DIJK K VAN (1989) Current research: About ringed Black-headed Gulls in the city. LIMOSA 62 (2): 101-102.

Black-headed Gull Chroicocephalus ridibundus = Larus ridibundus In winter large numbers of Black-headed Gulls reside in cities. If in any park bread will also run off a piece trying to steal. usually these birds are not shy and attentive observer will see that occasionally a specimen ringed get around. It appears possible the inscriptions on metal or aluminum rings to decipher. In the city Groningen is already done since 1978 with the aim understanding of factors such as origin, population structure, site fidelity and residence

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