Field Bioenergetics: Accuracy of Models and Methods

Abstract

Doubly labeled water (DLW) estimates of field metabolic rates (M) and feeding rates (I) in free-living terrestrial vertebrates should be accurate to within ± 119%. In comparison with simultaneous DLW measurements, time-energy budget (TEB) determinations of M may be more than 40% too low, 55% too high, or very accurate. No one TEB model tested to date has been accurate in all cases. To yield reliable results, future TEB studies of small endotherms should include field measurements of operative temperature (Te) and wind speed, and fresh laboratory measurements of the energetic costs of various activities should be done. The assimilation method for estimating I involves field measurements of production (growth and reproduction, or population mortality) along with estimates of M in the field, and it yielded reasonable results in one study on lizards. The field feces collection method has yielded apparent underestimates of I in two situations. The radiosodium turnover technique for measuring I is promising for animals having simple diets, and this method should be tested under field conditions. Potentially, the most profitable approach in field bioenergetics studies is the inclusion of several of these methods simultaneously, so that one method may cover for the shortcomings of another, and the results will be richly detailed.