Importance of Energy Costs in Central Place Foraging by Hummingbirds

E-ISSN： 1939-9170|70|1|195-205

ISSN： 0012-9658

Source： Ecology, Vol.70, Iss.1, 1989-02, pp. : 195-205

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Abstract

I tested predictions from three models of central place foraging (CPF) in two field experiments with Calliope Hummingbirds (Stellula calliope). The models were based on different "currencies," or optimization critieria: (a) maximization of net rate of energy intake while foraging and traveling between a central place and feeding areas; (b) minimization of proportion of total time spent foraging and traveling; (c) maximization of energetic efficiency while foraging and traveling. All three models differ from most CPF models in that I assumed that gross rate of energy intake while foraging in a patch remained constant. Net rate of energy intake decreased with time spent foraging because the cost of hovering flight increased during foraging bouts due to the accumulating mass of ingested nectar. In a dual choice experiment repeated with the same male in two years, I offered a choice between a "fast—weak" feeder that provided a fast instantaneous energy intake rate but low sucrose concentration (low energy/mass ratio), and a "slow—rich" feeder with slow instantaneous intake rate and high concentration (high energy/mass ratio). As predicted by all three models, the male preferred the fast—weak feeder when the feeders were near his central place, and he increased his relative use of the slow—rich feeder when they were farther away. In another experiment in which I offered only one type of feeder at a time, males increased meal size with travel distance from their perches to feeders, and took larger, heavier meals from fast—weak than from slow—rich feeders. Both of these results were predicted by the time minimization and efficiency maximization models, but not the rate maximization model. Females who were incubating or feeding young did not change meal size significantly with travel distance from their nests to feeders. This qualitative result was predicted by the rate maximization model but not the time minimization and efficiency maximization models. Females took larger, heavier meals from slow—rich than from fast—weak feeders, and this was not predicted by any of the models. Mean meal sizes of both males and females were smaller than predicted by any of the models at all travel distances.