Relative divergence of mobbing calls and songs structures in passerine birds

Abstract

AbstractDivergence and convergence in acoustic signals may be driven by different processes. Uncertainty about which of these processes best explains the patterns of acoustic variation between species has fuelled a long-standing debate in evolutionary biology. In particular, the features of acoustic signals are expected to vary according to their functional support. To compare the relative divergence of vocalizations according to their function, we examine two types of signals within 23 bird species, whilst controlling for species size, phylogeny and within-species variation: (i) mobbing calls emitted to recruit both conspecifics and heterospecifics against a predator and (ii) territorial songs, a signal playing an important role in sexual and social communication. We found that divergence of acoustic features varies according to their function (mobbing calls vs. territorial songs). Furthermore, species size influences spectral features, while phylogeny explained acoustic variation in only one of the variables measured: note richness. Finally, our results reveal that the acoustic characteristics can vary greatly within species, regardless of the vocalization type, indicating that such variations cannot be ignored when performing comparative analyses across species.