| Summary: | In 1999, a colour ring-project on Herring Larus argentatus and Lesser Black-backed Gull Larus fuscus was launched at the Belgian coast. In total 509 and 486 Herring and Lesser Black-backed Gulls respectively, were equiped with colour rings. Both chicks and breeding adults in the colony of the outer harbour of Zeebrugge (West-Flanders) were ringed. Also some Herring Gull chicks from roof-nesting birds in Ostend (West-Flanders) and wintering birds from different places at the Belgian coast were equiped with a colour ring. In this article an overview of the distribution and migration patterns is given for both species. Most of the recoveries are from Belgium, France and the Netherlands. Lesser Blackbacked Gulls are reported from the coastal areas in Southwestern Europe and Northern Africa. Some colour ringed individuals from both species are seen in Germany and the United Kingdom. Outside the breeding period, Herring Gull from this study stayed close to the colony with the Dutch Delta-area, the coastline of Northern France and the Belgian coast itself being the most important. Besides a clear southward migration, some Belgian Herring Gulls also migrate to the north. Other populations from the northwest European continent show a similar northward migration, although this is less pronounced in the nearby breeding population of Schouwen in Zeeland (the Netherlands). In spring immature birds return later to the breeding grounds than adults. The Belgian Herring Gulls tend to visit rubbish dumps less frequently in the course of their lifetime, suggesting a change in food choise. Lesser Black-backed Gulls from Zeebrugge show a tendency to winter closer to the natal colony when getting older.
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