Birds Learn Socially to Recognize Heterospecific Alarm Calls by Acoustic Association

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. Animals often learn to eavesdrop on alarm calls of other species, but the mechanisms are unclear. Potvin et al. show that a wild bird species learns socially to recognize new calls by associating unfamiliar sounds with known alarm calls without needing to see a predator. Such acoustic-acoustic association may lead to rapid spread of recognition.