Time-Budget Estimates of Avian Energy Expenditure: Physiological and Meteorological Considerations

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Abstract
Daily energy expenditures ( ) of aviary-housed budgerygahs (Melopsittacus undulatus) were estimated simultaneously using doubly labeled-water (DLW) and timebudget (TB) methods under summer and winter conditions. Laboratory validation of the DLW technique displayed excellent agreement with concomitant gravimetric measures of CO₂ production (algebraic mean difference = -0.04%; range = -5.2%-6.2%). The aviary studies combined continuous 24-h recording of each bird's daily activities with quantification of its thermal environment (wind speed and air and operative temperatures). Activity and thermoregulatory costs of birds used for TB studies were measured in the laboratory. Comparison of predicted by DLW to values predicted by the TB method indicate that measurement of activity costs at the time of the study and their subsequent evaluation through existing heat-transfer models are equally important to determining reliable energy budgets. Avian TB studies that fail to address these concerns are prone to systematic biases in their estimates of .