Can individually characteristic calls be used to identify long-distance movements of Corncrakes Crex crex?

Abstract

Movements of animals at large spatial scales are important in ecology and conservation biology, but current methods for monitoring long-distance movements (e.g. ringing or telemetry) are resource demanding and limit sample sizes. Many birds have individually characteristic calls and songs, and recordings may provide an alternative method for monitoring movements. Previous studies have shown that Corncrake Crex crex night-time calls are individually characteristic. We recorded and analysed Corncrake calls from 60 different territories (30 % of all known territories) in two widely separated areas of Norway in one breeding season to assess the potential of recordings to identify individuals that had moved. Due to extensive mowing of meadows, many territories were used for only a short time, and Corncrakes appeared in new places throughout the breeding season, suggesting movements. By using recordings from the same territory during different nights as a measure of variability within individuals, and recordings from different territories during the same night as a measure of variability between individuals, discriminant analyses indicated that 86 pairwise comparisons of calls from different territories had a high probability (≥0.80) of being from the same bird. Movements could be excluded for 20 of those pairs (23 %) because observations in the two territories overlapped in time. In another 26 cases (30 %), there was overlap in observation dates with other pairs that included the same recording. Thus, chance similarity between different individuals is a problem for individual recognition. Overlap in time decreased with increasing call similarity and, for pairs with very high call similarity (probability ≥0.95), only 5 % overlapped in time. Depending on degree of similarity in calls, the data suggested that 18–48 % of males made movements >10 km, and that the 60 recording sites only represented 31–45 different males. In conclusion, analyses of call recordings suggested that long-distance movements occurred, although positive identification of individual movements is difficult because the likelihood of chance similarity increases with the increasing number of birds recorded.