Animals in natural communities gain information from members of other species facing similar ecological challenges [1-5], including many vertebrates that recognize the alarm calls of heterospecifics vulnerable to the same predators [6]. Learning is critical in explaining this widespread recognition [7-13], but there has been no test of the role of social learning in alarm-call recognition, despite the fact that it is predicted to be important in this context [14, 15]. We show experimentally that wild superb fairy-wrens, Malurus cyaneus, learn socially to recognize new alarm calls and can do so through the previously undemonstrated mechanism of acoustic-acoustic association of unfamiliar with known alarm calls. Birds were trained in the absence of any predator by broadcasting unfamiliar sounds, to which they did not originally flee, in combination with a chorus of conspecific and heterospecific aerial alarm calls (typically given to hawks in flight). The fairy-wrens responded to the new sounds after training, usually by fleeing to cover, and responded equally as strongly in repeated tests over a week. Control playbacks showed that the response was not due simply to greater wariness. Fairy-wrens therefore learnt to associate new calls with known alarm calls, without having to see the callers or a predator. This acoustic-acoustic association mechanism of social learning could result in the rapid spread of alarm-call recognition in natural communities, even when callers or predators are difficult to observe. Moreover, this mechanism offers potential for use in conservation by enhancing training of captive-bred individuals before release into the wild.

A growing number of studies have shown that vocal mimicry appears to be adaptive for some bird species, although the exact function of this behaviour varies among species. Previous work has looked at the function of the vocal mimicry of non-alarm sounds by the Greater Racket-tailed Drongo (Dicurus paradiseus). But drongos also imitate sounds associated with danger, such as predators' vocalisations or the mobbing-specific vocalisations of other prey species, raising the question of whether the function of mimicry can vary even within a species. In a playback experiment, we compared the effect on other species of different drongo vocalisations including: (1) predator mimicry, (2) mobbing mimicry, (3) drongo species-specific alarms, (4) drongo species-specific non-alarms and (5) a control (barbet) sound. Both mobbing mimicry and drongo species-specific alarms elicited flee responses from the most numerous species in the flocks, the Orange-billed Babbler (Turdoides rufescens). Mobbing mimicry also elicited mobbing responses from the Orange-billed Babbler and from another gregarious babbler, the Ashy-headed Laughingthrush (Garrulax cinereifrons); when responses from both species were considered together, they were elicited at a significantly higher level by mobbing mimicry than by the barbet control, and a level that tended to be higher (0.07 < p < 0.10) than the response to drongo-specific alarms. Predator mimicry elicited flee and mobbing responses at an intermediary level. Our results support the hypotheses that mobbing mimicry is a specific category of mimicry that helps attract the aid of heterospecifics during mobbing and that alarm mimicry can in some cases be beneficial to the caller.Ethology 120 (2014) 266-274

Social information varies in its reliability and relevance, requiring individuals to use rules to avoid inappropriate responses to false information. A simple rule is only to respond when a certain number of individuals provides similar information. Although individuals within social groups can use such numerical rules to assess conspecific information and make consensus decisions, it is unknown whether individuals apply similar rules when assessing the value of heterospecific information. We consider the case of individuals eavesdropping on heterospecific alarm calls. Eavesdroppers may be particularly vulnerable to false alarms because of the large pool of potential callers and variability in the specific threats to which they call. Individuals might therefore value alarm calls more if they come from multiple callers or multiple species than from a single caller or a single species. We tested these predictions using field playback experiments on wild Australian magpies (Gymnorhina tibicen). Magpies responded more strongly to alarm calls coming from two callers versus one caller of the same heterospecific species. However, in contrast to our prediction, magpies responded similarly to alarm calls from two individuals of different species as they did to alarm calls from two individuals of the same species. We conclude that the number of calling individuals does affect response, probably because information from multiple callers is more reliable, but that the value or reliability of information from multiple species may depend on the types of alarm calls and combination of species involved.

Information about predators can mean the difference between life and death, but prey face the challenge of integrating personal information about predators with social information from the alarm calls of others. This challenge might even affect the structure of interspecific information networks: species vary in response to alarm calls, potentially because different foraging ecologies constrain the acquisition of personal information. However, the hypothesis that constrained personal information explains a greater response to alarm calls has not been experimentally tested. We used a within-species test to compare the antipredator responses of New Holland honeyeaters, Phylidonyris novaehollandiae, during contrasting foraging behaviour. Compared with perched birds, which hawk for insects and have a broad view, those foraging on flowers were slower to spot gliding model predators, showing that foraging behaviour can affect predator detection. Furthermore, nectar-foraging birds were more likely to flee to alarm call playbacks. Birds also assessed social information relevance: more distant calls, and those from another species, prompted fewer flights and slower reaction times. Overall, birds made flexible decisions about danger by integrating personal and social information, while weighing information relevance. These findings support the idea that a strategic balance of personal and social information could affect community function.

Several species of birds vocally imitate sounds associated with danger. Two anecdotal studies suggest that such ‘danger mimicry’ increases during nesting, but such a relationship has not been quantitatively demonstrated. Sri Lanka drongos (Dicrurus paradiseus lophorhinus) are known to imitate predators and other species’ mobbing and alarm calls in alarm contexts. Here we investigated whether drongos vary their production of danger mimicry in different nesting stages (building, incubation, nests with hatchlings, fledglings still outside of mixed-species flocks), and when foraging away from young in mixed-species flocks. We recorded drongos over two breeding seasons at 14 different nesting trees, used year-after-year. We found that of all the types of danger mimicry, imitation of predators was the most common and exclusive to drongos that had young offspring. Such predator mimicry was observed at a higher rate during the hatchling and fledgling stages compared to incubation or flocks. Danger mimicry did not, however, increase during this stage in isolation: drongo species-specific alarm calls also increased, and the close connection between these two types of calls did not appear to change. Although it is possible that the association between danger mimicry and species-specific alarm calls could help young birds learn sounds associated with danger, the performance of this behaviour does not seem exclusive enough to interactions between adult drongos and their offspring to meet functional definitions of teaching.