Coping with rising food costs in a closed economy: feeding behavior and nocturnal hypothermia in pigeons.

The pigeon's response to increasing fixed-ratio schedules in a 24-hr closed economy is marked by changes in feeding behavior during the daily light phase and by changes in body temperature during the dark phase. The time course of these responses to increasing behavioral cost of obtaining food is very different. Feeding is most affected immediately, within the first day of exposure to moderate fixed ratios. The number of times the pigeons produce the food hopper each day decreases, and the rate at which they eat from the food hopper (grams per minute) when it is available increases, as the fixed ratio is raised. Body temperature is affected later, falling to progressively lower resting levels during the dark phase as body weight drops at the higher fixed ratios when food intake is reduced. The changes in feeding and in body temperature that occur as the fixed-ratio schedule increases seem to reduce daily energy expenditures, within the constraints imposed by the experiment. The ascending and descending limbs of the bitonic function obtained when total daily operant responding is plotted as a function of fixed-ratio schedule in the closed economy is possibly related to the occurrence of thermoregulatory strategies for energy conservation. The energetic analysis of performances in the closed economy requires consideration of a variety of energetic strategies available to the species being studied.