Ardea
Official journal of the Netherlands Ornithologists' Union

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Voous K.H. (1961) Micro-geographical variation in Netherlands Herring-Gulls, Larus argentatus. ARDEA 49 (1-2): 69-72
1. From February 4th till March 14th, 1960, an adult gull of the Larus fuscus-argentatus-cachinnans group was observed in Scheveningen. It was characterized by a very heavy build, yellow legs, slate grey mantle (darker than that of a Kittiwake), long wings reaching far beyond the tail and marked with much black on the tips, red eye-ring and pure white, unspotted head and neck. The black of the wing-tips spread out over the 7 outer primaries, very probably also over the eighth; the tip of the outer primary was pure white, that of the second having only a white 'mirror' on the inner web. For the determination of this gull the study of much literature proved necessary. In doing so the writer came to realize the 'Babylonic' confusion existing among writers who dealt with the species group in question. The writer being no systematist himself has been forced to use his common sense in search of a solution. 2. The 20 forms described in the species-group can be geographically divided into 4 groups: 1. the North American group: californicus, smithsonianus, thayeri, kumlieni and glaucoides; 2. the North Siberian group: antelius, taimyrensis, birulai and vegae; 3. the South Palaearctic group: atlantis, michahellis, ponticus, cachinnans and mongolicus; 4. the North West European group: argenteus, argentatus, graellsii, intermedius, juscus and omissus. After having given the characteristics of the 20 forms the writer concludes that for the determination neither the North American nor the North West European group need be considered. Of the North Siberian group only antelius and taimyrensis may be considered, birulai being too light and vegae having flesh-coloured legs and a heavily spotted 'winter head'. Among the South Palaearctic group only atlantis and the almost equally dark populations of michahellis along the Portuguese coast may come into consideration, all other forms being too light. 3. On the basis of the investigations of Stegmann (1934), Meinertzhagen (1935), Voous (1946) and Stresemann & Timofeeff-Ressovsky (1947) a gradation scale is drawn up in which the 20 forms are arranged according to the relative lightness (darkness) of their mantle. The Scheveningen gull (which was darker than a Kittiwake but lighter than a British Lesser Black-backed Gull) in this scale would belong to the form antelius, more especially to the larger and lighter Siberian populations thereof. It is further shown that all other field marks of the bird also correspond exactly with antelius. The writer rejects the point of view of Meinertzhagen (1950, 1954) who considers antelius to be a synonym of heuglini Bree. Neumann (1934) has shown that Bree's type and co type (which Meinertzhagen did not inspect) exactly match the birds of the Taimyr Peninsula and the Gulf of Jenissei. Therefore, taimyrensis - and not antelius - should be considered a synonym of heuglini, if it would be necessary or convenient to distinguish two different forms in North West Siberia and North Russia. 4. For the writer the next step is to find the exact species name of antelius. To this end he reviews the different accepted opinions of Hartert (1921), Dwight (1925), Stegmann (1934), Peters (1934), Meinertzhagen (1935), Steinbacher (1938), Geyr von Schweppenburg (1938), Mayaud (1940), Stresemann & Timofeeff-Ressovsky (1947), Fisher & Lockley (1954), Alexander (1954), Johansen (1958) and Voous (1959, 1960), The writer is inclined to question the value of a system of scientific nomenclature which would justify the systematic classification of this Scheveningen antelius-bird in 12 different ways! For a good understanding of the species-group the writer considers it of importance to solve the 'riddle of omissus'. Pleske (1928) remarked that Sushkin and his assistant Stegmann had discovered that the gulls of the Gulf of Finland, the White Sea and the Murman Coast belong to a form differing from the typical form Larus argentatus Pontoppidan in having 'larger dimensions, darker mantle and the white pattern of the first primary differing in shape; the legs of this subspecies are sometimes flesh-coloured, sometimes yellow'. Pleske called this form Larus argentatus omissus Sushkin, which was obviously a premature statement as Sushkin never got the length of describing this form. Moreover it soon too became apparent that the views Pleske ascribed to Sushkin were, not