DIJK K VAN (2011) Site fidelity of Black-headed Gulls Larus ridibundus during primary moult. LIMOSA 84 (1): 21-25.

Black-headed Gulls show a considerable fidelity to sites used for breeding and for wintering, but almost nothing is known about site fidelity during primary moult. This paper explores this subject by presenting the encounter history of two individuals. An adult ringed in Prague in March 1990 was observed in a city park in Groningen (53°13'N, 06°32'E, The Netherlands) in July-October of 18 subsequent years (Tab. 1). The bird was moulting its primaries in all of eight years for which moult records are available (Tab. 2). Dozens of examples of ringed adults present in city parks in two or more seasons suggest that site tenacity during primary moult is a common strategy. Huge numbers of moulting adults stay in the Wadden Sea during summer and in early autumn. The resighting history of an adult with site fidelity to Lauwersoog (53°24'N, 06°12'E, The Netherlands) is presented in Table 3. This bird moved to the city of Groningen (30 km to the SE) each winter after moulting at Lauwersoog. There are more records of adults with a similar site tenacity to Lauwersoog and also to the Wadden Sea island of Terschelling. Hence, site fidelity during primary moult is probably a common phenomenon in both marine and urban nvironments. #### Black-headed Gull Chroicocephalus ridibundus = Larus ridibundus

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