12cy M90, Missouriweg - Maasvlakte, the Netherlands, April 29 2002.
An adult bird ringed left white M90, ringed as pullus at the nest, July 6 1991, now in 12cy. These codes were used from the first years the ring project started in 1990 and 1991. There is also a vertical T on the ring. Both green and white rings were used in the early 90's, but green rings haven't been rediscovered for the last two years. They are probably too worn by now and are lost, unlike the white rings. In white rings, no pigmentation is used and therefore these rings last longer.
Note the hint of black markings on the bill.