Heuglin's Gull (L. heuglini / antelius)
Amir Ben Dov (Israel)
Chris Gibbins (Scotland)
Hannu Koskinen (Finland)
Mars Muusse (the Netherlands)
4cy / sub-adult heuglini: March
Characteristics and moult of "Baltic Lesser Black-backed Gull" Larus [fuscus] fuscus
THIS IS PART I (OF V)
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.
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.
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).
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).
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.
Materials and Definitions
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
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.
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
|Heuglini sub-adult March 04 2011, Eilat, Israel. Picture: Avi Meir.|
|Heuglini 4cy March 04 2011, Eilat, Israel. Picture: Amir Ben Dov.|
|Heuglini 4cy March 23 2012, Eilat, Israel. Picture: Amir Ben Dov.|
|Heuglini sub-adult March 09 2011, Ashdod, Israel. Picture: Amir Ben Dov.|
|Heuglini sub-adult March 02 2001, Bahrain: Ashkar harbour. Presumed male clearly show the general expression in heuglini.|