Bonaparte's Gull in Eastbourne

I headed down to Eastbourne for a leisurely few hours by the seaside with David B. We ditched a car at Dartford where, coincidentally, there were 8 Waxwings and the showy Slavonian Grebe continued its residence on its favoured pool. It was late morning by the time we arrived at Princes Park, and there had been no sign despite all the long lenses. Within five minutes, I found the Bonaparte's Gull and this quality little, tree-nesting yank gull put on a show for the next few hours and often, I targ: -

As you can see, it proved rather obliging and its high-pitched call could be heard at times, taking me back to the flocks I saw in Canada last December here. It does have extensive black feathering in the inner primaries (to P3) - a feature potentially of a second-cycle (so third calendar year) bird; however its primary coverts and alula were unmarked so probably best to age it as an adult. Not much else about, and getting back to London with a couple of hours of light left produced little of note; just one NTGG ringed Herring Gull at Crayford. Grim weather forecast tomorrow but I'll still be getting amongst it - last day of British birding as I'm off to California next Saturday for some serious yank gullage.