Song type sharing in common nightingales, Luscinia megarhynchos, and its implications for cultural evolution

The sharing of song types between males of the same local population is a common phenomenon in some songbird species. One presumed advantage of such sharing is that it enables ‘song matching’ (i.e. responding to an interactant with the song he just sang or another song of the interactant’s repertoire). Song sharing probably arises through song learning, whereby males of some species prefer acquiring songs shared in the local population. However, such a preference may lead to uniformity of repertoires, devaluating the signal value of shared songs. Here we investigated repertoire composition in a local population of nightingales. More precisely, we analysed the number of song types shared by a given number of males and compared the finding with different simulated models of song acquisition. We found that proportions of both (songs shared by many males as well as songs sung by a single male only) were clearly more common than expected. We also simulated the cultural evolution of the population’s repertoire. The results of these simulations supported our conclusion from the simulation of song acquisition that unshared songs arise through invention of novel song types or modification of existing ones, although we cannot rule out that unshared songs also appear through immigration of males. Our findings suggest that nightingales have a preference to acquire both shared song types, which enable matching the songs of opponents, and unshared or ‘invented’ new song types, which may help to avoid being matched by opponents.