Effects of fine-scale changes in resource access and social stability on the sociality of foraging flocks of wild birds

Social structure arises from individual behaviours and can impact a wide variety of behavioural and ecological processes. Although changes in the physical and social environment shape sociality, how perturbations govern sociality at a fine spatial scale remains poorly understood in wild populations. By applying automated experimental treatments to radio frequency identification tracked wild great tits, Parus major, in a field experiment, we examined changes in individual social network metrics in response to manipulated changes in two factors: (1) the distribution of food resources; and (2) the stability of the composition of individuals that had access to the same feeders, a subtreatment that was applied during one of the resource treatment levels. Repeatability analyses revealed consistent differences among individuals in their social network metrics at feeders across the various treatments. As expected, the average flock size and social network metrics increased when the distribution of food changed from two single feeders spaced 50 m apart (dispersed) to one location with an array of five feeders 1 m apart (clustered). However, some social network metrics changed further when individuals were restricted to feeding from only one of the five clustered feeders, even though all five feeders remained active. We also show how experimentally imposed group membership stability can impact social network metrics. Most changes in social network metrics were maintained when the food distribution returned to the dispersed pattern with two feeders 50 m apart, although dyadic associations between individuals of known identity were largely maintained. Our results show that perturbations in access to resources and social group stability at a surprisingly fine spatial scale can change connections in social networks during foraging. Fine-scale effects can arise through assortative positioning within groups and can have important consequences for social processes at larger scales, yet are typically overlooked.