Geographic Variation in Note Types of Alarm Calls in Japanese Tits (Parus minor)

SIMPLE SUMMARY: Divergence in acoustic signal systems might play a central role in speciation. Alarm calls are part of the acoustic signal system, which can transmit information about impending threats to group members and relatives. This study focuses on geographic variation in the note types of alarm calls in Japanese tits, a small songbird species distributed broadly in China. It was found that the note types of the same population responding to different intruders were roughly the same, and that all the three populations had shared note types and their own unique note types to warn about the same intruder. Moreover, we found large differences in the acoustic parameters of shared common note types among populations. These findings provide valuable information to improve the collective understanding of the evolutionary mechanisms of alarm call systems in birds. ABSTRACT: Geographic variability in acoustic signals has been documented in many bird species. However, geographic variations in alarm calls have been so far neglected despite their crucial role on reducing risk to group members and relatives. We analyzed the note types and acoustic parameters of Japanese tit (Parus minor) alarm calls to three types of intruders (a nest predator, an adult predator, and a harmless species) from three populations in China. Our results revealed that tits in the same population produce similar note types to different intruders, but the three populations only shared six note types and each population had unique note types. The frequency and duration parameters of three shared common note types were significantly different among populations. The three populations belong to the same species, thus they have shared note types. We suspect that the unique note types occurring in each population may be related to three potential reasons: founder effect, predation pressure, and vocal learning. The differences in acoustic parameters of common notes among populations may be a consequence of adaptations to their environments. We suggest that population differences in the note levels of bird alarm calls do exist.