Cultural conformity and persistence in the context of differing site fidelity

Animal culture often shows geographic structure, with nearby individuals sharing more cultural features than individuals further apart. However, spatial extent of cultural features, along with the degree of conformity to local cultures, vary within and among species. Further, rates of cultural change presumably also vary, though documentation of temporal variability lags behind documentation of spatial variability, and mechanisms driving this variation have not been sufficiently explored. We hypothesized that conformity to local culture in Oscine songbirds and the persistence of culture over time and space are promoted by habitats that facilitate stable populations in which individuals show relatively high site fidelity. In contrast, sites in which habitat features cause rapid population turnover provide more vacant territories and so more opportunities for colonization. Colonization should drive more rapid cultural change, either through adult colonists importing foreign cultural variants or young colonists making errors as they learn the local song. To test these hypotheses, we examined temporal and spatial variation in vocal culture in a songbird (dickcissel, Spiza americana) in two distinct habitats. As predicted, we found high average site fidelity in relatively stable native grasslands and much lower average site fidelity in nearby cropland sites which were disturbed by farming practices during the breeding season. We also found higher levels of average song similarity and slower average changes in vocal culture in our grasslands relative to croplands, though we found no evidence of different spatial scales of song similarity between these habitats. Although our conclusions are based on many recorded songs, automated assessments of song similarity underestimated the overall degree of song similarity. Thus we may have also underestimated the strength of the effects of time and distance on song similarity. Despite these shortcomings, our results call attention to the understudied but potentially important role of demographic factors influencing cultural evolution.