Nocturnal digestion, cloacal excretion, and digestion-related thermogenesis in pigeons (Columba livia).

Two indicators of nocturnal digestive activity were identified in pigeons. Experiment 1 showed that a sizable amount of food empties from the crop while pigeons are inactive during the night. Experiment 2 showed that the number and volume of cloacal droppings during the night were directly related to the volume of food consumed during the day. The temporal pattern of cloacal droppings in the night was systematically related to features of the nocturnal body temperature (Tb) curves, suggesting that excretory activity is thermogenic in its own right and/or that it is a marker for a thermogenic process in the upper digestive tract. Questions about the relationship between digestion-related thermogenesis and shivering thermogenesis during the night in birds are highlighted by these findings.