Craving Ravens: Individual 'haa' Call Rates at Feeding Sites as Cues to Personality and Levels of Fission-Fusion Dynamics?

Raven food calls indicate sender's age and sex

Background

Acoustic parameters of animal signals have been shown to correlate with various phenotypic characteristics of the sender. These acoustic characteristics can be learned and categorized and thus are a basis for perceivers’ recognition abilities. One of the most demanding capacities is individual recognition, achievable only after repeated interactions with the same individual. Still, class-level recognition might be potentially important to perceivers who have not previously encountered callers but can classify unknown individuals according to the already learned categories. Especially for species with high fission-fusion dynamics that repeatedly encounter unknown individuals it may be advantageous to develop class-level recognition. We tested whether frequency-, temporal-, and amplitude-related acoustic parameters of vocalizations emitted by ravens, a species showing high fission-fusion dynamics in non-breeder aggregations, are connected to phenotypic characteristics and thus have the potential for class-level recognition.

Results

The analysis of 418 food calls revealed that some components summarizing acoustic parameters were differentiated by age-classes and sex.

Conclusions

Together, the results provide evidence for the co-variation of vocal characteristics and respective sex and age categories, a prerequisite for class-level recognition in perceivers. Perceivers that are ignorant of the caller’s identity can thus potentially recognize these class-level differences for decision-making processes in feeding contexts.

With whom to dine? Ravens' responses to food-associated calls depend on individual characteristics of the caller

Upon discovering food, common ravens, Corvus corax, produce far-reaching 'haa' calls or yells, which are individually distinct and signal food availability to conspecifics. Here, we investigated whether ravens respond differently to 'haa' calls of known and unknown individuals. In a paired playback design, we tested responses to 'haa' call sequences in a group containing individually marked free-ranging ravens. We simultaneously played call sequences of a male and a female raven in two different locations and varied familiarity (known or unknown to the local group). Ravens responded strongest to dyads containing familiar females, performing more scan flights above and by perching in trees near the respective speaker. Acoustic analysis of the calls used as stimuli showed no sex-, age- or familiarity-specific acoustic cues, but highly significant classification results at the individual level. Taken together, our findings indicate that ravens respond to individual characteristics in 'haa' calls, and choose whom to approach for feeding, i.e. join social allies and avoid dominant conspecifics. This is the first study to investigate responses to 'haa' calls under natural conditions in a wild population containing individually marked ravens.