The causes and consequences of individual variation in inhibitory control in the North Island robin (Petroica longipes)

Inhibitory control is a crucial component of goal-directed behaviour, allowing animals to suppress prepotent responses and ignore outdated information. Despite increasing interest in the evolution of this cognitive ability, the heritability and fitness consequences of intraspecific variation in inhibitory control in the wild are largely unknown. In addition, identifying fitness-linked behaviours underpinned by inhibitory control is key to understanding not just whether, but how this ability evolves. This thesis explores the causes and consequences of individual differences in inhibitory control in wild North Island robins (Petroica longipes), referred to hereafter by their Māori name, toutouwai. This endemic New Zealand passerine engages in two behaviours that have been hypothesised to require the inhibition of prepotent responses: caching and food-sharing.

In my first data chapter, I quantified individual differences in inhibitory control using detour and reversal learning tasks. Individual performances showed no convergent validity across the two tasks, but within-task performance was robust to non-cognitive confounds and showed long-term repeatability. This suggests that detour and reversal learning tasks reliably measure consistent individual variation in independent components of inhibitory control in toutouwai. Yet inhibitory control appears to be largely plastic in this species, as there was no evidence that task performance was heritable. In my second data chapter, I explored whether toutouwai are capable of self-control, an ability related to inhibitory control that allows animals to resist instant gratification and obtain better-quality outcomes that are more effortful and/or delayed. Individuals varied in their ability to resist an immediate, low-quality reward in favour of travelling to a better-quality alternative. This experiment demonstrated for the first time that a wild bird is capable of self-control. However, while this task was a valid self-control measure at a group level, individual-level performance was confounded by food preferences and the satiation and/or learning effects associated with increasing trial number. Self-control performance was also unrelated to detour task performance, suggesting that the choice component in self-control tasks distinguishes this ability from the pure inhibition of prepotent motor responses. In my third data chapter, I investigated the behavioural and fitness correlates of inhibitory control. Individual toutouwai of both sexes consistently differed in their propensity to cache food, and males consistently differed in their propensity to share food with their partners during courtship. However, these differences were not predicted by their inhibitory control. Likewise, there was no relationship between inhibitory control and annual or lifetime reproductive success.

This thesis is the most detailed investigation to date into the behavioural functions and evolutionary potential of inhibitory control in the wild. My findings suggest that inhibitory control is not currently under directional selection in this toutouwai population. This supports the possibility that directional selection for broadly used cognitive traits like executive functions may be uncommon, potentially because these traits underpin a range of behaviours with differing relationships to fitness. Nonetheless, my research provides valuable insight into how inhibitory control and self-control can be robustly measured in wild animals, enabling future researchers to better address fundamental questions about the evolution of these abilities.