Australian magpies adjust their alarm calls according to predator distance

Many animals produce antipredator calls in response to the presence of a predator, which, in some species, can provide information about the distance to predator. Although previous research has shown that several bird species are able to encode information about predator distance in their calls, such information is still lacking for a range of species. Moreover, most previous research has categorised the distance between the caller and the predator in two classes (close and far), but subtle acoustic variation can occur within each distance class. We investigate whether calls given by the Western Australian magpie varied according to predator distance. By presenting a taxidermied predator to a population of magpies at different distances, we found that calls varied according to predator distance from the caller, with more calls being produced when the predator was closer. In addition, we found that calls given in response to a predator nearby are acoustically different from those given in response to the same predator further away. This way of encoding information may allow prey to more efficiently moderate antipredator behaviours according to the level of threat.