I took a few photos of Black-headed Gulls at Stranraer, Dumfries and Galloway. Most were cracking adult birds and they looked stunning.
The bird below is a second winter (2CY), judging from the black leading edges to primaries 9 and 8. What is unusual about this bird is that its five outer primaries are white (P6-10) along with the associated greater coverts and some of the smaller coverts as well. Normally only P7 to P10 are white. I know that some of the more eastern Black-headed Gulls can show this feature, so I wondered whether this could be a sibiricus bird. Not very likely, perhaps, but the weather at the time was well below zero... Maybe white P6 is a normal variant in ridibundus - anyone know?
(See this thread at Gull Research for comment on this bird, which suggests this is within normal but as yet undocumented variation for ridibundus)