In constructing models for the explanation and prediction of feeding behaviour, it has been attempted to define the state of the animal in terms of caloric defi cit and amount of time spent eating already. These models of feeding behavior contain a negative feedback loop (caloric deficit induces feeding, which reduces deficit and increases satiation, which in turn checkes feeding) and a positive feedback loop (eating, once started, tends to persist). But it is not yet clear how the day-night rhythmicity which animal behavio are known to possess, should be incorporated in a model. In order to...