Immigration and dispersal are key determinants of cultural diversity in a songbird population

Socially learned signals and behaviors are found throughout the animal kingdom and often show striking variation within species over space and time. However, the extent to which this cultural diversity is generated by demographic factors such as immigration and dispersal has proved difficult to investigate and remains largely untested in a natural setting. Focusing on 14 different local neighborhoods within a wild population of great tits Parus major, we examined the relationship between individual movements over a 7-year period and patterns of cultural diversity at a neighborhood level, assessed using 2 indices: Song repertoire size and repertoire novelty, measured at the neighborhood (but not individual) level. We found that the repertoire size of a neighborhood is positively correlated with its levels of immigration, but that repertoire novelty is constrained by dispersal and geographic proximity among neighborhoods, both of which promote song sharing. In parallel, we show that the acoustic structure of some songs changes subtly over distance, in line with the view that learning errors can lead to the establishment of novel social traits (cultural differentiation). Our findings demonstrate that spatial variation in cultural diversity in animal societies can partly be explained as the outcome of dispersal and immigration transferring traits between neighborhoods and also suggest that trait transmission declines in fidelity over distance.