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.