A fourth-winter type photographed at Dosthill Lake, Warks, on November 13th 2008. The slender, parallel-sided and pointed bill, with little evident gonys, suggests Caspian Gull, as does the greenish yellow base to the bill, with a brighter tip and a neat black-and-red subterminal band. Other Caspian-like features include the blackish iris (with 'bullet-hole' appearance) and streaking confined to base of the neck. On the image of the bird preening, there is black on the outer seven primaries, including a broken band on p4, and there are very pale (almost white) Caspian-like veins on the bases of the inner webs of the outer primaries. There is extensive white at the tip of p10 (see under surface visible in lower photo) but it appears to lack the prominent clean white tip of a good 'Pontic' Caspian Gull. The head-shape is not quite convincing for Caspian Gull, with a quite pronounced angle at the forehead and a rather flat crown. The legs are decidedly short for Caspian Gull, with little visible tibia, and they are quite bright 'Herring Gull' pink. On a good Caspian the legs are long (with evident tibia), rather spindly, and a paler 'washed out' greyish-pink hue. Is this bird simply a variant Caspian Gull with some argentatus-like traits or is it perhaps a hybrid, conceivably Caspian x Herring Gull? Caspian, Yellow-legged and Herring Gulls are now regularly hybridising in parts of eastern Europe and the possibility of such birds reaching the UK is real.

A high percentage of gull-watching here in the midlands is conducted at evening roosts, where identification of Caspian Gulls is often at relatively long range and is based primarily upon head and bill profile, iris colour (or lack of) and just basic details of the wingtip. Birds are infrequently seen preening, so precise details of wing-pattern are rarely discerned. Leg-colour is rarely discerned and leg structure is never discerned. Hence features which depart from the standard are less likely to be detected than when observing birds at daytime loafing and feeding areas. Those watching at such daytime sites, where a fuller suite of characters can be examined, are reporting a small but significant number of birds with ‘mixed’ characters. At landfill sites in Cambridgeshire, for example, Dick Newell has encountered several Caspian-like gulls with 'mixed' characters. Some of these have borne rings and each has proven to be a hybrid or to come from mixed colonies: see  www.magikbirds.com/image.asp?title_id=1102  for an example of a Caspian x Herring Gull.

Conversely, it would be an over-reaction to assume hybrid origin for any gull with features of Caspian Gull but which is less than truly 'classic'. A balanced approach has to be taken, while keeping a sharp eye out for any feature, or especially a combination of features, which really warn of possible hybrid origins.

See also photos of another debated 'Caspian Gull' at Stubbers Green and Chasewater in December 2008.

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