Know your place - Social network analysis in cooperatively breeding white-winged choughs (Corcorax melanorhamphos)

Abstract

Cooperative breeding is a specialised type of social system in which individuals work together as a group to raise young. This breeding system entails variable costs and benefits for individuals based on their position in group social structure. Social network analysis has become an important tool for understanding causes and consequences of individual positions in such social structures. In this thesis I used social network analysis to understand the impact of individual attributes and behaviours on the social position of group members of an obligate cooperatively breeding bird, the white-winged chough (Corcorax melanorhamphos). I studied five cooperative groups of choughs in the Canberra area and constructed networks from spatial association data to give values for two group-level and three individual-level social network measures. The two group-level social network measures were the extent of their assortative behaviour based on their traits (assortativity) and social cohesion (density). The three individual-level social network measures were number and strength of direct associations (weighted degree), distance to all other individuals in the group (closeness centrality) and network connectedness (eigenvector centrality). I also identified social clusters. I then compared social networks between two stages of breeding, the nesting and post-fledging stages, to understand the impact of nesting activity on social structure. My results confirmed the validity of using networks derived from spatial associations in choughs to quantify social structure and changes in structure. The networks showed that choughs do not assort by age, likely due to poor foraging skills in immature choughs. Choughs assorted by sex but not by breeding status, possibly reflecting differences in mating strategies. Individual traits that impacted a chough’s direct associations might reflect mating strategies, demographics and resource availability. Group size had a significant impact on social measures, suggesting a need for selectivity in choices of social partners due to fewer opportunities to socialise. I suggest that the maintenance of networks between the two breeding stages was a result of choughs compensating for the cost of time investment on their key relationships from nest sitting. Changes in individual network position between breeding stages correlate to contributions to care of young, providing support for the social prestige hypothesis.