This study was conducted to characterise macrogeographic variation in the vocalisation of the corncrake Crex crex, a bird species with a non-learned and highly stereotyped call. We also examined: 1) whether call characteristics remained stable across successive breeding seasons within two of the study populations and 2) whether call similarity was related to distance between populations.
Recordings of 352 males from eight populations were analysed. The analyses focused on variation in 1) temporal characteristics (duration of syllables and intervals, duration of the intervals between consecutive maximal amplitude peaks within syllables, called pulse-to-pulse duration (PPD)), and 2) spectral characteristics (minimal and maximal frequency, frequencies below which 25%, 50% and 75% acoustic energy of signal is distributed). We found significant differences in most of the temporal and all of the spectral characteristics between populations. No differences were found in PPD. Significant interannual differences in spectral characteristics were found in both of the populations examined, whereas differences in temporal characteristics were only observed in one population. In general, geographic variation in calls showed clinal distance-dependence, where distant populations showed larger differences in call than neighbouring populations. Our results show that geographic variation in corncrake calls may be very dynamic in the short term and that within-population variation may occur on the same scale as between-population variation. This finding is surprising because call characteristics in non-learners are essentially inherited, and genetic transmission should be very slow. We suggest that the social interactions between males and/or the specific dispersal patterns of this species and the low site fidelity of adult and young birds may be responsible for such pattern.