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Figure 1


Fig. 1. Schematic representation of Eqn 1 and 2, showing our conceptualization of a bird's energy balance. Birds gain energy during foraging and lose energy when traveling between food patches. The switch between these modes is instantaneous. (A) The general case where energy gain, En(tp), and the power required for flight, P(tt), are functions of time (Eqn 1). (B) The simplification used in this study where En and P are constant over time (Eqn 2). The total travel time is in both cases calculated by the sum tt={Sigma}itt(i) and the time spent foraging is calculated by tp={Sigma}itp(i). Note that P is given in positive values in Eqn 1 and 2, so that -P is used on the negative part of the vertical axis.





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