Behaviour 2019
The influence of audience and vegetation density on contact calling in a group-living bird
Estelle Meaux, Chao He, Ruchuan He, Aiwu Jiang, Goodale Eben. Guangxi Key Laboratory of Forest Ecology and Conservation, College of Forestry, Guangxi University, Nanning, Guangxi, China

The context-specificity of calls such as alarm calls has been well studied, yet whether repeated calls like contact calls are affected by social or environmental context is less clear. In an aviary study, we found that Swinhoe’s White-eyes have distinct short- and long- distance contact calls, and we analyzed their rate of production in different vegetation densities and group sizes. If contact calls encoded environmental information, we predicted that they would be affected by vegetation density; but if they transmitted social information, rate would vary due to group size and composition. We found that vegetation did not affect the call rate. There was, however, a group-size effect in which solitary birds used more long-distance and fewer short-distance calls than did birds in groups. Further, call rates increased when subjects were in subgroups with affiliated birds, and decreased with birds of different dominance rank. Together, these results show that contact call rate in this species does not encode information about environment, but is socially-specific, and we suggest this can offer information about the social relationships between signaler and receiver to eavesdroppers.