Phenotypic variance in an acoustic signal: a potentially sexually selected behaviour in Cape Clapper Larks Corypha apiata

Courtship displays provide important insight into sexual selection, evolution and the roles of communication signals in behavioural ecology. Any trait indicating individual quality must display phenotypic variation. Studying this variation can provide insight into the uses of acoustic cues in intra- and intersexual competition. We used the elaborate, understudied acoustic aerial display of the Cape Clapper Lark Corypha apiata to explore the relationship of display and nesting site quality parameters, to assess its potential role in sexual selection. We quantified the differences between individuals by estimating the repeatability of the bioacoustics of the display (claps, call). We then tested for the correlation with proxies of territory quality (area, arthropod prey biomass, Protea plant density). The song and clapping duration showed moderate repeatability, Protea density was negatively associated with the clap duration and the number of claps. There were no associations between the call parameters, the territory size and prey biomass. Wing clapping thus could play a role in sexual selection in this species, and our study provides a platform for future investigation of non-vocal acoustic signalling in birds.