Here are a few ringed Black-headed Gulls that I had on the Thames last week ...
1) Adult yellow ' 2PJB', Barnes, 5 December. Ringed at Pitsea, Essex, in March 2016. More details here.
2) Adult white 'EE5T', Fulham, 5 December 2016. Ringed as an adult at Griend, Netherlands, on 6 June 2016. First recorded in the UK at Hyde Park, London, on 19 October before my sighting in Fulham.
3) Adult metal 'HV11.766' ringed as pullus at lake (55.1192, 23.7542) north of Kaunas, Lithuania, on 18 June 2011. Not recorded subsequently until in Chiswick on 2 December 2016!