Fig. 5. Daily intake in experiment 3 increases as a function of the daily available foraging time T_n. Values are means ± S.E.M.; intake is expressed both as number of prey (left axis) and in metabolizable energy intake (right axis). The rate of increase (i.e. the intake rate) is similar across the three treatments (2, 6 and 16 h; P>0.95), and is correctly predicted by shell mass per prey and the flocks' average gizzard mass (G=8.13 g; broken line based on the parameters of experiment 1; P>0.85), and is much lower than the rate of prey-handling (1/H, broken line; P<0.001). These observed intake rates were close to the postulated upper limit (grey bar; Kirkwood, 1983; Kvist and Lindström, in press). The thick solid line gives daily expenditure for G=8.13 g. The experimental birds would just balance their daily energy budget when feeding for 12 h (arrow), which is exactly the time that is naturally available in their intertidal habitats. If the birds had had smaller gizzards (thin solid lines indicating gizzard mass G in g), they would have needed more time for this (even though their daily requirements would go down somewhat - this is not plotted here, but see Piersma et al., 2003).

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