Nestling begging offers a resolution to the theoretical conflict of interest between parent and offspring over resource allocation. By begging a nestling provides accurate information about its requirements, and this enables parents to distribute the resources in a way that maximises parental productivity. The recent literature confirms the basic relationships between offspring need, begging signals and parental provisioning responses. However, little attention has been paid to the repeated suggestion that nestlings learn about their feeding environment and adjust their begging behaviours in order to maximise the probability of being fed. Male and female adult Southern Grey Shrikes, Lanius meridionalis, are shown to differ in the amount of food they deliver to
the nest and also the position from which they offer prey. I test the potential for
nestlings to respond to these differences by presenting food from consistently different feeding locations at an artificial nest. Shrike nestlings are indeed able to adjust their behaviour on the basis of new information. Whilst the first feed that a shrike nestling received had a disproportionate influence on their position within the nest, they soon moved away from this location in order to favour a more profitable feeding zone.
Interestingly, this was true when the quality of a feeding zone was adjusted both in relation to delivery rate but also the size of prey offered and this is the first study to demonstrate such a learned response to environmental profitability. The potential for such competitive positioning was also assessed in a cavity nesting species, the Pied Flycatcher (Ficedula hypoleuca), with parental food delivery however, successful manipulation of the delivery ratio to different sides of the nest proved problematic. Whilst begging in the presence of parents may secure parental resources within the current feeding visit, or even increase the overall provisioning rate of the parents, begging in the absence of a parent would appear wasteful. 'Parent absent' begging events were found to represent 15% of all begging events in nestling shrikes and a significant decrease was recorded with increasing nestling age. Whilst there was some evidence that hunger was the motivation to beg in the absence of a parent, parent absent
begging events were found to occur in clusters, with the interval preceding the first event longer than the interval between subsequent events. These results are discussed in the context of differential costs of begging in successive events in addition to the sensory development of nestlings.
The importance of the delivery ratio of prey was also considered in the context of
digestion and the development of nestling hunger. Nestlings differed in the efficiency of digestion according to the nature of prey delivery. Nestlings hand-fed small prey frequently, had more protein present in their faeces than nestlings provisioned the same total volume of food in large infrequent packages. These differences in digestive efficiency were reflected in nestlings fed small prey demonstrating a higher begging intensity than their sibling after a period of food deprivation. These results suggest that subtle differences in the feeding history of an individual can influence its 'need', and the potential for nestlings to adjust their digestion is discussed in relation to the competitive nest environment and the evolution of honest signals of need.
In summary, the focus of this thesis is to consider the flexibility of nestling responses, both behavioural and physiological, to a potentially variable nest environment. As such, this thesis provides an insight into the begging behaviour of a novel species and also investigates a number of questions new to the study of begging.