Unidentified predatory seabird on Thames?

[Andrew1]

I need help identifying a predatory seabird, possibly a non UK resident seagull, feeding on a small duck on the Thames at Kingston yesterday. I know my great backed and lesser backed gulls and it certainly was not one of those, although it was of similar size. It was bright white with distinctive black spots/blotches not a juvenile gull which is a grayish colour. This seabird was stark white. But the beak was what ruled out a large UK predatory gull - it was jet black, thinnish and pointed, not at all like the hooked, solid looking yellowy coloured ones of the UK's two largest gulls. It was midstream and busy pulling out the long string like entrails of an upturned duck until a passing boat scared it off. i have had no luck scouring google images!

[captaincarot]

have you considered a skua

[~T~]

http://www.rspb.org.uk/wildlife/bird...ull/index.aspx

Or

The RSPB: Glaucous gull

Maybe?

[aeshna5]

The mention of the black blotches on the upperparts + the all dark bill sound like a good description of a 1st winter Great Black-back + the behaviour is pretty typical too.

Neither skuas or Glaucous Gull really fit the description + Great BB a more regular species for that area.