Validation of the Doubly Labeled Water Technique in Small Insectivorous Bats by Comparison with Indirect Calorimetry

Abstract

The doubly labeled water technique (DLW) for the measurement of free-living energy expenditure was validated by comparison with indirect calorimetry for nine small (<10 g) insectivorous bats (n = 7, Pipistrellus pipistrellus; n = 2, Plecotus auritus) over a fivefold range of daily metabolism. The DLW estimates were consistently greater than the indirect calorimetry estimates. The mean algebraic difference was +9.5% with the Lifson and McClintock equation, +5.1% with the Coward et al. equation, and +3.4% with the Schoeller et al. equation. These differences were not significant since the range of errors was large. Mean absolute deviation was 13.5%, 13.7%, and 14.5% for the three respective equations. The assumption of a constant respiratory quotient (RQ) did not introduce significant error. The overestimate of energy expenditure made by the DLW technique is consistent with previous validation studies on mammals. One potential source of this error is that the fractional turnover of the oxygen label includes...