VALIDATION OF THE DOUBLY LABELED WATER METHOD IN BALD EAGLES (HALIAEETUS-LEUCOCEPHALUS) AND A COMPARISON OF 2 EQUATIONS FOR THE CALCULATIONOF ENERGY-EXPENDITURE

We validated the doubly labeled water (DLW) technique for measurement of energy expenditure in bald eagles (Haliaeetus leucocephalus) in cap tivity by simultaneously measuring metabolizable energy intake in a fe eding trial. We calculated CO2 production using two equations, one typ ically used by animal ecologists (the ''one-pool'' equation) and the o ther typically used by human nutritionists (the ''two-pool'' equation) . Metabolizable energy intake, as determined by feeding trials, for tw o adult eagles eating rats averaged 1,160 +/- 89 kJ d(-1) and for four nestlings eating fish averaged 2,124 +/- 40 kJ d(-1). Energy expendit ure measured from DLW turnover using the one-pool equation averaged 2. 2% +/- 7.1% higher than metabolizable energy intake measured by feedin g trials (not significantly different, P > 0.50), but when the two-poo l equation was used, energy expenditure measured with DLW averaged 17. 7% +/- 6.7% lower than metabolizable energy intake measured by feeding trials (significantly different, 0.025 < P < 0.05). Thus, the use of the DLW technique with CO2 production calculated by the one-pool equat ion was validated for bald eagles.