Heuglin's Gull (L. heuglini / antelius)

(last update: 6-3-2011)

4cy / sub-adult heuglini: March

Characteristics and moult of "Baltic Lesser Black-backed Gull" Larus [fuscus] fuscus
and “Heuglin’s Gull" L. [fuscus] heuglini

Visa Rauste

THIS IS PART I (OF V)

This is a translated abstract of the German paper published in Limicola volume 13 Issue 3 & Issue 4 1999. I translated the general parts and those dealing with heuglini, leaving out parts dealing with identification of nominate fuscus. I followed the original text as close as possible. Any misinterpretations due to translation are on my account. If you find any, or if you have suggestions, please let me know. Furthermore, I have added a few extra links to recent data, adding "MM" as editor. [M Muusse] When you read sentences in the text below, which include personal phrases, like "... my own observations ...", or "... I have observed birds in Archangelsk ...", this is copied from the original text and "I" is the author "Visa Rauste".

Introduction and Rational

Despite or because of the increased interest in identification of large gulls, there still remain several problems and unanswered questions. In this work, it's mainly about two gull species. One migrates regularly in numbers through Central Europe, but most records of that form in the western part are probably erroneously assigned to it; the other species has only few records, but probably it is overlooked.
Representatives of Lesser Black-backed Gull group (Larus fuscus in the broadest sense) breed in western and northern Europe in four different taxa: most western form graellsii breeds commonly from Portugal to Iceland and the Netherlands; from here there is a more or less broad gradual mixing zone into intermedius, which is found in Denmark, southern Norway and the Swedish west coast. From northern Norway and central Sweden eastwards we find fuscus; and from the Kola Peninsula heuglini. In the arctic part of Asia to the east three more, less investigated taxa, are found: taimyrensis, birulai and vegae (Glutz of Blotzheim & Bauer 1982).

The common feature shared by all four taxa are the upper part grey tones, which are slate gray (graellsii, heuglini and usually intermedius) to slate black (fuscus); in combination with normally yellow (pale-yellow – lemon to orange-yellow) legs in adult plumage, and a yellow bill with red spot on the gonys. Saturation in bare part colour is highly variable in all forms, as well as the extent of the red gonys-spot, which - in contrast to L. argentatus Herring Gull - often continues on the upper mandible. The orbital ring is normally deep red in breeding plumage; the iris is usually pale (white) yellow, but dark eyed individuals occur in heuglini more frequently than in the other forms. Based on the aforementioned basic features, adult birds in Europe are usually easy to assign the fuscus-complex, albeit that reliable assignment of individual birds within this group, especially in juvenile and immature plumage, still represents one of the most difficult problems of identifying birds in North and Central Europe.

In Central Europe, the question on the occurrence of the two north European forms fuscus and heuglini has gained interest due to better understanding of the plumage, an extensive colour marking project in Finnish Lesser Black-backed Gulls, and in combination with new and better knowledge of phenology in Central Europe. However, not all ideas have a solid base, and it is hoped that this work contribute to a further and better understanding of these taxa and will generate more and reliable data in the next years.

Many questions on systematics and taxonomy of this group and their relatives are still unclear; an annotated summary of the problems and an overview are provided by P.H. Barthel in Gruber (1995). Heuglini was occasionally seen as conspecific with the Herring Gull (e.g. in Grant 1986), but often categorized as a subspecies of L. fuscus (e.g. Glutz of Blotzheim & Bauer 1982, Cramp & Simmons 1983, Hario 1986); recently it frequently has been considered full species L. heuglini (e.g. Filchagov et all 1992, Harris et all 1996, Shirihai 1996) and this is supported by the German name “Tundramöwe” [Tundra Gull]. The proposal to separate the two westernmost forms (graellsii & intermedius) as separate species "L. graellsii" from L. fuscus, was recently described by the Taxonomic Commission of the Dutch Birding Association and accepted by the List of Dutch Avifauna (Sangster et al 1998). This new decision is only possible against a background of the phylogenetic species concept, which is controversial in both form and use, and therefore not a basis of taxonomic decisions in any other European country.

In the present study, no new positions are taken on the taxonomy of this group; here only “forms” or taxa of the super-species Larus [fuscus] instead of species or subspecies are used, without any prejudging aim of future taxonomic rearrangements. The plumage sequences and moult strategies of the poorly-known forms fuscus and heuglini are described and illustrated by images.
The determination of the two forms is discussed here mainly from the Finnish perspective and is based predominantly on own experiences of the author. Nevertheless, the outcomes will also be useful in other countries, especially in Central Europe, even though it is not possible to supply characteristics that will allow unambiguous determinations, always and under all circumstances, any time of the year.

