Ambient temperature and food costs: effects on behavior patterns in rats.

Eating, drinking, wheel running, and nesting were recorded continuously in animals living in cages where they foraged for and consumed food by completing operant bar-press requirements. The ambient temperature was either 24 or 0 degrees C. Two food costs, that of initiating meals and that of pellets within meals, were separately manipulated at each temperature. Compared with room temperature, the cold temperature produced a doubling of food and water intake and a greater than twofold increase in nesting time each day. Running behavior was not altered. Regardless of temperature, the cost of initiating meals influenced the frequency and size of meals but did not affect total food intake or time spent feeding, and this cost had no effect on any other activity. As the cost of pellets within meals increased, the time spent feeding increased and there was a decline in daily food intake. The change in intake was greater at the cold temperature because in the cold the rats did not increase daily feeding time sufficiently to maintain intake as pellet cost increased. Such an increase in feeding time would have required that less time be spent in one of the other activities.