Song Divergence in the Group of “Brownish” Chiffchaff Forms (Phylloscopus collybita sensu lato)

Abstract

Study of the geographic variability of bird song is important for understanding the evolution and taxonomic structure of polytypic species with extensive and complex distribution areas. The chiffchaff is among such species. Several allopatric and parapatric forms inhabit the space of its trans-Palaearctic range. They vary in body size and vocalization, and, in accordance with the plumage color, they can be divided into two groups: "greenish" and "brownish." We made a comparative analysis of the song of three allopatric "brownish" forms (lorenzii, sindianus, and tristis), as well as one "greenish" form (caucasicus), which is sympatric with lorenzii (the only case of almost complete sympatry of different forms of chiffchaff). Significant differences were found in a number of phonetic and syntactic song parameters. Complete separation of the forms studied can be made according to the maximum frequency of the song and the speed of its performance (the number of notes per second). The sindianus form stands out for its relatively high-frequency and broadband song. The tristis form shows the lowest frequency song and the narrowest range. It is also the leader in the speed of performance of the song (up to 6-7 notes/s). The number of notes with a rising modulation is the maximum in tristis and the minimum in lorenzii; no such notes exist in caucasicus, like in other "greenish" chiffchaffs. The differences are discussed in light of the hypothesis of "acoustic adaptation" and in connection with the taxonomic relationships between the different forms of chiffchaff.

Bioacoustic differentiation of calls in the chiffchaff complex

“…The subspecies tristis is also the most distant geographically to most of the other species or subspecies, particularly to P. canariensis , with which it showed the greatest differences in call traits. The higher similarity of P. c. tristis with P. s. lorenzi than with other P. collybita subspecies is consistent with the divergence patterns shown by song and morphological (brownish plumage) characters ( Helbig et al, 1996 ; Ilina et al, 2021 ) but contrasts with those according to molecular traits, that show P. c. tristis as closer to other P. collybita subspecies than to P. s. lorenzi ( Helbig et al, 1996 ; Raković et al, 2019 ). Genetic analyses ( Helbig et al, 1996 ; Raković et al, 2019 ) agree however with analyses based on phenotypic characters (this study; Helbig et al, 1996 ; Ilina et al, 2021 ) in showing P. c. tristis as the most differentiated subspecies, which led ( Raković et al, 2019 ) to argue that it may represent a separate species or at least may be in a stage of incipient speciation or semispecies status ( Helbig et al, 2002 ).…”

“…The higher similarity of P. c. tristis with P. s. lorenzi than with other P. collybita subspecies is consistent with the divergence patterns shown by song and morphological (brownish plumage) characters ( Helbig et al, 1996 ; Ilina et al, 2021 ) but contrasts with those according to molecular traits, that show P. c. tristis as closer to other P. collybita subspecies than to P. s. lorenzi ( Helbig et al, 1996 ; Raković et al, 2019 ). Genetic analyses ( Helbig et al, 1996 ; Raković et al, 2019 ) agree however with analyses based on phenotypic characters (this study; Helbig et al, 1996 ; Ilina et al, 2021 ) in showing P. c. tristis as the most differentiated subspecies, which led ( Raković et al, 2019 ) to argue that it may represent a separate species or at least may be in a stage of incipient speciation or semispecies status ( Helbig et al, 2002 ). In support to its subspecies status is the mass hybridization and significant gene flow that occurs between P. c. tristis and P. c. abietinus in secondary contact zones, as well as the responses of territorial males to the playback song of the other taxon ( Shipilina et al, 2017 ; Marova et al, 2017 ).…”

On the taxonomic status of the Siberian Chiffchaff Phylloscopus [collybita] tristis (Phylloscopidae)

“…The song of tristis is also strikingly divergent from the song emitted by the Common Chiffchaff. The song of the western subspecies of the Common Chiffchaffs is fairly well described by its onomatopoeic English name ("chiff-chaffchiff-chaff") and is composed of a simple succession of near-identical notes which appears as descending on sonagrams, whereas tristis emits a much faster, complex, lower pitched and varied song comprising several types of ascending and descending notes (Figure 1; Martens & Meincke 1989;Marova et al 2017). Il'ina et al (2021 measured various song parameters and analysed song divergence between P. sindianus sindianus, P. s. lorenzii, P. [c.] tristis and P. c. caucasicus.…”