NIEBOER E (1975) The Bonellis Warbler of Schiermonnikoog. LIMOSA 48 (1): 82-85.

Western Bonelli's Warbler Phylloscopus bonelli The conclusion by Voous (1972) that the Bonelli's Warbler trapped at Schiermonnikoog in 1969 belongs to the subspecies Ph. b. bonelli on account of its short wing (63 mm) is discussed. Although this character appears not to be decisive, his conclusion can be maintained, as the bird showed a wingformula which occurs nearly only in the subspecies Ph. b. bonelli.

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