Ingestive behavior and body temperature of pigeons during long-term cold exposure

Pigeons well adapted to living in 21°C ambient temperature (T_a) were continuously exposed to cold T_a for 6 days (Experiment 1) or 30 days (Experiment 2). The pigeons lived on a 12:12 L:D cycle where they could obtain short access to food and water at any time in the light phase by making 12 keypeck responses. Across the two experiments, the levels of cold exposure were 6°C, 1°C, and 0.6°C. In cold, total daily food intake increased gradually across the first few days of the exposure, and the new level of food intake was inversely related to T_a. The daily ratio of total water drunk to total food eaten averaged approximately 1.3 in 21°C, fell to approximately 1.0 on day 1 of cold exposure, and remained at that level for as long as 30 days. The day-night cycle in core body temperature was not changed by cold exposure. The bimodal temporal pattern of feeding in the light phase, which is characteristic of pigeons in moderate T_a, was preserved in the cold although the absolute level of feeding activity was enhanced. An analysis of the ways individual pigeons achieved total daily food intake by combining a number of feeding episodes with an average amount eaten per episode revealed considerable variation between birds, but a relatively constant feeding style within bird over time. In the colder temperatures used, however, the pigeons all increased the number of feeding episodes per day. The results provide the first detailed analysis of cold-induced changes in ingestive behavior in the pigeon and raise several questions about the behavioral expression of cold-sensitive regulatory processes.