Successive Sunday afternoon visits to Erith on the south side of the Thames late July into August, mainly coinciding with a rising tide, produced a couple of juvenile Yellow-legged Gulls, one of which very aggressive to other gulls when feeding. An older individual (1st summer to 2nd winter?) made a brief appearance.
An adult Caspian Gull stayed briefly on one visit, a couple of days after its first sighting. It soon headed down river.
More recently the following juvenile Gull made a brief visit, it headed up river at one point flying alongside one of the young Yellow-legged Gulls. First looks shows scalloped scapulars, dark tertiary block, and a black bill, but was it a fit for Caspian Gull? Maybe at best 'Caspish' Gull, the greater coverts shown in one of the video grabs, particularly the inner ones, not looking good for Caspian Gull. Is the underwing pale enough, or pale in the right places?
If this was late January and the following Gull was spotted, would it catch you out? I think it has fooled me in the past on Wennington Marsh, though I claim an unsubstantiated two bird theory! The structure and the adult bill betrays it as more than likely a leucistic Herring Gull. Sadly, I did not see it in flight, no sooner had it appeared on the jetty and it was gone.
Video footage of most of the above can be found on YouTube by clicking here.