Graellsii is widespread in western Europe and, in accordance, its plumage variability and moult sequences have been described quite well in the standard literature (Glutz of Blotzheim & Bauer 1982, Cramp & Simmons 1983, Grant 1986). The form intermedius received less attention, but it seems to appear very close to graellsii in some respects. Barth (1968, 1975) compared the variation in features of graellsii, intermedius and fuscus, but this was predominantly based on the upperparts grey tone of adult birds and only few body measurements. Recent findings on the primary moult of fuscus, which is significantly different from that of the two western forms, was first published by Jonsson (1998a).
The populations of the western forms have increased significantly over the past decades (Hagemeijer & Blair 1997). In contrast, fuscus faced a dramatic decline throughout the entire range, and the breeding success is very low in many areas (Hario 1994, Hario et all 1998). Nevertheless, fuscus is still common in large parts of Finland. The Finnish breeding population was estimated 19,000 pairs around 1960, but currently only about 7,000 pairs (Vaisanen et all 1998). The winter quarters are found mainly in the eastern Mediterranean and in East Africa and are reached by a predominantly southeastwards long migration routeover interior Europe.

Fuscus is a common migrant through eastern central Europe (Glutz of Blotzheim & Bauer 1982). However, west of a line through central Germany, it seems to be very rare (Glutz of Blotzheim & Bauer 1982, Muller 1996). There are observations of a few ringed birds in western Europe, be confusing Herring Gulls could not be excluded. Hence, from the Netherlands, ther is only unconfirmed evidence of its occurrence (van Hoogendoorn & Scheepers 1998, Winter 1999).

Heuglini is the least known of the four forms. Obviously due to the inaccessible breeding grounds of the tundra coast region in north Russian, east of 30°E, which still are difficult to
travel. Accordingly, available information is limited. Initial descriptions of the plumage development of heuglini can be found in Harris et all (1996), supplemented by additional information from Shirihai (1996), both merely based on observations from stop-over sites or winter quarters. However, these descriptions slightly contradict to my own findings. More recent information on the plumages of heuglini were given by Eskelin & Pursiainen (1998) and Beaman & Madge (1998). Published photos of certain heuglini from winter quarters or migration stop-over sites are scarce; and the right identification of photographed gulls is frequently questionable. The only published images of ​​juvenile heuglini known to me are two photos of flying birds from the breeding grounds, in Eskelin & Pursiainen (1998).

There is only little knowledge about the population size and development of heuglini. For several years we observe Lesser Black-backed Gulls “with pale upperparts” in Finland, but the identity so far is controversial due to the lack of clear defined criteria. Eskelin & Pursiainen (1998) have analysed these records (n = 312): due to the spatial and temporal phenology they concluded, that at least the majority of these birds should be labelled heuglini. Over the last years there is evidence of a significant increase (up to 1995 89 individuals; in 1996 64 birds; in 1997 159 birds, and since, a further increase) and this increase is probably not only due to a growing interest gull-watching. The western populations of heuglini are probably increasing, with subsequent area expansion (Filchagov et all 1992). Just like nominate fuscus, heuglini too is a long-stance migarnt, migrating over interior areas east of a line of Archangelsk, over Gorki, the Caspian Sea into the Gulf of Aqaba, in order to get to the main winter grounds of East Africa and the west coast of India.

Three old records from central Europe are published in Glutz of Blotzheim & Bauer (1982), including one from Germany (Helgoland 1888, labelled taimyrensis the eastern form). All old records are very hard to validate and may refer to other taxa as they were based on insufficient knowledge of characteristics. Nevertheless it can be expected that Siberian Gulls occasionally reach central Europe, especially with strongly increasing records in Finland.

Materials and Definitions

The present work is based predominantly on birds observed and photographed at Finnish landfills during the years 1997 to 1999. Additionally I have analyzed a large number of other photos from Finland, from the Middle East and Africa; and I examined museum specimen of especially immature fuscus and, when available, also heuglini-types (n = 3) in the collection of the Finnish Museum of Natural History in Helsinki.

Extremely valuable heuglini information could be collected by two trips to Archhangelsk, Russia (01.-04. Sept 1998 with Hannu Jannes; 09.-12. June 1999 with Antero Lindholm). Siberian Gulls could be studied here in comparison to hundreds of Herring Gulls.
In my material there is a bias to data from summer, so I will largely write about “summer plumage”. The age-classes are defined by the classification in calendar years (1CY: the bird is in its first calendar year, the year of birth; 2CY: the year following the year of birth, etc., up to 4CY [partly from 3CY when the plumage is usually indistinguishable from adults). This terminology seems to match best the moult strategy, which is very complex. Any further differentiation is probably not a good idea, as current knowledge is limited and large individual variation exsist in development of the taxa discussed here.

