Primary moult in Iberian Chiffchaff as a means of ageing and identification

Published on 05 August 2017 in Main articles

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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Iberian Chiffchaff, Titchwell, Norfolk, April 2011. This vocal male was initially identified by its distinctive song. With good photos such as this, the extent of primary moult can be assessed, thus establishing it to be in its second calendar-year (first-summer). The winter-moulted P6–P9 (highlighted) appear distinctly darker, broader, and less worn than the comparatively browner and narrower inner primaries (P1–P5), which are retained juvenile feathers. This bird, the second at Titchwell in as many years, was initially assumed to be a returning individual, but the moult limit between the old juvenile and fresher moulted primaries show that it is in its first summer, and thus cannot be the same individual from the previous year. Andy Thompson