Sounding the alarm: Functionally referential signaling in Azure-winged Magpie

Functionally referential signals are a complex form of communication that conveys information about the external environment. Such signals have been found in a range of mammal and bird species and have helped us understand the complexities of animal communication. Corvids are well known for their extraordinary cognitive abilities, but relatively little attention has been paid to their vocal function. Here, we investigated the functionally referential signals of a cooperatively breeding corvid species, Azure-winged Magpie (Cyanopica cyanus). Through field observations, we suggest that Azure-winged Magpie uses referential alarm calls to distinguish two types of threats: ‘rasp’ calls for terrestrial threats and ‘chatter’ calls for aerial threats. A playback experiment revealed that Azure-winged Magpies responded to the two call types with qualitatively different behaviors. They sought cover by flying into the bushes in response to the ‘chatter’ calls, and flew to or stayed at higher positions in response to ‘rasp’ calls, displaying a shorter response time to ‘chatter’ calls. Significant differences in acoustic structure were found between the two types of calls. Given the extensive cognitive abilities of corvids and the fact that referential signals were once thought to be unique to primates, these findings are important for expanding our understanding of social communication and language evolution.