Structural-functional characteristics of two song types in Phylloscopus humei (Phylloscopidae)

Abstract

Several songbird species use two singing modes, which are functionally different. The first mode is preferentially used at the beginning of the breeding cycle, and serves to attract females, while the second mode is used later in the season as well as during territorial countersigning. The two singing modes are well known in many Parulidae species from North America. The repeat mode (type I songs) comprises repetitions of a single song type. The serial mode (type II songs) consists of several song types sung in a versatile sequence. In Eurasia, a similar acoustic behaviour is known in several Phylloscopus species. However, these data are still scarce. Additionally, it is not yet fully understood whether the song structure per se or the song bout organisation (e.g. song-type diversity) plays a primary role in communication of the aforementioned songbirds. In this respect, it could be useful to analyse acoustic behaviour of Phylloscopus humei because its males have only two song types, namely song type I and song type II. These song types differ greatly in structure. In this study, we used playback experiments to ask whether these song types differ in their function. The study has been conducted in 2019–2021 in the federal State Nature Sanctuary «Posarym» (Republic of Khakassia, Russia) at the beginning of the breeding cycle of Phylloscopus humei. While singing spontaneously, males predominantly use song type I. The use of song type II is increased immediately after playback presentation. In contrast, males did not increase the rate of song type II during the playback. Instead, they produced two call types at that time, which apparently serves as an aggressive signal. Our study has shown that the use of two song types is different. Song type I is predominately used for advertising the territory and attracting a female. In contrast, song type II is more often used in countersigning between neighbouring males, although not at a time of direct aggression, i.e. during the playback. Noteworthy, we also found that males can share song type II but not song type I from their repertoires. In turn, the song sharing is thought to play a role in male-male interaction.