Within-season decline in call consistency of individual male Common Cuckoos (Cuculus canorus)

Abstract

Numerous studies have identified individually distinctive vocal characteristics and call consistency in different bird species. If these vocal characteristics are to be utilised as non-invasive markers for monitoring purposes, then they must remain stable over time. Three recent studies have shown that it is possible to identify individual male Common Cuckoos (Cuculus canorus) based on vocal characteristics, but whether these characteristics are stable over the duration of a breeding season remains unknown. We recorded 1032 syllables from 30 male Common Cuckoos in a Northeast Asian population. We banded six of these males and made repeated recordings of their cu-coo advertisement call across a 19-day period of the breeding season in China. We used three methods to identify individuals: discriminant function analyses (DFA), correlation analysis (CA) and spectrographic cross-correlation (SPCC). We also used repeatability analysis to test whether call consistency (the number of syllables in each calling bout) was repeatable within individuals. Based on the same-day recordings, calls from the same male were more similar in their characteristics than compared to those of different males, and yielded correct rates of classifying individuals of 93.6% (SPCC), 90.8% (DFA), and 71.5% (CA). However, these rates declined to 40.5% (SPCC), 40.7% (DFA) and 27% (CA) when using recordings over the 19-day period. Call consistency was repeatable within individuals across two successive calling bouts, but this individual repeatability disappeared when several (more than two) calling bouts from the same day or bouts from the different days of the study were included in the analyses. Declines in the correct rate of identifying individual male cuckoos and call consistency in this study raise concerns that individual male cuckoo calls may be more variable than previously thought.