Using the doubly-labeled water (DLW) technique, we measured the CO2 production of six free-living male Savannah Sparrows (Passerculus sandwichensis, mean mass 19.1 g) and found a mean (±1 SD) of 7.28 ± 1.36 ml CO₂/ h. Assuming an R.Q. of 0.85 and 24 J/ml CO2, we calculated a mean ḢTD (daily energy expenditure) of 80.3 ± 16.6 kJ/day. Simultaneously to our DLW measurements, we constructed time budgets for the sparrows during their normal activities with the intent of exploring the agreement between predictions of a number of time-energy budget (TEB) models from the literature and DLW measurements. Our results reveal that several models yield reasonable results, the mean value for the models of Kendeigh et al. (1977), Walsberg (1977), and Mugaas and King (1981) differing from DLW measurements by only +4.7, -5.6%, and +5.7%, respectively. Comparisons of ḢTD as predicted by these TEB models between species and within species between nesting phases might be made with some confidence. However, the variation in TEB estimates is not related to variation in DLW measurements within our study. This precludes statements about differences between individuals.
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Williams et al. (1984) studied this question.