Early-life social instability affects aggression, but not response inhibition, in chickens

Living in complex social environments presents behavioural and cognitive challenges. A key challenge is the regulation of aggression, which may be facilitated by response inhibition, the ability to suppress inappropriate actions. In more complex social environments, greater variability in interactions may increase demands for aggression regulation, promoting the development of response inhibition. However, social instability, a form of complexity characterised by frequent changes in group composition, can elevate aggression and may instead impair inhibition. To test these competing predictions, we raised 144 chickens (Gallus gallus domesticus) in either stable or unstable social groups for five weeks. We observed the aggression within their enclosures following the final manipulation and assessed their response inhibition using a thwarting task and a cylinder task. Unstable groups initially showed more aggression than stable groups following regrouping, but this declined rapidly to the same lower level of aggression as the stable groups. Contrary to our predictions, there were no differences between birds raised in stable and unstable groups for any measure of response inhibition, and individual variation in aggression did not correlate with inhibitory performance. These findings suggest that social instability influences aggression but does not affect the development of response inhibition in chickens, highlighting the potential context- and species-specific nature of social effects on cognition.