first calendar year: September

Year 2000 we did a small survey on juvenile LBBG and moult (n=45). This year the survey was repeated and was done inside the colony in August. For the results, see the Juvenile LBBG August Section. 

By September, the large majority of juvenile LBBG have left the Netherlands and must have moved south towards Portugal. Many of the Dutch juveniles, which were seen moulting the scapulars in the colony (in August) must have joined these migrating groups. Nevertheless, many juveniles can still be found in the Netherlands, but as September progresses, more juveniles from Scandinavian colonies move in. This may be a reason for the "observed stand-still" in moult progress in juveniles: those local juveniles with advanced moult move south and less advanced individuals from Scandinavia fill the open positions or gather in mixed local groups.

Best option to reduce this problem is simultaneous counts throughout the West European coastline, or counts which only involve ringed individuals (thus from certain origin).
The problem of later hatched intermedius, moving into early moulting graellsii-groups is not a problem restricted to juveniles. To get a clear picture about arrested primary moult in autumn in adult graellsii plumage, the best place to look for these adults is probably outside the Netherlands, at the first major stop-over sites in Portugal for instance. It is believed that particularly those adults, which arrest primary moult, may also be keen on migrating south as quick as possible.