Who wants food? Individual characteristics in raven yells

Discriminating between different individuals is considered as prerequisite for any forms of social knowledge. In birds, discriminating between conspecifics based on individual characteristics has been tested mainly in the auditory domain with territorial calls and songs for neighbour and kin discrimination but little is known about discriminating between signallers in food calls. Ravens utilize a large set of calls and show individually distinctive call repertoires. Moreover, they show advanced social tactics during foraging, suggesting that they are capable of dealing with conspecifics on an individual basis. When confronted with food that is difficult to access, ravens produce particular calls ('haa', yells); these calls attract other ravens and, thus, have been hypothesized to serve as 'functionally referential signals'. We here examined whether ravens are able to differentiate between individuals on the basis of these food calls. We first analysed individual differences in call parameters, using 424 food calls recorded from 18 individually marked wild ravens in the Austrian Alps. We then tested 18 captive ravens for recognition of individual differences in food calls with playbacks, using a habituation-dishabituation design. We found evidence that food calls show individual call characteristics in fundamental frequency and intensity-related measurements providing ravens with the opportunity to respond according to these individually distinct features. Furthermore, ravens discriminated between unfamiliar ravens in the habituation-dishabituation experiment, indicating that they may discern individual differences. Our results suggest that raven food calls are individually distinct and that the birds may be capable of differentiating between food-calling individuals.