Individual contributions to care in cooperatively breeding chestnut-crowned babblers

In this thesis, I use nestling provisioning in cooperatively breeding chestnut-crowned babblers as a measure of cooperative behaviour, and, using this measure, I investigate how and why members of the same group vary in their investment in young. Previous studies of investment have routinely used provisioning rates, rather than biomass of prey fed to young, as a proxy for investment. I show that provisioning rate closely reflected biomass delivered to the nest, making it a good measure of investment in provisioning behaviour in chestnut-crowned babblers. I explore how different components of provisioning effort (rate, prey size and type) traded off against each other in response to changes in brood demand. I show that contributions to care were strongly influenced by the interaction between the sex and age of helpers, and that observed patterns of care could only be explained by considering the costs as well as the benefits of care. Using brood size manipulations, I highlight that the effects of group size on helper contributions may well extend beyond changes in brood demand. I show that breeders and helpers did not follow the same investment rules. In particular, breeding females invested least in provisioning young. I discuss whether this strategy arose because resources were allocated to other components of reproduction. Finally, I use manipulations of provisioner:nestling ratios to demonstrate that helpers did enhance the fitness of the current brood and could therefore gain direct and/or indirect fitness benefits from provisioning young.EThOS - Electronic Theses Online ServiceGBUnited Kingdo