ИСТИНА

It is well known that transitions between different song types in a song sequence are non-random in many species, but the signaling significance of non-random vocal streams is poorly understood. Here, we firstly analyzed the song sequencing rules in spontaneous singing and then simulated territorial intrusion by broadcasting conspecific songs in territories of three closely-related sympatric and morphologically extremely similar species: Martens’s Warbler (MW: S. omeiensis, n=8 males), Grey-crowned Warbler (GW: S. tephrocephalus, n=10) and Bianchi's warbler (BW: S. valentini, n=11). The study was conducted in April-June 2016 in Hupingshan National Nature Reserve (Hunan province, China). Males of all species had a repertoire of 13–64 song types. While singing spontaneously, MW and GW produced song types according to fixed sequences. By contrast, the ordering of song of BW looks like a more random process which was revealed by information theory approach. A comparison of spontaneous singing with that elicited by playback showed that the transitions between different song types of BW in a song sequence were determined more by specific factors and predictable and thus more non-random. By contrast, the song sequences rules of MW and GW did not differ between spontaneous singing and singing in response to playback. Our results are thus consistent with the idea that nonrandom vocal structures could play a role in male–male competition but the pattern was hidden in species with extremely nonrandom spontaneous singing (i.e. MW and GW). The study was supported by the Russian Foundation for Basic Research (project 17-04-00903-a).