exact. The gulls Pleske had in mind are no darker than those of North Scandinavia and the Baltic Sea. Stegmann who continued the work of Sushkin does not even mention omissus! One thing and another has nevertheless led to the use of the names argentatus and omissus to describe populations of different content. Witherby and Dementiev, who do not recognize the North Sea form argenteus, identify this form with argentatus and group the pink-legged Scandinavian argentatus and the yellow-legged omissus together under the name omissus. On the contrary, Stegmann who does recognize argenteus as a distinct subspecies gives the name of argentatus to the bimorph-legged gulls which Witherby, and Dementiev name omissus. Lastly, there is the point of view of Stresemann and Voipio who recognize both the pink legged forms argenteus and argentatus as well as the yellow-legged omissus. This last point of view is adopted in this paper in order to frame as accurately as possible the question: what is omissus, a yellow-legged 'variation' of the pink-legged Herring Gull (of American origin) or an independent geographical form of Eurasian origin? To this question Voipio (1954) has given the answer. He has shown that the yellow-legged gulls that have since about 1920 been populating Finland and the Baltic countries in ever increasing numbers cannot be distinguished taxonomically from the South Asiatic form cachinnans (incl. ponticus). Voipio connects these findings with the theory that this recent colonisation by cachinnans has to do with the drying up of the Aralo-caspian area. Possibly in the time of the climatologically optimum ( 6000 B.C.) just such an exodus of cachinnans must have taken place which according to Voipio would account for the yellow-legged populations of the White Sea and of the interior of the Kola Peninsula. It is to the credit of Voipio that he has proven the incorrectness of the conclusions of Witherby, Stegemann and Dementiev who were not aware of the vast difference between the American 'red race' (the pink-legged argentatus) and the Asiatic 'yellow race' (the yellow-legged omissus = cachinnans). 5. Accepting the views of Geyr, Stresemann, Voipio and Voous regarding the evolutional history of the species-group the writer assumes that in pleistocene times two groups of refugal populations have developed, divided and isolated from each other by the East Siberian ice barrier. The pink-legged gulls (argentatus) lived east of this barrier and the yellow-legged gulls (cachinnans) on the west side in the Aralo-caspian area. The ancestors of argentatus dispersed in interglacial times over the American continent which led to the gradual development of the forms of the North American group. Post glacially an emigration of smithsonianus to West Europe must have taken place (argenteus, argentatus). The ancestors of cachinnans spread in interglacial times over the Eurasian continent which resulted in the development of heuglini (taimyrensis) and antelius in the north, michahellis and atlantis in the west, and - in relatively recent times - of 'omissus' in the northwest. The writer agrees with Stresemann and Voipio that graellsii and fuscus originated from atlantis and not from antelius. Post glacially the ancestors of argentatus also spread over North East Siberia (vegae and birulai). In their westward drive the populations of birulai met the yellow-legged heuglini moving to the east which apparently led to hybridization on a rather large scale. In the same way the yellow-legged mongolicus dispersing to the east intermingled with a hot yet identified pink-legged form inhabiting the East Asian coast. These facts would explain why the N.B. Siberian and S.B. Asian gulls are bimorph with regard to the colour of their legs. 6. As a hypothetical result of this evolutional history the following present facts can be established: 1. that the whole Siberian and South Palaearctic group are connected by zones of intergradations and therefore belong to one species; 2. that no contact exists on the one hand between antelius and the European forms fuscus and argentatus and on the other hand between atlantis (incl. the Atlantic populations of michahellis) and the West European forms graellsii and argenteus; 3. that vegae and mongolicus make no contact with the pink-legged gulls of the American continent, the same being true of californicus; 4. that kumlieni whose affinity to glaucoides is evident, behaves as a species against smithsonianus; 5. that in West Europe the fuscus-group behaves as a species against argentatus (incl. argenteus) as well as against omissus; 