Microgeographic call variation in a non-learning species, the Corncrake (Crex crex)

Microgeographic variation in bird song has been studied in many species. However, it remains to be more fully described in birds that do not learn song and that thus have largely innate vocalisations. In this study, we focused on microgeographic variation in the territorial calls of one such non-learning species, the Corncrake (Crex crex). We examined the temporal and spectral characteristics of male Corncrake calls recorded in five separate populations in Poland. We found significant but weak relationships between some of the call characteristics and between-caller distances in four populations. The patterns observed were inconsistent. For some call characteristics, similarity decreased as distance between callers increased, while the opposite was true for other characteristics. Moreover, the same call characteristics showed opposite patterns in different populations or even within the same population but in different years. These findings suggest that the specific spatial distribution of the different quality habitats in which populations are located may have a crucial influence on microgeographic variation in calls. Alternatively, in non-learning species, various levels of microgeographic variation in calls might arise independently as a consequence of (1) social interactions among males, during which birds modify some parameters of their inherited call; or (2) territory occupancy patterns that minimize or maximize call similarity among neighbours.