Fission-fusion dynamics and social cognition in wild ravens

Studies on children and smart non-human animals like primates indicate a link between complexity in social life and the development of intelligence. A key aspect of complexity is the formation of social relationships like dominance, friendship and partnership. It likely becomes more and more difficult to keep track of such relationships when groups increase in size or when individuals vary in spatial cohesion and group membership over time, i.e. they show a high degree of fission-fusion dynamics. Until recently, little attention has been paid to such dynamics, even though highly stable groups are the exception rather than the rule in many social systems outside primates. Hence, the interplay between fission-fusion dynamics, social relationships and cognition is still little understood. Recent research has shown that ravens Corvus corax combine features of both, high social complexity and high fission-fusion dynamics. Raven non-breeders form groups that are structured by different types of social relationships, creating a system of dependent ranks and alliances. Yet, these groups are also characterized by high individual variation in fission-fusion dynamics, with some birds staying at a foraging site over long time periods and others for a few days only. The aim of this project is to investigate i) what causes the pronounced individual differences in fission-fusion dynamics of raven non-breeders and ii) how do these differences in dynamics affect the birds knowledge about relationships. Specifically, we will test the hypotheses that i) social integration is a main determinant of whether or not individuals stay with a particular group at a given location and that ii) those ravens that tend to stay develop personalized knowledge about their fellow local group members, whereas those ravens that tend to wander around may use rules of thumb in social interactions with local birds. The proposed research will be conducted on our unique study population of wild ravens in the Austrian Alps, out of which >300 individuals are marked. It will feature state-of-the-art methods of tracking birds and analysing their social networks, combined with experimental manipulation of the temporal group composition and individual tests concerning stress coping and social knowledge. The integrative aspect of the proposed project promises important new perspectives for understanding the development of social profiles and decision-making under conditions of social stability and instability. The focus on fission-fusion dynamics will improve our understanding of socio-cognitive evolution in general.

Complexity in social life has been suggested as one of the main driving forces for the development of higher cognitive abilities in humans and non-human animals. A key aspect of complexity is the formation of social relationships, which become difficult to keep track of when groups increase in size or when individuals vary in spatial cohesion and group membership over time, i.e. they show a high degree of fission-fusion dynamics. Until recently, little attention has been paid to such dynamics, even though highly stable groups are the exception rather than the rule in many social systems outside primates. Hence, the interplay between fission-fusion dynamics, social relationships and cognition is still little understood. Common ravens combine features of both, high social complexity and high fission-fusion dynamics. Raven non-breeders form groups that are structured by different types of social relationships, creating a system of dependent ranks and alliances. Yet, these groups are also characterized by high inter-individual variation in fission-fusion dynamics, with some birds staying at a foraging site over long time periods and others for a few days only. The aim of this project was to investigate i) the pronounced individual differences in fission-fusion dynamics of raven non-breeders and ii) how these differences in dynamics affect the birds' foraging skills and knowledge about relationships. We conducted behavioral studies and acoustical playback experiments on our unique study population of wild ravens in the Austrian Alps, out of which >400 birds are marked individually and >80 birds got tagged with GPS loggers for tracking their movements. While our behavioral observations confirmed a high and consistent interindividual variation in using foraging sites, we could find hardly any effects of these differences on the ravens' foraging skills (showing/avoiding kleptoparasitism, food caching); we did, however, find effects on their vocal behavior, with locals ravens being more active than vagrants, and ravens generally paying much attention to the callers' identity, age and/or social class. The latter was confirmed with playback studies under controlled conditions on temporarily captive ravens. These findings suggest that ravens are capable of telling group members apart. What remains still unclear is how much the fission-fusion dynamics affect the ravens' personal knowledge about group members, as we could not find the predicted link between the birds' responses to playback and their degree of fission-fusion dynamics so far. Future studies will reveal whether our results were constrained by methodological or analytical short-comings or whether ravens could potentially handle much more social information as originally thought. The project thus laid the basis for exciting further work. Notably, it kick-started a long-term monitoring of GPS-tagged ravens at our study site in the Alps and a similar project in Yellowstone National Park.