LBBG 4cy: Bruxelles L- 93303, April 06 2003, Dintelhaven - Maasvlakte, the Netherlands.

An adult with a Bruxelles ring but of uncertain origin, since it has been caught (as an immature) on a landfill and ringed on that occasion. Ringed as 2cy at Antwerpen, Belgium (51.21N 04.46E) on July 22 2001.
Compared to other LBBG which were present in the direct surrounding, this 4cy showed an average tone of grey on the upper-parts in the colony, not obviously paler as expected in westernmost graellsii. Ring projects revealed that adults from the UK and Belgium may turn up in Dutch colonies and start mixed couples. 
This bird has a clear yellow bill, without black on the upper mandible. Note however the immature lesser coverts and the inner greater coverts, indicating this is a near-adult (4cy or 5cy). Most other feathers are neat grey and the partial spring moult of the upper-parts has been completed.