such bill-markings are shared, in variable
size and proportion, with the Asian taxa of theargentatus-cachinnans-fuscus complex (Filchagov
1993, Liebers & Dierschke 1997, Yésou &Hirschfeld 1997, Panov & Monzikov 2000).
Systematics
Recently proposed systematic arrangements (eg,Devillers & Potvliege 1981, Haffer 1982, Devillers 1983, Stepanyan 1990, del Hoyo et al 1996,
Sangster et al 1999) have generally presentedmongolicus as a subspecies of cachinnans, inclassifications encompassing (almost) all thesouthern taxa of Palearctic yellow-legged large
white-headed gulls under cachinnans. This treatment is based on the supposed continuity in distribution (as given in oversimplified distribution
maps like, for instance, the one in Yésou &Hirschfeld 1997), similarity in mantle colour andpossibly also in the white head in winter shownby most southern taxa (atlantis, a subspecies ofcachinnans according to some of the abovementioned authors, is dark hooded in winter).
This, however, remains a hypothetical classification, pending further research on the relationships
between cachinnans and neighbouring taxa (eg,Yésou et al 1994, Sangster et al 1999).
On the basis of the now available information,
it is clear that there are marked phenotypic differences between mongolicus and cachinnans,particularly in wing-tip pattern (the number of primaries with black, the grey inner tongue and subterminal black bar on p10; see, for instance,
Garner & Quinn (1997) and Jonsson (1998) for a
description of the wing-tip of cachinnans) andunderwing colour (pale grey in mongolicus andwhite in cachinnans). Such differences are sufficient to consider mongolicus and cachinnans as
different species under the Phylogenetic Species
Concept (PSC). Proponents of the BiologicalSpecies Concept (BSC) could argue that intergradation remains a possibility in a still undocumented contact area. If intergradation ever occurs, it

should in any case be limited by the low densityof both mongolicus and cachinnans in theneighbouring part of their respective breeding
ranges (Pyzhjanov & Tupitsyn 1994, Pyzhianov
1996, Andrey Filchagov pers comm). Occasional
mix-pairing has no taxonomic value, even underthe BSC (see, for instance, the occasional argentatus x graellsii or argentatus/graellsii x michahellis
pairs in western Europe; Yésou 1991). Furthermore, a preliminary mitochondrial DNA analysis(Crochet 1998) showed that mongolicus largely
differs genetically from cachinnans, thus invalidating the hypothesis of the existence of significant gene flow between the two taxa. In fact,mongolicus is genetically closer to the Siberiantaxa heuglini and in particular birulai of Taimyr(Crochet 1998, who had no access to material ofeastern birulai and vegae).
Also, although no comparative analysis has
been performed to elucidate vocal relationships
in Siberian gulls, the vocalizations of mongolicus
clearly differ from those of cachinnans (according
to observers with a hearing ability better thanmine) and seem closer to those heard in Taimyr(Andrey Filchagov pers comm).
Should mongolicus be considered as a full species or should it be considered as a subspecies ofvegae, together with birulai? The fact is that thesetaxa resemble each other although differences
have been noted, particularly in wing-tip pattern(the number of primaries with black, the size andcolour of the tongue on p10, proportion of birds
without a complete subterminal black bar onp10) and in winter-plumage markings.
The ranges of vegae (including birulai) andmongolicus, which breed in the Arctic tundra andat lakes in the steppe belt, respectively, areseparated by a more than 1000-km wide taiga
belt where no large gulls are known to breed. The
breeding environment of mongolicus and vegae
nevertheless shows marked similarities, due to thelate and cold spring at Lake Baikal. As an illustration of this, the behavioural adaptation to lowtemperatures shown by fleas parasiting nests ofmongolicus at Lake Baikal is otherwise known
only from fleas of Arctic and Antarctic seabirds(Guiguen et al 1993). Could then some spring
migrants, which regularly stop over at Lake Baikal
when en route to Taimyr and possibly western
Yakutia (Sergey Pyzhianov pers comm), be attracted by seemingly favourable environmental conditions and stay to breed at Lake Baikal, thenleading to some degree of intergradation? This
seems, however, unlikely as Arctic birds start tobreed 35-45 days later than Lake Baikal birds
79Phenotypic variation and systematics of Mongolian Gull
(Filchagov et al 1992, pers obs) and they are presumably hormonally not in breeding condition
when passing through the Lake Baikal area.
In conclusion, species status should be given tomongolicus under both the PSC (diagnostic differences in, for instance, wing-tip pattern and winter-plumage markings) and the BSC (not interbreeding freely to any significant degree). It thenappears that the Asian taxa until recently
considered as subspecies of cachinnans are now
better taken as full species, namely armenicus,
barabensis and mongolicus (Buzun 1993, Filchagov 1993, Liebers & Helbig 1999, Panov & Monzikov 2000, this study), as Panov & Monzikov’s(2000) suggestion that barabensis is a subspeciesof heuglini is easily rejected on arguments similar
to those I have developed about the relationships
between mongolicus and other taxa.
Acknowledgements
Vladimir Vladimirovich Leonovich (1924-98), afriend of the arts, was the acknowledged curatorof important art collections in Moscow. He also
was a much-respected amateur ornithologist andone of the best oologists in Europe. I have been
graced with his company from Moscow to Lake
Baikal and during my stay there, benefiting fromhis intellectual and human richness. This article isdedicated to his memory.
My field and museum work in Russia was partof a co-operation scheme between the Russian
Academy of Sciences and my employing structure(ONC-Faune Sauvage, French Ministry of Environment), and my visit to Lake Baikal was arranged in the framework of ornithological expeditions
then organized in Siberia by Academician
Professor E E Syroechkovsky from the Severtsov
Institute in Moscow. I have been friendly welcomed and looked after all around Lake Baikal by
Sergey Pyzhianov – who willingly shared his
wide knowledge of the birds, the lake and its
environment – and his wife Olga. I am muchindebted to them. Also, the biologists fromvarious scientific institutions in Irkutsk and Ulan
Ude have always welcomed me to their field stations; their company has been appreciated bothat work and after it. Thanks to their curator Pavel
Tomkovich, I had access to the skin collection in
the Moscow Zoological Museum where I benefited from the expert guidance of Andrey Filchagov
who also showed me his skin collection andshared long conversations on the systematics andbiology of Holarctic large white-headed gulls.
Under the recommendation of V M Loskot, curator at the Zoological Institute of St Petersburg,
80

