Identification of American Herring Gull in a western European context

Identification of American Herring Gull in a western European contextGull L californicus, Iceland Gull L glaucoides,Thayer’s Gull L thayeri and Glaucous Gull thanto Largentatus, their results thus supporting theCSNA hypothesis. Crochet et al (2002) held backfrom unreservedly recommending that smithsonianusbe regarded as a full species, preferring towait until their results were confirmed usinglarger sample sizes of all North American taxa.Additional unpublished data gathered by severalindependent research teams (Pierre-AndréCrochet in litt) confirm the earlier findings andhave led to the formal recommendation by theAssociation of European Rarities CommitteesTaxonomic Advisory Committee (AERC TAC) thatAmerican Herring Gull be treated as a species,Larus smithsonianus.Commenting on the taxonomic position ofEuropean Herring Gull populations, the CSNA(Sangster et al 1998) stated that ‘there is no evidencethat the form ‘argenteus’ is diagnosablydistinct from argentatus’ and concluded thatargenteus was conspecific with argentatus. Wequestion the supposed lack of evidence thatargenteus is not diagnosably distinct from argentatus.From our perspective, argentatus-types andargenteus-types are often readily separable in thefield (plate 23 and 35) and appear to fulfil sufficient‘requirements of diagnosability’ to merittaxonomic recognition.We prefer, therefore, to treat argenteus as adiagnosable taxon. While we realise that, inreality, the variation in European Herring Gullseems to be much more complex than the simple‘argentatus’ and ‘argenteus’ model, we do notknow if much of the yet-to-be explained andquantified variation has a particular bearing onthe identification of smithsonianus in Europe. Inthis paper, we follow the conventional arrangement,whereby L a argentatus refers to theHerring Gull which breeds in Fennoscandia,around the Baltic and White Seas and L aargenteusrefers to the on-average slightly smaller andlighter-mantled type which breeds in Iceland,Britain, Ireland and from Brittany, France, toapproximately southern Denmark – although itapparently forms a mixed population withLaargentatus in the area ranging from the northof the Netherlands to southern Denmark (Barth1975); the term ‘European Herring Gull’ is usedto refer to L aargentatus/argenteus.While it is beyond the scope of this paper todiscuss further possible (sub)specific variationwithin smithsonianus, it seems likely, given thecomplexity of ‘herring gull’ taxonomy in an area1 American Herring Gull / Amerikaanse Zilvermeeuw Larus smithsonianus, juvenile, Cape May, New Jersey, USA,September 1996 (Pat Lonergan). Individuals as dark as this one should not pose any identification problems in Europe.3