Repertoire and structure of duet and solo songs in cooperatively breeding white-browed sparrow weavers

Abstract

Summary White-browed sparrow weavers (Plocepasser mahali) are cooperatively breeding songbirds of eastern and southern Africa that live in small groups year-round consisting of a dominant breeding pair, and subordinate, non-breeding males and females. This species possesses an elaborate vocal communication system: solo songs are exclusively produced by the dominant male, duet songs are mainly produced by the dominant pair, and chorus songs, similar in syllable structure and temporal pattern to duet songs, are produced by all group members. We analysed songs of males and females with known social status recorded from different colonies in Zimbabwe and complemented these data by studying songs of captive birds at our institute. Solo songs are produced in one performance at dawn during the breeding season. Recordings of captive males on consecutive days revealed that males sing in a single solo performance 88.4 ± 4.1% of their total solo song repertoire. This suggests that dominant males recorded in Zimbabwe have a solo song repertoire of 67.0 ± 4.0 syllables, which is similar in size to those of captive males (58.3 ± 3.7 syllables). Repertoire sizes of both free-living and captive males are not correlated with the length of the solo song performance. Duetting is both antiphonal and in unison. Dominant males and females appear to have similar sized duet repertoires (51.9 ± 2.1 syllables). Recordings from captive pairs suggest that 7598% of the repertoire is shared with higher syllable sharing in more experienced pairs. Since all group members engage in duets and chorus singing, we estimate that each subordinate male and female shares the duet syllable repertoire with the breeding pair. For dominant males, the duet syllables are widely distinct from those of the solo songs; of their total syllable repertoire only 2.1% occur in both repertoires. Further, solo song and duet song differ in the temporal organisation.