Thursday, 11 December 2008

Gull sp.

Here is another photo of a large white headed gull which I have chosen to label 'Caspian-type'. As this bird has generated a little bit of discussion I got a bit worried and gave it some more thought.

The reason why I think this bird is not a 2nd Yellow-legged Gull is as follows: a) Lacks a darkish 'eye' mask thus appearing distinctively 'white-headed'. b) p10 mirror in 2nd win is a Caspian feature and not Yellow-legged Gull, c) structurally I interpret this bird as being 'long-necked' and perhaps even small headed, not much of a tertial step and maybe even a hint of a full breast- all more Caspian features but I wouldn't put too much emphasis on my subjectivity with structure on a bird like this d) Also perhaps the dark tip, pale based bill and dark eye- maybe (?) pointers towards Caspian.

To my eyes, I don't think there is too much to suggest argentatus- the white head, dark eye, lack of blue grey in the upperparts, structure etc but some people have suggested they can see argentatus in it.

Therefore, as it shows Caspian features- why not a Caspian. Well, I would prefer not to call anything a Caspian unless it is a classic. Malling Olsen and Larsson's 'Gulls' deal with Caspian Gull- condensing a lot of independent papers and discussions into a concise summary- so I think Caspian Gull identification has become easier in recent years. Basically if it don't look like the birds in plates 42 and 43 it isn't one. I cant find this latest Beddington bird in this book- so...good night to that particular bird.

This book has even been endorsed as 'high standard' by the BOURC Taxonomic Sub-committee (TSC) (BB:101 pg 344) so I think can pass for 'scientific'. Although I am not too sure if my game of 'snap' qualifies as such.

That may be over-simplifying things but there are still gaps in knowledge about the variation within Caspian Gull and there appears to be hybridisation between Herring (argentatus)-Caspian at least in central Poland and also there are birds showing mixed characteristic from the Volga to Scandinavia. Therefore it appears a good idea to be cautious when assigning the name Caspian Gull unless it is a classic. The sink term 'Caspian-type' is a bit of a cop out but just points towards Caspian when it shows more features than say Yellow-legged so maybe a convenient way of logging these birds. Perhaps it is even more appropriate to call this bird gull sp. but personally I feel we can narrow it down just a little bit more. Of course, I could be wrong.

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