Nest building in birds has long been assumed to be a behaviour that is not learned, despite suggestive evidence to the contrary. In this thesis I investigated the role of learning in nest building in birds. I focused primarily on the choice of nest material made by zebra finches, in particular between two or more colours of nesting material. Using this aspect of behaviour, I found that adult nest building birds changed their preference for a particular colour of nesting material depending on their own nesting and breeding experience: males that built a nest using material of their less preferred colour later preferred that colour following a successful breeding attempt in that nest. In contrast to this role for learning in adults, in two other experiments I found no evidence that juvenile birds learned about the nest from which they had fledged or that birds learned about what material to nest with from conspecifics. Using wild Southern masked weavers, I also addressed variability in a particular aspect of nest building: the attachment of the very first blade of grass knotted onto a branch. I found that birds did not construct the same attachment each time they did it, even when building at the same location, but that males generally used more loops in their attachments as they built more nests, and when using longer pieces of grass. Finally, I tested zebra finches on a nest building ‘task', using a paradigm often used to test cognitive abilities among tool-users. Birds were presented with two lengths of nest material, one of which was more appropriate for one of two sizes of nest box entrance. I found that nesting birds could choose the appropriate length of material and that the birds' handling of material and their choice of material changed with experience. Taking these results together, it seems that there is a greater role for learning in nest construction than is generally acknowledged and that nest building might involve the same underlying cognitive processes as tool manufacture and use.

A surge of recent work elucidating a role for learning and memory in avian nest-building behaviour has challenged the long-standing assumption that nest building develops under genetic control. Whereas that work has been addressed at describing the cognitive mechanisms underpinning nest-building behaviour, almost nothing is known about either the neurobiological processes controlling nest building or the selection pressures responsible for the diversity in avian nest-building behaviour. Here, I sought to identify both the neural substrates involved in nest-building behaviour and some of those selection pressures. First, I used expression of the immediate early gene product Fos, an indirect marker of neuronal activity, to identify brain regions activated during nest-building behaviour in the brains of nest-building and control zebra finches (Taeniogypia guttata). I found that neural circuits involved in motor control, social behaviour, and reward were activated during nest building. Furthermore, I found that subpopulations of neurons that signal using the nonapeptides vasotocin and mesotocin and the neurotransmitter dopamine located within some of these neural circuits were also activated during nest building, suggesting these cell-signalling molecules may be involved in controlling nest-building behaviour. Next, I found that variation in the amount of folding in the cerebellum, a brain structure thought to be involved in manipulative skills, increased with increasing nest structural complexity, suggesting that the cerebellum is also involved in nest building. Finally, using evolutionary statistical models, I found support for the hypothesis that nest-site competition off-ground and increased predation pressure on the ground in Old World babblers (Timaliidae) led to the co-evolution of building domed nests on the ground. Here, then, I provide the first evidence of potential neural substrates controlling and selection pressures contributing to variation in nest-building behaviour.