Central Place Foraging: Optimal Load Size for Net and Gross Energy Maximizers

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Abstract
The theory of multiple-prey loading of Orians and Pearson considers the optimal patch residence time, or optimal load size, for a forager that is assumed to maximize a certain rate of energy delivery to the central place, e.g. a nest. Kacelnik and Houston based their analysis of optimal load size for net and gross energy maximizers on the assumption of similar loading curves for the two strategies. I show here that this assumption is fulfilled only in the special case when the metabolic rate while searching equals the metabolic rate while handling prey. When the two cost rates are not equal, net and gross energy maximizers will have different prey choice and hence different loading curves. The sign of the difference in optimal load size between the two strategies will depend on the difference in loading curves and the travel time.