Cooperation, conflict, and the coordination of care in the long-tailed tit, Aegithalos caudatus

Parental care is costly to carers, so when multiple carers raise the same offspring, each is selected to maximise their benefit-to-cost ratio at the expense of others, causing conflict between carers over relative investment. Coordinated provisioning is hypothesised to resolve this conflict and to mitigate the costs of care. In this thesis, I investigated whether, how, and why pairs and cooperative groups of long-tailed tits, Aegithalos caudatus, performed two forms of coordinated care, alternation (i.e. taking turns) and synchrony (i.e. feeding together). In chapter 2, I used a long-term database of provisioning watches to determine whether carers coordinate their provisioning. Carers alternated and synchronised more than expected by chance, and helpers were more synchronous than breeders, although their level of coordination was not influenced by relatedness to the parents. In chapter 3, I investigated the behavioural mechanisms underlying coordination, finding that alternation was facilitated by carers actively delaying feeding near the nest if it was not their turn to feed. Synchronised feeds were facilitated by synchronous arrivals near the nest, typically led by breeding females, indicating collective foraging. In chapters 4 and 5, I conducted an experiment and analysed long-term data to test several hypotheses for the adaptive function of coordination. A high level of alternation was associated with higher provisioning rates and greater breeding productivity, as predicted by the hypothesis that conditional cooperation mitigates conflict among carers. Synchrony of nest visits across the nestling period was associated with a reduced brood predation risk in the long-term dataset, although the experimental manipulation of perceived predation threat did not cause a temporary increase in synchrony. I conclude that coordinated care in long-tailed tits is adaptive; alternated provisioning functions to resolve conflict between carers, thereby preventing exploitation, and synchronous provisioning reduces the chance that a brood’s location is advertised to predators.