La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

Titre :	Difficulties in determining the age of Common Terns in the field
Auteurs :	S. J. White, Auteur ; C. V. Kehoe, Auteur
Type de document :	Article
Dans :	British Birds (94(6) June, 2001)
Article en page(s) :	268-277
Résumé :	Large numbers of Common Terns Sterna birundo of known age were studied during the breeding season at Seaforth Nature Reserve, Liverpool, Merseyside. Detailed observations of key plumage and bare-part features were recorded, and compared with published criteria for ageing terns. It was found that the majority of second-summer birds were in full breeding plumage and were therefore indistinguishable from adults; and that many first-summer birds exhibited some breeding-plumage features and were therefore confusable with some second-summers. A few second-summer birds were in non-breeding (winter) plumage and were therefore inseparable from similar first-summers. It is concluded that no individual Common Tern, except those first-summers which retain juvenile features, can be aged safely, and we propose that ageing terminology be amended to take this into account. Previous estimates that only about 1% of first-summer. Common Terns return to the breeding grounds were confirmed, but, contrary to some previous studies, the majority of second-summers did so.

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