Bird song serves as a critical medium for intraspecific communication, playing indispensable roles in mate attraction, territorial defense, and species recognition. As a complex learned behavior, bird song often exhibits significant geographical variation, which can be influenced by environmental factors, cultural transmission, and genetic divergence. The Common Chiffchaff (Phylloscopus collybita) complex, a widespread Palearctic passerine, is a renowned model system for studying evolutionary processes, particularly due to its intricate pattern of subspecies distribution and the existence of secondary contact zones where hybridization occurs. This study meticulously investigates the geographical variation in the song characteristics of three key chiffchaff subspecies: P. c. collybita (Western European), P. c. abietinus (Eastern European), and P. c. tristis (Siberian), focusing specifically on their distinct core ranges and two prominent secondary contact zones. We hypothesize that song parameters will exhibit significant differentiation among subspecies and reveal patterns of intermediacy or divergence within hybrid zones, reflecting ongoing evolutionary dynamics. Utilizing advanced bioacoustic analysis techniques, our findings reveal distinct vocal signatures for each subspecies and complex patterns of song variation within contact zones, suggesting both gene flow and potential reproductive isolation mechanisms. This research contributes significantly to understanding the role of acoustic signals in avian speciation and the dynamics of hybrid zones in a rapidly changing world.

Chiffchaff, vocalizations, geographic variation

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