Rattling cisticola song features and variability across sub-Saharan Africa

Abstract

Quantifying bird song variation can be an important tool for ensuring accurate species identification and can provide a significant basis for understanding the evolutionary processes that shape phenotypic diversity. This study describes variation in the songs of rattling cisticolas Cisticola chiniana across sub-Saharan Africa. For many cisticola species, learned songs are the most obvious phenotypic indicators of species affiliation and may also function to indicate individual quality. We examined 957 songs recorded from 61 individuals and archived in sound libraries. To assess the diversity of syllable and song types, we examined patterns of syllable use. We also measured vocalization frequency and time parameters and assessed how they vary through space. Results indicated that rattling cisticola songs are highly variable, but also have features that are species-specific. Examined songs had a relatively fixed structure containing one of three characteristic introductory note types, followed by an end phrase. Two of the introductory note types were sung across the species' range (some 4500km), whereas the third was only recorded in south-western Africa. End phrases generated most of the diversity in songs and appeared to have an unlimited number of forms. End-phrase characteristics showed a strong geographic variation, but did not vary with elevation. Song features varied individually and geographically in ways that are consistent with evolution due to multiple selective pressures, including stabilizing selection for species recognition on the introductory notes and diversifying selection on the end phrases. This pattern of lability in some song features coupled with stability in others may be a common feature of cisticola songs as it has also been found in Cisticola erythrops, a congener with a similarly broad range. © 2012 The Zoological Society of London.