Baltic Gull L f fuscus
1-3: © Ruud Altenburg, 25-06-05. Amsterdam, Netherlands.
There is a wide variation in moult patterns found in those 2cy fuscus which return to Europe. The first Finnish birds in this section represent the common, advanced birds. Red CRK4, from Pietarsaari
(63.38 N, 22.30 E), is an example of the least advanced 2cy fuscus observed in Europe. It shows a moult pattern identical to many graellsii: many wing coverts, tail, secondaries and primaries are still juvenile. The inner primaries have been dropped so the first complete moult has commenced, when pictured here in late May. The renewed scapulars and wing coverts are quite dark but without its ring it would be impossible to separate this fuscus from intermedius, e.g. compare to this Norwegian bird. For more pictures and information about CRK4, please see Ruud Altenburg's site.
It is more than just coincidence that these two fuscus found in the Netherlands are of the less advanced type? On simple probability grounds, we might expect that the more typical (and therefore frequent) advanced types are the ones most likely to be found at out of range locations. Most fuscus winter in E and C Africa, with smaller numbers in W Africa and the Middle East. Jonsson (1998) argued that the extensive moult of the most typical fuscus is at least partly a response to the harsh conditions in these equatorial areas, conditions which hasten feather wear. It is therefore tempting to speculate that birds wintering in more northerly and, for fuscus, less normal areas may be the ones that undergo a less extensive moult. It is also tempting to suggest that birds wintering in areas such as Morocco are the ones that get caught up with migrating graellsii and intermedius and, hence, are more likely to end up in places such as Amsterdam. This is a rather convenient model that explains the presence in the Netherlands and the moult patterns of CRK4 and CJC9. However, we are dealing with such small sample sizes that, at present, it is difficult to defend this model. Much more work is needed, tracking and monitoring the moult of ringed birds wintering in different areas.