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Yesterday I had a short visit in the colony Maasvlakte near Rotterdam, and could take a few images of ringed birds and immature birds keeping territories. It is still one of the largest colonies, but many things are changing. Due to construction works, the older parts of the colony have been abandoned by quite a few birds now, which moved to more recently claimed areas. Many birds holding territories and prepared their nests, but still not too many nests with full clutches (3 eggs).

The tibia rings were attached by Hans Keyser and Roland-Jan Buijs, birds trapped as breeding adults.
10cy Red C88 was ringed as pullus by Norman van Swelm, 7 July 2003.
16cy Green EX60 was ringed as pullus by Norman van Swelm, 21 June 1997.
7cy Blue DZAH was ringed as pullus by INBO at Zeebrugge, 16 July 2006.

A few more rings, still present:
15cy TU5 white & 15cy TJ4 white were ringed as pulli by Norman van Swelm, 8 juli 1998.
16cy EX13 orange was ringed as pullus by Norman van Swelm, 3 juli 1997.
6cy Blue GFAW was ringed as pullus by INBO at Zeebrugge, 10 July 2007.

And a slightly darker bird, without a ring....

Birds in the Netherlands linger around in a wide area around the colonies (it is still freezing -3 C at night and a bit of snow). Today at Voorhout:
14CY E301 red, ringed as pullus July 04 2000 at Maasvlakte, the Netherlands.

07 April 2013, finally after a long cold period, some sun. Still not too many birds in the colony...

HG BLB H-153713 is from Belgium now breeding here (about 7CY).
HG orange GY is breeding adult 05 May 2006 at Moerdijk, now moved to Maasvlakte.
LBBG red B35 is pullus ringed 2002 from the very same location as where I saw it now (less than 50 meters apart, though the area completely changed).