Context-dependent organization of birdsong: Experimental evidence from the collared flycatcher, Ficedula albicollis

While acoustic signals are highly flexible, their context-dependent changes remain poorly understood. Birdsong is a model of choice to explore these aspects. As repetition and diversity of song elements largely determine the overall characteristics of signals and such song characteristics as versatility and repertoire size can plastically change in different social contexts, we hypothesized that the repetition of syllables and syllable sequences could also be context dependent. Here, we used the song of the collared flycatcher as a study system. We recorded the song of focal males under different simulated sociosexual contexts (solo singing, intruder male, approaching female and counter-singing situations in the natural environment), and quantified the context-dependent changes in song structure. As well as the commonly used acoustic variables repertoire size, number of syllables in the song and versatility, we also measured the richness (number of different types) and abundance (number of occurrences) of the repeated syllables and syllable sequences in the song bout recorded in different social contexts. We found lower richness of short repeated sequences and a smaller repertoire size in the context of an approaching female compared to the solo context. Conversely, we found higher richness of long repeated sequences and songs with more syllables in counter-singing compared to the solo context in the song of the focal male. Our study provides evidence that the syllable sequences in the song bout can change depending on the social context in collared flycatchers. Our study also emphasizes the importance of considering the repetition-describing characteristics in addition to the commonly used acoustic characteristics when studying animal acoustic communication.