By Joan Castelló Massip and Marcel Gil-Velasco
Abstract Iberian Chiffchaff Phylloscopus ibericus has become an annual vagrant to Britain, but in some cases the identification of this subtle species remains extremely challenging. First-winter Iberian Chiffchaffs undertake a partial moult on the wintering grounds, which includes the primaries, while adult Iberian Chiffchaffs do not moult primaries during their partial winter moult. A moult limit in the primaries is thus a key ageing criteria for Iberian Chiffchaffs in spring. Since neither age class of Common Chiffchaff P. collybita replaces the primaries during the partial winter moult, the presence of moulted primaries in spring is a potentially useful identification feature for Iberian Chiffchaff. We present data from spring birds at the Llobregat Delta, Spain, to quantify the extent of moult in 2CY (first-summer) Iberian Chiffchaffs.
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