Sexual conflict over parental investment in offspring occurs in species with biparental care due to the shared benefits but individual costs of care, such that the optimum level of investment for an individual is less than that of its partner. Sexual conflict can result in costs for offspring, but a recent theoretical model suggests that parents might reduce such costs via conditional cooperation in the form of turn-taking (alternation) during
provisioning. Various empirical studies have found evidence supporting this model. In addition, provisioning synchrony is thought to be related to alternation, perhaps facilitating alternation by enabling partner monitoring. Whether these behaviours are adaptive is not yet fully understood, with studies calling for more research into the fitness consequences of these behaviours. As a result, this thesis explored potential costs and benefits for alternation and synchrony in blue tits, Cyanistes caeruleus, using 6 years of breeding and provisioning data. This study is the first to find evidence for benefits of alternation, finding that alternation predicts indicators of reproductive success. In addition, alternation was found to be predicted by brood size. Finally, this study found evidence for sex-specific costs of alternation, finding increased mortality in females that showed high alternation, while this trend did not occur males. These results provide novel
insights into the costs and benefits of alternation, an important step in understanding whether this behaviour is adaptive.