Energetic responses of pigeons during food deprivation and restricted feeding

Pigeons ate food ad lib, then fasted for several days, and finally ate a controlled amount of food once a day for several months to maintain body weight at 80% of the ad lib value. Whole-body dry heat loss (HL) and core body temperature (Tb) were measured continuously for each pigeon. Thermal conductance (C) was calculated from HL and Tb. Relative to ad lib feeding, 24-h HL was reduced by approximately 50% during fasting and controlled feeding. The majority of energy savings was achieved by lowering C, which appeared to maintain a saturated low value throughout most of the light and dark phases. Therefore, the pigeon's characteristic high Tb in the daily light phase during fasting and food restriction does not necessarily imply high energy expenditure. In the dark phase, the fasting pigeon's characteristically low Tb enhances energy savings already being achieved through lowered C. The daily cycle in Tb, and to a lesser extent in HL and C, was strongly altered by occasional probe variations in the amount of food given at the single daily feeding and by a shift in the time of the daily feeding.