The vocal repertoire of the cooperatively breeding Apostlebird (Struthidea cinerea)

The role of acoustic communication in facilitating social interactions and mediating cooperative behaviour has been highlighted by many studies. In the 'social complexity hypothesis' of communication, many more specialised signals are likely to evolve in social species where many individuals interact in multiple behaviours. However, before the function of vocalisations in these systems can be elucidated accurately, the characteristics and social context of each vocalisation must be determined. Apostlebirds (Struthidea cinerea) are a highly vocal and social species with an obligate cooperatively breeding life-history. In this study, we describe the environmental and behavioural context of the 17 most common calls from the vocal repertoire of a study population of Apostlebirds in north-western New South Wales. The vocalisations given by individuals ranged from simple, monosyllabic calls through to more complex calls with multiple syllables and frequency modulations. All these calls were broadly categorised as close-range, long-range, alarm context, or associated with nesting. Most call-types were given by both sexes, and by both breeders and helpers, including alarm calls that were given by both juveniles and adults. In contrast, calls given during inter-group interactions were predominantly by adults.