The ecological and social drivers of cooperation: Experimental field studies in a group-living bird

Helping behavior has evolved across species, varying greatly between individuals. Recent research highlights the importance of social bond strength between actors and recipients, both among and between kin and non-kin, where stronger bonds often increase the likelihood of helping. Exploring this dynamic becomes especially interesting in groups with reproductive and non-reproductive individuals, as it can shed light on the advantages of living in a group. For my dissertation, I investigated the interplay between social bond strength and helping behavior in a wild population of Siberian jays (Perisoreus infaustus) in Northern Sweden. In Chapter 1, I developed a framework to assess social bonds between breeders and non-breeders using measures of aggression and proximity in feeding contexts, evaluating their repeatability and underlying drivers. Chapter 2 explored how social bonds influenced non-breeders’ participation in experimentally elicited intergroup conflicts and whether the participation in such conflicts affected bond strength. In Chapter 3, I investigated the breeders’ helping behavior. Using playbacks of distress calls, I tested whether breeders were more likely to respond to calls from individuals with whom they shared stronger bonds. Overall, my dissertation offers a comprehensive approach to measuring social bonds in Siberian jays, showing that helping responses depend on the context. Contrary to previous assumptions, my results suggest that the role of social bond strength in shaping cooperation in these birds is weaker than thought, supporting the idea of family-living as an intermediate step in the evolutionary transition toward more complex social organization.