Do the rain calls of Chaffinches indicate rain?

Abstract

AbstractFor more than 300 years, the rain call of the Common Chaffinch (Fringilla coelebs) has been thought to herald rain—hence the name. However, the biological function of this vocalisation still remains unknown. Because rain calls are produced only by males during the breeding season, it has been suggested that the call serves a territorial function and that it may replace song in adverse situations, such as bad weather. However, it is unclear whether rain calls are linked to precipitation at all. Here, we explored the relationship between the occurrence of rain calls and the weather, based on the hypothesis that rain calls are produced instead of song during rainfall. For that purpose, we conducted three studies on different geographical and temporal scales: a large-scale analysis across Europe (relating 242 audio recordings from the Xeno-Canto archive to weather data) and two observational studies in Germany (one cross-sectional study surveying 509 Chaffinches and one longitudinal study on 49 selected males over a period of two weeks). We found no association between rain calls and rainfall in any of the three datasets (but males tended to produce more rain calls with increasing cloud cover and wind force). However, the occurrence of rain calls varied markedly with the social context, as males were more likely to rain–call in the presence of a female, suggesting a function within the pair bond. Overall, we press for more studies on bird calls, and the rain call (although inappropriately named) appears to be a particularly interesting candidate.