Doubly labelled water validation in the marsupial petauroides volans

Amounts of carbon dioxide (CO₂) produced by caged greater gliders were measured simultaneously by means of potassium hydroxide absorption, and by the low-level, doubly labelled water method, which incorporated a gas isotope ratio mass spectrometer for determining the low oxygen isotope enrichments. The two methods yielded significantly different values, but doubly labelled water underestimated CO₂ production by only 8·3% on average, and this error is in the range of mean errors found in previous validation studies where no significant differences existed. In addition, we tested procedures designed to reduce the costs of using the doubly labelled water method, by streamlining field and laboratory procedures for sample handling and processing.