torsdag 25. oktober 2012

Hybrid herring gull x caspian gull?

This striking adult gull was seen in pouring rain for a few minutes october 3rd 2012. It is not easy to exclude caspian gull on the standing gull. Amber eyes - mostly white face with head streaking mostly concentrated in the neck - long, slender greenish bill with little pronounced gonys angle (and the gonys angle very close to the tip) - pale yellowish legs - head shape and general build all point towards caspian gull. The open wing, however, reveals black on outer web only on P5. This wouldn't exclude caspian within the caspian range since about 10 % lack a complete band on P5 (according to Gibbins et al 2012). In a norwegian context, however, a complete band on P5 is probably a prerequisite for claiming caspian gull. Apart from the P5 pattern, the eye is in the pale end for caspian, the bird is maybe a little bit short legged, a tiny bit too streaked in the head and perhaps not extreme enough in the body shape to be a true caspian? Sooo, a hybrid?

Compare build with the herring gulls. Really easy to pick out from the crowds...

Black on outer web only on P5 probably excludes caspian gull in a norwegian context.


I guess there is no point asking for comments...

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