Extension of post-juvenile moult and ageing of the Cetti's warbler Cettia cetti  in northern Italy


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The extent of the post-juvenile moult of Cetti's warbler was studied in northern Italy. Compared to previous studies, it was found to be more extended than in northem Europe populations, involving body feathers and most of wing coverts. Moreover, juvenile birds moulted rather frequently all the tertials and up to 5 inner secondaries. In 6 cases out of 102 examined (4.9%), also 2-5 primaries were moulted. Birds frorn first clutches moulted significantly more greater coverts than birds from second clutches. Extension ofthe post-juvenile moult was significantly correlated with the degree of skull pneumatisation in September and October, suggesting that birds from early clutches have a more extended moult. Moreover, males moulted on average significantly more remiges and greater coverts than females. Moult limit. i.e. the contrast between moulted adult-like feathers and unmoulted juvenile feathers. was visible in all examined juvenile birds within greater coverts or, altematively, within tertials or secondaries. Pre-nuptial moult was restricted both in terms ofindividuals and number offeathers involved, and never affected wing coverts or remiges. On the basis ofthese results, a new method for ageing Cetti's warbler, based on the contrast between moulted and unmoulted feathers, is proposed. This method allows juveniles to be told apart from adults beyond the completion of skull pneumatisation, until their first complete moult.