From now on, “fuscus“ will only be used for “Baltic Lesser Black-backed Gulls" Larus [f] fuscus. The term “fuscus-complex” comprises all Lesser Black-backed Gulls together (fuscus, graellsii, intermedius and heuglini). And “western forms” (or western Lesser Black-backed Gulls) are used for graellsii and intermedius. “Heuglini” or “Siberian Gull” refers here only to the form heuglini; and taimyrensis (or even eastern heuglini) is for the eastern neighbour which differs in some respects to heuglini. (The form taimyrensis is often paler at the upperparts and legs are often pink; these two features may be influenced by L. vegae which breeds further to the east.) Herring Gull normally means the widespread northeast European subspecies L. a. argentatus.

Occasionally I mention in the text colouring and patterns of primaries. To avoid comprehensive descriptions, the following abbreviations are used: the ten primaries are numbered descendantly consecutively: P1 is the innermost primary feather, P10, the outermost and these numbers corresponds to the order in which the primaries are renewed in an ordinary wing moult.

Table 1 shows the distribution of age-classes of studied birds of both Baltic Lesser Black-backed Gull and Siberian Gull. The numbers are not exact, because it often was not possible to exclude double observations. Fuscus in third and in subsequent calendar years, have been studied by hundreds.

Size and shape

Heuglini and fuscus. Compare grey tone and structure.

Structural features deserve fundamental importance in identification of large white-headed gulls, however there appears to be considerable individual variability in these characteristics and there are significant differences between the sexes. All descriptions of the structural characteristics in this study apply to average birds, although this is not always mentioned in the text. Some of these features can be used as diagnostic in ideal circumstances. Personal experience in the variability of familiar local species plays an important role for every observer, so these features are best applied to forms which are frequently encountered. Also, the risk of incorrect assignment of individual birds has then no statistical significance. Still, these structural features should not have equal importance as a possible scoring method for determination, when dealing with potential out-of-range birds.

Among European large white-headed gulls, Baltic Lesser Black-backed Gulls represent an extreme regarding the structural characteristics: it is the smallest and most slender taxon and has (relatively) long and narrow wings. Compared with Finnish Herring Gulls it is usually considerably smaller. Average body weight is only about two-thirds of an average Herring Gull (Hario 1996). But even though Finnish Herring Gulls are the biggest representatives of the entire argentatus-cachinnans-fuscus complex, there is still an overlap with fuscus. The overlap of different forms of lesser Black-backed Gulls is large in all measurements, hence size alone falls short as diagnostic feature. The wingtip projection in fuscus is usually conspicuously long (it is twice as long as the distance between the greater coverts and tertial tips, but this is not always apparent in juveniles (see Jonsson 1998a). The bill is slender, more obvious than in other large gulls and the gonys spot is ill-defined.

Siberian Gull size is between fuscus and Herring Gull and structurally it resembles Lesser Black-backed Gulls (here, here). The primary projection is somewhat shorter than in fuscus, but longer than in Herring Gull. Siberian Gull often leaves the impression of a large gull with a small head, a slender long neck and long legs (here). The shape of the bill is variable, sometimes as slender as in fuscus, but most vigorous (here). Many Siberian Gulls have a characteristic bill-shape: long, with fairly low base, but strong gonys, making the bill look front-heavy. The bill has a distinct curved tip, making the bill look bent at the tip.

Heuglini and graellsii. Compare structure.

When compared to heuglini, graellsii is less well-proportioned: “The head seems larger and squarish, the neck thicker and shorter, the wings shorter and broader and the legs thicker (Eskelin & Pursiainen 1998). Graellsii is also smaller and the bill shorter and relatively thicker. Unfortunately, there is no location to compare these two forms in the field together. The differences often seem to be useful (e.g. in photos), but one should agree with Eskelin & Pursiainen (1998), that “These differences however only apply to average birds and are hardly diagnostic for single individuals in the field".

The descriptions of the jizz of heuglini are surprisingly consistent. Kennerley e.g. (1995) described heuglini as to be similar to graellsii, but it differs in structure “in that it is less elegant, rather coarse”. Harris et all (1996) emphasized the large, vigorous jizz, the large head and large, strong bill in heuglini. The impression of birds I observed is different, maybe due to larger sized taxa that serve as comparison, and partly by the fact that Oriental heuglini are larger than western birds (Stegmann 1934). At least in my experience, heuglini appears usually more slender and long-winged, rather than particularly large or strong.

END OF PART I
CONTINUE AT PART II