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Tuesday, 18 January 2011

Comparable sub-adult 'SLATY-BACKED GULL' from California

Here's a 3rd-cycle (by brown greater coverts and bill) SBGU accepted in California that appears darker backed and certainly paler eyed than the London bird

It strikes me that the head streaking of the London bird may also be a sign of hybridism for a 4th+ cycle bird, that of vegae being darker, age for age, than SBGU. I also agree with you (contra Lethaby) that the back color seems to vary a lot in these gulls, whatever they are, at least according to what the Japan sites identify as Slaty-backed. In the end I still think the biggest issue is that nobody seems to know how to define a pure Slaty-backed Gull (Peter Pyle)