Interactive Effects of Temperature Acclimation and Dietary Fatty Acids on Metabolic Rate and Body Composition of Zebra Finches (Taeniopygia guttata).

Climate change is contributing to geographic range shifts in many bird species, with possible exposure to novel diets. How individuals respond physiologically across chronic time frames to the interacting effects of diet and environmental temperature has been little explored. We acclimated zebra finches to either cool (20°C-24°C) or thermoneutral (35°C) temperatures over 6 months and provided them with diets enriched in either unsaturated or saturated fatty acids. We measured body mass throughout the study, and basal metabolic rate (BMR) and body composition at 3 and 6 months, respectively. Individuals held in cool conditions and fed a diet enriched with unsaturated fatty acids lost mass relative to the other groups, and after 6 months were of similar mass to individuals maintained at thermoneutrality. Chronic exposure to cool conditions increased BMR and the mass of the pectoral muscle and visceral organs. However, we could detect no long-term effect of diet on any physiological parameter. Our results contrast with those of birds studied over acute time frames, in which diet and temperature interact to determine energy expenditure. Over chronic time frames individuals appear to reach a new steady-state, with long-term physiological responses driven primarily by thermoregulatory responses to environmental temperature.