Song variation in west-Pyrenean chiffchaffs was thoroughly analyzed. Intrinsic physical structures of these songs as well as extrinsic contextual ones were processed simultaneously in qualitative and correspondence analyses. The aim was to assess objectively and to describe the song differences between collybita and brehmii, easily perceived in the field, accounting for variation within the groups due to other sources than taxonomic. All songs originate from the contact zone of the two forms, i.e. taxonomically still-undetermined entities. The following results were obtained:

  • 1
    The main source of song variation is confirmed to be the bird's membership in the collybita or the brehmii form. Each song type has been characterized in terms of physical variable values.
  • 2
    Within these forms, the songs emitted in the same social or temporal contexts are more similar than the songs produced in different contexts. This has been verified intra- and interindividually.
  • 3
    Some individuals have songs that share structures of both forms — these are the mixed-singers described by Thielcke & Linsenmair (1963).
  • 4
    In the sympatric zone, the acoustic differences between collybita and brehmii are strengthened by an acoustic character displacement.