Social and spatial drivers of the multitiered structure of zebra finch social networks.

Social network structure plays a key role in shaping processes in animal populations. However, our understanding of how individual-level social decisions scale up to population-level social structures remains limited, particularly outside mammals. Here, we used continuous, fine-scale tracking of four large captive colonies of zebra finches (Taeniopygia guttata), revealing that zebra finches consistently maintain 1-2 closest contacts, 6-7 close contacts and 22-24 intermediate contacts, with the identities of these contacts remaining stable across days. By separating spatial co-occurrence from social preferences using null models, we demonstrate that closest and close partners are maintained by social choice, while intermediate partners are shaped by spatial affinity. These results suggest that zebra finch egocentric networks are made up of at least three different tiers of consistent, differentiated relationships. Importantly, we show that these tiers-when combined across individuals-form a multitiered social structure at the colony level. Finally, we review literature on egocentric animal networks, highlighting similarities in patterns to other species, and discuss the distinctions between multitiered and multilevel societies. Our results suggest that fundamental constraints in time, cognition and spatial organization may drive common structural properties in animal social networks across taxa.