L V Firsova kindly prepared for me a part of theimpressive skin collection held there. The company of Elena Zubakina, the wife of the reputed
ornithologist Victor Zubakin, an expert gull student himself, has been most pleasing and helpful
during my return trip from Lake Baikal to St
Petersburg and Moscow. Sergey Pyzhianov,Andrey Filchagov and E I Kozhurina have greatly
helped with the translation of Russian articles.
Lastly, Gerald Oreel invited me to write thisarticle for Dutch Birding after the presentation I
gave on the same topic at the 4th International
Gull Meeting (organized by Ted Hoogendoorn,
Dirk Raes and Pascal Raevel) at Le Portel, Pas-deCalais, France, on 7-10 October 1999. Many
thanks to all of them.
Samenvatting
FENOTYPISCHE VARIATIE EN SYSTEMATIEK VAN MONGOOLSE
MEEUW Mongoolse Meeuw Larus (cachinnans) mongolicus broedt van Zuidoost-Altai naar Hukun Nor in
Noordoost-China, over Noord-Mongolië, het Tuva
Autonome Gebied, het Baikalmeer en Transbaikalia.
(De taxonomische verwantschap van de Zilvermeeuwen van het Khankameer (gelegen in het grensgebied van Oost-China en het Russische Verre Oosten) is
onbekend.) De gehele populatie, geschat op slechts
19 000-22 000 paren (met inbegrip van 7200 paren in
het Baikalmeer) of minder dan 100 000 vogels (metinbegrip van jonge en niet-broedende exemplaren),overwintert waarschijnlijk in de kustgebieden van
Zuidoost-Azië.
In het voorjaar van 1992 onderzocht de auteur defenotypische variatie van broedende mongolicus in het
Baikalmeer. Dit onderzoek had onder meer betrekking
op meer dan 150 op of bij nesten gevangen vogels.
Mongolicus is een grote en zware meeuw, met een
gemiddeld gewicht van 880-1580 g tijdens de broedtijd; de vleugelspanwijdte bedraagt 140-160 cm. Hij
heeft een middengrijze (‘mid-grey’) mantel (de Munsell
index, een maat voor de refractie van kleuren, varieert
van 4.5 tot 5.5). Dit betekent dat mongolicus een duidelijk lichtere mantel heeft dan Heuglins Meeuw L (heuglini) heuglini. Hierin komen vele mongolicus overeen
met vele Vegameeuwen L vegae (met inbegrip van
Birulameeuw L v birulai) en Taimyrmeeuwen L (h) taimyrensis. Mongolicus heeft in vergelijking met andereAziatische taxa een van de donkerste vleugelpunten.
Zwart bevindt zich gewoonlijk op de zes tot negen buitenste handpennen, het vaakst op de zeven buitenste
handpennen). Het zwart komt soms voor tot op de buitenste handdekveren. Gewoonlijk komt een witte spiegel (handpenvlek) voor op de buitenste twee handpennen (p9 en p10), minder vaak alleen op de buitenste
handpen (p10). Meestal scheidt een subterminale zwarte band de witte spiegel van de witte handpenpunt. In
tegenstelling tot Arctische meeuwen vertoont mongolicus slechts een zwakke kopstreping na de rui naar adultwinterkleed. De gele snavel, met een rode gonysvlek,

