Abstract
Vocalisation is generally considered a reliable way to separate several taxa within the chiffchaff complex; for example, both ‘Siberian Chiffchaff’ Phylloscopus collybita tristis and Iberian Chiffchaff P. ibericus give distinctive songs and calls when compared to each other and to nominate Common Chiffchaff P. c. collybita and ‘Scandinavian Chiffchaff’ P. c. abietinus. As part of a wider study of chiffchaffs in the Netherlands, two birds were detected which gave calls that did not match with their morphology or genetic identification. These two birds – a Siberian Chiffchaff calling like a nominate or Scandinavian Chiffchaff and a nominate Common Chiffchaff calling like an Iberian Chiffchaff – are detailed in this paper.