The Role of Begging and Sibling Competition in Foraging Strategies of Nestlings

In this paper we assume that parents use the signalling intensity of their young to determine how much food they bring to the nest, and that the pattern of food allocation is determined by the signalling intensity and by the intensity of other non-signalling behaviours that are not preceived by the parents and have no effect on total food provisioning. We explore the consequences of assuming different ways in which signalling and non-signalling behaviours, as well as competitive asymmetries, might interact to determine food allocation. In Model 0 only signalling affects food allocation. For the same level of need, larger (more competitive) chicks beg less and obtain a greater share of the food than their smaller sibs. In Model 1, food allocation is determined by a linear combination of the signalling and the non-signalling behaviours. When non-signalling behaviours are the main determinant of food allocation, chicks don't signal and parents bring a fixed amount of food to the nest. Larger chicks receive a greater share of this food. When both types of behaviour are equally weighted, the pattern of investment depends on competitive asymmetry. For low asymmetry levels, both chicks invest in signalling. For large asymmetries, the less competitive chick invests in signalling and the more competitive chick invests in non-signalling behaviours. In Model 2, food allocation is determined by the product of the signalling and non-signalling intensities. Larger chicks invest more in signalling and less in non-signalling behaviours. Larger chicks get more food than their siblings. A comparison of the different models shows that the chicks waste more resources when signalling evolves. Hence, if natural selection could act on the mechanism of food distribution, we would expect signalling to play a minor role in the actual pattern of allocation of resources.