Differences in song repertoire organization in two leaf warbler species (Phylloscopidae), the large-billed leaf warbler (Phylloscopus magnirostris) and the sulfur-breasted leaf warbler (Phylloscopus ricketti)

Abstract

Distinct song types that constitute the song repertoire can be identified in the singing of males of many passerine bird species. Song repertoires and the organization of singing in two Chinese species of leaf warblers (the large-billed leaf warbler and the sulfur-breasted leaf warbler) have been compared. The songs of both species are simple and belong to the common “archetype”, and the size of the individual song repertoire is usually small (6–7 song types in the former species and 7–9 in the latter). The time-and-frequency parameters of the notes that constitute the songs (five notes in each song) have been measured, and Euclidean distances between all song types of a specific male and a single species have been calculated using the data. The similarity (as inferred from Euclidean distances) between the songs in each individual large-billed leaf warbler male was almost twice higher than that between the songs of the sulfur-breasted leaf warbler individuals. Moreover, transitions to a song of a different type during singing (song type switching) were more frequent in large-billed leaf warblers. A negative correlation between the average Euclidean distance between all songs of an individual and the frequency of song type switching has been discovered. Males of certain bird species reportedly show a stronger reaction to song type switching than to switching between the versions of songs that show higher similarity (song types can be subdivided into variants in some species). Therefore, we assumed that large-billed leaf warblers are “compelled” to switch the song type more often in order to compensate for the scarcity of the code related to considerable similarity of songs of the different types.