Mobbing calls of seven species of Parids under the paradigm of the FME-D combination

Abstract

Abstract The combinatorial properties of birds’ mobbing calls provide a focus for understanding signal evolution in the higher vertebrates. Indeed, when mobbing a predator, several Parids produce a combinatorial call: first, frequency-modulated elements (FME) followed by broadband frequency notes (D notes). No quantitative data is present in the literature to confirm the ubiquity of this combinatorial call in Parids’ mobbing calls. In the present study, we recorded sequences of seven species and analyzed whether (1) the dichotomy between FME and D notes stands for all species despite the large variation in acoustic properties found between species, and (2) whether the FME-D call is pervasive in mobbing situations. FME and D notes were efficiently labelled and clustered in each species because of their large differences in peak frequency and bandwidth. Modulation and duration, in contrast, were not useful for all species. With the help of a machine learning program, we analyzed the organization of the calls produced by the seven species. Six of them used FME-D calls more than chance but the coal tit P. ater rarely produced FME-D calls. No other particular call combination was predominant in all of the seven species (e.g. D-FME calls). These results pave the way for comparative research on combinatoriality in Parids to better understand to which extent birds process combinatorial rules.