Long-term variability in the song of the thrush nightingale (Luscinia luscinia) and its relations to the territorial behavior of males

Abstract

Researchers have paid a lot of attention to the temporal variability of birdsong. Data obtained during long-term observations are of particular interest in this context. In this article, we present evidences of the long-term dynamics of the thrush nightingale singing in the Kursk region (Russia) over a period of almost half a century. The average size of individual repertoires remained relatively stable throughout the entire observation period, despite an almost twofold increase in the total size of the population's repertoire. Over 40 years (1975 – 2014), the population repertoire of song types has changed completely. For five years (2014–2018), the repertoire remained relatively stable, while in the next six years (2018–2023) there was a complete change again. Thus, the evolution of the population repertoires of the song types over time includes both periods of relative stability and periods of rapid changes up to a complete change in the composition of the dialect in just a few years. In playback experiments, we tested male response to changes in song over time to ascertain how song evolution has affected signal efficacy in male–male competition. There were no obvious differences in the response of territorial males to the playback of songs recorded in 1975 and 2023. We hypothesize that the perception of thrush nightingales is well adapted to the numerous and relatively rapid changes in the local dialect, so their response to playback does not significantly depend on the specific recording presented.