A beautiful second-calendar year (presumed) Baltic Gull Larus fuscus fuscus was present today at the sand suppletion works at Noordwijk aan Zee, The Netherlands.
Presumed 2nd-calendar year Baltic Gull. Noordwijk aan Zee, The Netherlands, 22 Jun 2013.
Presumed 2nd-calendar year Baltic Gull. Noordwijk aan Zee, The Netherlands, 22 Jun 2013.
Presumed 2nd-calendar year Baltic Gull. Noordwijk aan Zee, The Netherlands, 22 Jun 2013.
Presumed 2nd-calendar year Baltic Gull. Noordwijk aan Zee, The Netherlands, 22 Jun 2013.
Presumed 2nd-calendar year Baltic Gull (center, bottom) among Lesser Black-backed Gulls and Herring Gulls. Noordwijk aan Zee, The Netherlands, 22 Jun 2013.
Presumed 2nd-calendar year Baltic Gull. Noordwijk aan Zee, The Netherlands, 22 Jun 2013.
Why presumed?
Baltic Gulls are a rare species and can officially only be determined when a proven background is available (meaning: it has to be fitted a ring and has to have a known background). However, because of their advanced moult sequence compared with Scandinavian Lesser Black-backed Gulls Larus fuscus intermedius and Western Lesser Black-backed Gulls Larus fuscus graellsii, Baltic Gulls of a certain age and during a certain time of the year can be determined down to sub-species with a high degree of certainty.
This is certainly true for second-calendar year Baltic Gulls in the month of June. The individual in the photos shows a distinctive yellow bill and yellow coloration in the legs, but this also occurs in similarly aged graellsii and intermedius. What sets it apart though as a pretty much definite Baltic gull are the fully replaced wing coverts, secondaries, primaries and tail feathers.
References
Field identification criteria for second calendar-year Baltic Gull
Gulls to the Horizon 
Update: I now think we actually saw 2 different Baltic Gulls: https://gullstothehorizon.wordpress.com/2013/06/25/2-baltic-gulls-instead-of-1-at-noordwijk-20130622/