Fig. 3. A comparison of the estimated metabolic rates found in this indoor study (filled circles) with a doubly labelled water-estimate obtained in a similar study on an outdoor intertidal flat (Poot and Piersma, 1994; filled triangle). In this outdoor study it was calculated that the thermostatic costs amounted on average to 0.88 W. Thermostatic costs were absent in our indoor study. We therefore subtracted 0.88 W from the outdoor metabolic rate (open triangle) to make the metabolic rates from both studies comparable (note that this assumes the additive energy budget model is operative - see main text). This `thermoneutral' outdoor metabolic rate is correctly predicted by combining the three indoor activity-specific cost estimates with the outdoor time budget (7.2 h of available foraging time per day, of which 71% was actually spent foraging). Values are means ± S.E.M. HIF, heat increment of feeding.