Cooperative bird discriminates between individuals based purely on their aerial alarm calls

From an evolutionary perspective, the ability to recognize individuals provides great selective advantages, such as avoiding inbreeding depression during breeding. Whilst the capacity to recognize individuals for these types of benefits is well established in social contexts, why this recognition might arise in a potentially deadly alarm-calling context following predator encounters is less obvious. For example, in most avian systems, alarm signals directed toward aerial predators represent higher predation risk and vulnerability than when individuals vocalize toward a terrestrial-based predator. Although selection should favor simple, more effective alarm calls to these dangerous aerial predators, the potential of these signals to nonetheless encode additional information such as caller identity has not received a great deal of attention. We tested for individual discrimination capacity in the aerial alarm vocalizations of the noisy miner (Manorina melanocephala), a highly social honeyeater that has been previously shown to be able to discriminate between the terrestrial alarm signals of individuals. Utilizing habituation-discrimination paradigm testing, we found conclusive evidence of individual discrimination in the aerial alarm calls of noisy miners, which was surprisingly of similar efficiency to their ability to discriminate between less urgent terrestrial alarm signals. Although the mechanism(s) driving this behavior is currently unclear, it most likely occurs as a result of selection favoring individualism among other social calls in the repertoire of this cooperative species. This raises the intriguing possibility that individualistic signatures in vocalizations of social animals might be more widespread than currently appreciated, opening new areas of bioacoustics research. Lay Summary: At least for the Australian noisy miner bird, "What is in a name?" is not as important as "what is in a call?" In miners, individual birds discriminate between one another based upon the vocal characteristics of their short aerial alarm calls. This ability was unexpected, as the costs of not responding to the presence of a highly dangerous, potential predator that these calls are directed toward were proposed to outweigh the benefits of differentiating between callers of different identities. Additional study is required to understand why miners have been selected to be able to achieve this discrimination, but one likely possibility is that this ability may be the by-product of inherent differences in different bird's "voices" that are generated by random morphological variance.