| Summary: | In 2000, simultaneous counts of gull roost sites in Flanders were started for the first time. Until now, three counts have been organised, always at the end of January- beginning of February.We received data from 25 different roost sites but some of these were not visited at all three counts. The total number of counted gulls varied between 166,522 in 2001 (15 roost sites counted) and 249,557 in 2002 (20 roost sites counted). Bringing some gaps into account, we can assume that the number of wintering gulls in Flanders can exceed 300,000 birds. During all counts, Black-headed Gull Larus ridibundus was the most numerous species (max. 126,513), followed by Common Gull Larus canus (max. 92.432) and Herring Gull Larus argentatus (max. 17.822). Because not all roost sites along the coast have been counted, the numbers of Lesser Black-backed Gull Larus fuscus and Greater Black-backed Gull Larus marinus were relatively small. Only two roost sites held more than 20,000 gulls on average: the water reservoirs at Woumen-Merkem (70,026 gulls) and at Kluizen (33,668 gulls). Beside these water reservoirs (good for 48 % of all gulls counted), also harbour areas (28 %) and sand pits (18 %) were favourite roost site habitats. Natural habitats as salt marshes and flooded grasslands were less important. Although these roost site counts can give a good picture of the actual number of gulls present in Flanders at a certain moment, it remains unclear wether these data can be used for monitoring purposes. Further study and new counts in the coming years are necessary to answer this question.
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