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Résumé :
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Count, recovery and biometric data were analysed to assess the conservation status and use of Teesmouth by Common Terns Sterna hirundo and Sandwich Terns Sterna sandvicensis in late summer. The recognition of the international importance of Teesmouth to migratory Sandwich Terns was endorsed. Peak late summer counts for 1990-1997 averaged 1,835, over 1% of the international population. Analysis of information from both Common and Sandwich Terns ringed or recovered in late summer at Teesmouth identified the existence of a trans-Pennine migratory pathway of Common Terns between Teesmouth and Merseyside. Trans-Pennine migration of Sandwich Terns is also suspected from visual observations of departures from Teesmouth. 55% of adult Common Terns using Teesmouth have yet to initiate primary moult. This, and the recovery patterns, are consistent with the involvement of a substantial Baltic contingent of non-moulting adults amongst the late summer Teesmouth population. Of those adults in active wing moult, primary moult had progressed less far than for birds in the Wadden Sea at the same time of year. This suggests a cline through northern European breeding populations in the timing of moult. Visible migration, retrap data, arrival dates of different populations and the progression of primary moult, all identify rapid turnover amongst the late summer Common Tern population at Teesmouth, suggesting that over 1% of the UK breeding population, with their young, migrate through Teesmouth.
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