Geographical variation in chiffchaff song: across three subspecies and two secondary contact zones

Abstract In many bird species, such as the common chiffchaff Phylloscopus collybita , the geographic variation in song is a crucial factor in determining intraspecies diversity. However, capturing this variation in trans‐Palearctic species can be challenging due to their wide ranges. We present an almost continent‐wide study spanning from Germany to Yakutia, covering Western European, Eastern European, and Siberian chiffchaff subspecies, and including a broad zone of hybridization between the latter. The novel fine‐scale differentiation patterns are revealed through a detailed analysis of local repertoire variability, including the diversity and geographic distribution of syllables, coupled with quantitative measures of rhythmic structure, frequency, and temporal song characteristics. Our study shows pronounced geographic variation across the entire chiffchaff range, with a distinct eastward trend characterized by an increase in singing speed and vocal repertoire size, a decrease in both the maximum and minimum frequencies, and a higher proportion of syllables with ascending modulation.