Role of begging and sibling competition in foraging strategies of nestlings

We assume that parents use the signalling intensity of their young to deter mine how much food they bring to the nest, and that the pattern of food all ocation is determined by the signalling intensity and by the intensity of o ther nonsignalling behaviours that are not perceived by the parents. We exp lore different ways in which signalling, nonsignalling behaviours and compe titive asymmetries might interact to determine food allocation. In Model 0 only signalling affects food allocation. More competitive chicks beg less a nd obtain a greater share of the food than their smaller siblings. In Model 1, a linear combination of signalling and nonsignalling behaviours determi nes food allocation. When nonsignalling behaviours are the main determinant of food allocation, chicks do not signal and parents deliver a fixed amoun t of food. Larger chicks receive a greater share of this food. When both ty pes of behaviour are equally weighted, the pattern of investment depends on competitive asymmetry. For low asymmetry levels? both chicks invest in sig nalling. Por large asymmetries, the less competitive chick invests in signa lling and the more competitive chick invests in nonsignalling behaviours. I n Model 2, the product of signalling and nonsignalling intensities determin es food allocation. Larger chicks invest more in signalling and less in non signalling behaviours. Larger chicks get more food than their siblings. Ove rall 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 res ources. (C) 2001 The Association for the Study of Animal Behaviour.