Function of note strings in Japanese Tit alarm calls to the Common Cuckoo: a playback experiment

摘要

Background: Birds produce alarm calls to convey information about threats. Some Passerine alarm calls consist of several note strings, but few studies have examined their function. Previous studies have shown that Japanese Tits (Parus minor) can alter the calling rate and number and combination of notes in response to predators. We previously found the combinations of note types in Japanese Tit alarm calls to be significantly different in response to the Spar-rowhawk (Accipiter nisus) and Common Cuckoo (Cuculus canorus). Methods: Through playback experiments, we tested whether the note strings in Japanese Tit alarm calls to the Com-mon Cuckoo have different functions in conveying information. The note strings of selected alarm calls were divided into the categories of C and D, and different calls were then constructed separately based on the two note string categories. Original alarm calls (C–D), C calls and D calls were played back to male Japanese Tits during the incubation period. Results: Male Japanese Tits had a significantly stronger response to C calls than to C–D calls, and they showed a significantly stronger response to both C and C–D calls than to D calls, suggesting that Japanese Tits discriminated between the C and D calls. Conclusions: Our study demonstrated that the C- and D-category note strings of Japanese Tit alarm calls to the Common Cuckoo have different functions, which supports the previous finding that different note strings in an alarm call can provide different information to receivers. However, the exact meanings of these note strings are not yet known, and further investigation is therefore required.