DAILY ENERGY-EXPENDITURE OF TUFTED DUCKS - A COMPARISON BETWEEN INDIRECT CALORIMETRY, DOUBLY LABELED WATER AND HEART-RATE

1. The doubly labelled water (DLW) technique has been used to estimate the rate of energy expenditure of many species of free-living birds including some that dive. The technique, however, has never been validated in an actively diving bird. 2. DLW was used to estimate the metabolic rate of the diving tufted duck and the derived estimate was compared with the value obtained by direct respirometry. All the equations used to calculate the energy expenditure from DLW produced estimates for individual birds with large ranges of errors. Even the most accurate equation, S4 (Speakman 1993), underestimated oxygen consumption by an average of 15.6%. The range of errors for that equation (-83 to +67%) shows that in the diving tufted duck, the DLW technique has a reduced precision. 3. This reduced precision is probably due to the high water flux measured. As a high water turnover is likely to be a consistent feature of many diving and swimming birds and mammals, care should be exercised in interpreting measurements derived from DLW for these animals. 4. Heart rate, used as another indicator of metabolic rate, was also monitored in four of the birds. Although there was again a wide range of individual errors (-38 to +71%), the mean estimate was not significantly different from those derived from DLW and direct respirometry.