Phenotypic variation and systematics of Mongolian Gull
vertoont een variabele zwarte tekening. De iriskleur
varieert van geelachtig wit tot donker grijsbruin en depootkleur van licht vleeskleurig tot helder oranje.
Mongolicus vertoont duidelijke fenotypische verschillen met Pontische Meeuw L (c) cachinnans. De
belangrijkste verschillen worden gevormd door de tekening van de vleugelpunt (het aantal handpennen met
zwart, de grijze tong en subterminale zwarte band opp10) en de kleur van de ondervleugel (licht grijs bij
mongolicus en wit bij cachinnans). Er bestaan ook duidelijke vocale en genetische verschillen tussen deze
twee taxa. Mongolicus lijkt nauwer verwant met vegae(met inbegrip van birulai) en taimyrensis alhoewel hij
van deze taxa verschilt door de tekening van de vleugelpunt en het winterkleed. Doortrekkende vegae entaimyrensis verblijven in het voorjaar op het Baikalmeer. Hybridisatie van deze Arctische meeuwen met
lokale mongolicus lijkt onwaarschijnlijk aangezien dezemeeuwen in broedbiologisch opzicht 35-45 dagen‘achterlopen’. De fenotypische, vocale en genetische
verschillen van mongolicus met cachinnans en het feit
dat mongolicus reproductief geïsoleerd lijkt te zijn vande verwante Arctische taxa vegae (met inbegrip vanbirulai) en taimyrensis vormen aanwijzigingen dat mongolicus als een aparte soort dient te worden opgevat(zowel onder het Fylogenetisch als het BiologischSoortconcept).

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Madeiran Storm-petrel off Denia,
south-eastern Spain, in June 1997
On 30 June 1997 at 16:00, I noticed an unfamiliar storm-petrel Oceanodroma close to theshore near the harbour of Denia, Alicante, Spain.
It was feeding amongst c 50 European Stormpetrels Hydrobates pelagicus and was quite easily picked out by its larger size and foraging behaviour. I could observe the bird for 4-5 minwith binoculars and telescope at a distance ranging from 100 to 125 m, and I identified it as a
Madeiran Storm-petrel O castro (cf Lewington etal 1991, Jonsson 1992).
At first sight, the bird looked like a dark Leach’s
Storm-petrel O leucorhoa, about equal in size,
but with a very large white rump patch which
extended onto the flanks and undertail-coverts, as
in European Storm-petrel. Upon closer look, thetail was only slightly forked, unlike Leach’s, andthe wingbar on the upperwing was hard to see ata distance of c 125 m. The flight was completely
different from either European or Leach’s: a directflight, with the wings held backwards like a small

skua Stercorarius. It flew in a line parallel to thecoast, first from north to south, then it turned aftera few 100 m to do it in reverse direction. This
feeding flight was repeated at least five times.
In this area, European Storm-petrel breeds on
the nearby Balearic isles of Ibiza and Formentera
and in the coastal region south of Denia (eg,Islote de Benidorm and Tabarca) (Purroy 1997),
and flocks of 30-50 birds were seen daily, feeding close to the pier at Denia from June to August
1997.
This observation has been accepted by the
Spanish rarities committee (Eduardo de Juana inlitt) and constitutes the third record of Madeiran
Storm-petrel for Spain and about the 10th forEurope, and it is the first for the Mediterranean.
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Tobi Koppejan, Segeersweg 38, 4337 LD Middelburg, Netherlands (gelatik@zeelandnet.nl)
82[Dutch Birding 23: 82, 2001]