Many invertebrates and vertebrates rely on tree cavities for shelter, protection from predators, roosting and nesting sites, and these cavities are often a limiting resource. In many ecosystems, cavity-nesting species create a structured community that interacts through the creation of, and competition for, cavities for roosting or nesting purposes. At Mogalakwena, we distributed 80 nestboxes in different habitats over the reserve. These boxes will allow us to study in detail the competition for nesting cavities. Birds are the most likely candidates to occupy boxes, but other animals like bushbabies, squirrels and bees are also likely candidates. We are especially interested in the three hornbill species that occur on the reserve: the African grey, southern yellow-billed and southern red-billed hornbills are very similar in size and behaviour and we would like to know how they coexist in the same area. This project has the potential of collecting observational data on the behaviour of parents, e.g. looking at provisioning behaviour, but also on the consequences for the chicks by looking at their growth and survival.