Individuality obscures geographical song variation in two passerine sister species with contrasting distributions and movement ecology

Songbirds are a well‐established model group for the study of cultural evolution as their songs are learned (i.e. culturally transmitted), which may lead to divergence in song characteristics between populations. Song variation across populations may be affected by geographical isolation, timing and duration of the learning period, and life strategies such as migratory behaviour. In this study, we explored geographical song variation in two congeneric sister species of songbirds with a simple song: the Palaearctic migrant Tawny Pipit Anthus campestris , and the sedentary Berthelot's Pipit Anthus berthelotii , endemic to Macaronesian archipelagos. We recorded songs of territorial males from six Tawny Pipit populations on the European mainland, and of Berthelot's Pipits on three Canary and two Madeiran islands. We confirmed that both species have individually unique repertoires, usually consisting of a single song type per male. The structural characteristics of song types within each species were compared by dynamic time warping analysis. In addition, we quantified several temporal and frequency measures to characterize geographical patterns of song dissimilarity. These were remarkably similar between species, despite differences in their natural history. In both species, we observed very high within‐population variation of song types, possibly reflecting rapid cultural evolution of song driven by the constant introduction of novel, although minor, individual‐specific differences. Mean song dissimilarity was higher when song types were compared between different regions (mainland localities or islands) than within them. However, only Berthelot's Pipits showed significant differences in geographical song variation at the smallest and largest spatial scales, which might reflect the sedentary behaviour of this species and the isolation of Macaronesian archipelagos, respectively. Nevertheless, and contrary to our expectations, the divergence in song observed at even the largest spatial scales was not sufficient in either species to infer the country or archipelago of origin of individual birds. The congruent patterns between the two species indicate that, in songbirds with individually unique song types, cultural evolution may promote high local diversity, largely obscuring geographical differentiation at broader spatial scales.