Fig. 2. Rates of energy expenditure (W) measured with the doubly labelled water method as a function of whether the birds were foraging (horizontal axis), subdivided into trials when they were not crushing or processing digesta (dark grey boxes), processing but not crushing (open boxes), or processing and crushing (light grey boxes). Large filled circles are least-square means and small filled circles are outliers (see Fig. 1 for a further description of box-and-whisker plots).

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