6. that omissus where it occurs along the sea coast apparently does not interbreed with argentatus regularly. On the basis of these facts -including the fact, that argentatus is of American origin-, the writer is of the opinion that 5 species should be recognized, namely L. juscus, L. argentatus, L. cachinnans, L. californicus and L. glaucoides. This is in principle also the opinion of Dwight, Stresemann, Alexander and Voous, although the latter fails to separate specifically cachinnans from juscus. In the number of subspecies the writer suggests a simplification. He accepts the consideration of Voous (1959) that smithsonianus, argenteus and argentatus cannot be sufficiently clearly distinguished from each other. This also is the case with heuglini and antelius, with cachinnans and ponticus, with vegae and birulai and with intermedius and juscus. In this way the writer comes to the following classification of the species-group: 1. Larus juscus (juscus+ and graellsii) 2. Larus argentatus (argentatus and thqyeri) 3. Larus cachinnans (cachinnans, michahellis, atlantis, heuglini, mongolicus and vegae) 4. Larus californicus 5. Larus glaucoides (glaucoides, kumlieni). According to this system the Scheveningen gull would be named Larus cachinnans heuglini Bree 1876. 7. On June 12th, 1960, two gulls were observed along the southern dyke of the East Flevopolder, their behaviour suggesting that they formed a pair. The very large and darker male had bright yellow legs, the female lead grey legs. These two birds were seen again on July 10th at the same place. On June 26th, July 24th and 31st, 1960, once again a yellow-legged, slate-grey gull was observed there. From the wing markings and other characteristics was established that these observations concerned at least three and possibly five different birds, all differing from the Scheveningen gull. Furthermore, two yellow legged gulls were observed in the winter of 1960/61, one along the dyke of the East Flevopolder in December 1960 and the other in Scheveningen in January 1961. Both birds showed a pure white, unspotted head and neck. After discussing the characteristics of these birds the writer concludes that they too must be considered as belonging to the form heuglini. The very large and dark male of June 12th was a typical antelius, yet some of the other birds-being rather lighter-might is considered as dark specimens of taimyrensis. The lead grey legs of one of these birds might suggest a strain of birulai, the legs of birulai according to Stegmann being often pale bluish. For the sake of completion the writer discusses the question of whether the 'strange' gulls should not be considered as hybrids of argenteus X graellsii in reason of the fact that in the first years after the settling of graellsii (1926) in Holland such cases of hybridisation were repeatedly observed. From the study of Voous (1946) the writer concludes that only after repeated back-crossing with graellsii could a hybrid with a mantle as dark as antelius be obtained. He considers it practically out of the question that in the space of a few months seven (possibly eight) such (adult) hybrids could have shown up, some of them exhibiting moreover characteristics which neither argenteus nor graellsii possess. 8. Heuglin's Yellow-legged Gull, Larus cachinnans heuglini, is new to the Dutch list. As a species Larus cachinnans has been observed before in the Netherlands. In the Leiden Museum there is a mounted specimen -shot near Katwijk on January 25th, 1881-having yellow legs, a red eye-ring and very faintly spotted 'winter-head' and being hardly darker than argenteus. This specimen wholly conforms-even with regard to the white basis of the outer primary-to the form ponticus (= cachinnans) described by Stegmann. Furthermore the writer mentions the observation of 5 yellow-legged gulls detected by himself on February 18th, 1940, in Scheveningen. These birds too-hardly darker than argenteus should be determinated as cachinnans and came presumably from Finland or the Kola Peninsula ('omissus'). Finally the writer mentions several observations of (yellow-legged) 'omissus' made by Belgian ornithologists along the Belgian coast and the Braakmanpolder (Netherlands S. Flanders) almost exclusively in the months August and September. Of interest too is the observation of a yellow-legged gull in the Braakmanpolder on February 7th, 1960, three days after the Scheveningen gull was observed for the first time. This bird was considerably darker than 'omissus' and was possibly also heuglini.


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