Unravelling effects of fine-scale changes within wild-bird flocks on sociality

Abstract

O_LISocial structure and individual sociality impact a wide variety of behavioural and ecological processes. Although it is well known that changes in the physical and social environment shape sociality, how perturbations govern sociality at a fine spatial scale remains poorly understood. By applying automated experimental treatments to RFID-tracked wild great tits (Parus major) in a field experiment, we examined how individual social network metrics changed when food resources and social stability were experimentally manipulated at the within-group spatial scale. C_LIO_LIFirst, we examined how individual sociality responds when food resources changed from a dispersed distribution (50m apart) to a clustered distribution (1m apart). Second, we tested how sociality changed when individuals were restricted to feeding in a manner that mimics assortative behaviour within flocks. Third, we tested the effects of experimentally manipulating the stability of these social groupings. Finally, we returned the feeders to the original dispersed distribution to test whether effects carried over. C_LIO_LIRepeatability analyses showed consistent differences among individuals in their social phenotypes across the various manipulations; dyadic association preferences also showed consistency. Nevertheless, average flock size and social centrality measures increased after the food was clustered. Some of these metrics changed further when birds were then forced to feed from only one of the five clustered feeders. There was some support for group stability at individual feeders also impacting individual social network metrics: increase in flock size was more pronounced in the stable than the unstable group. Most of the differences in sociality were maintained when the food distribution returned to the dispersed pattern, and this was caused primarily by the change in resource distribution rather than the social manipulation. C_LIO_LIOur results show that perturbations in the access to resources and social group stability can change sociality at a surprisingly fine spatial scale. These small-scale changes could arise through a variety of mechanisms, including assortative positioning within groups due to, for instance, similarity among individuals in their preferences for different resource patches. Our results suggest that small-scale effects could lead to social processes at larger scales and yet are typically overlooked in social groups. C_LI