The "Feed: Drink" Decision

Abstract

The feed:drink decision is investigated in an attempt to discover how internal and external factors interact in controlling behaviour. The problem is attacked from both a functional and causal perspective. A functional approach is used in suggesting how internal and external factors should interact if the animal is to achieve a maximally efficient regulation of internal state. Here, I rely on an optimality model proposed by SIBLY & MCFARLAND (1976). Predictions made by this model are discussed, and it is shown that results from published studies on feeding and drinking in Barbary doves are not consistent with this model. It is argued that this is because animals lack information about external factor levels. This information can only be obtained by assessing the consequences of their prior behaviour. A motivational model is proposed to account for this process. Simulation experiments are done in order to reveal predictions made by this model. These experiments mimic ones that were done using Barbary doves, and it is shown that the behaviour of this model agrees precisely with that seen in these birds. The model correctly predicts effects due to behaviour interruption and changes in food and water availability. The functional implications of this model are considered by comparing simulated behaviour sequences with sequences predicted by SIBLY & MCFARLAND'S optimality model. In certain situations, there is close agreement between simulated and so-called optimal sequences. For this reason, it is argued that the motivational mechanisms described are designed to service the goal that SIBLY & MCFARLAND assumed in generating their optimality model. The goal is to regulate internal state in a maximally efficient manner.