Informational Constraints on Optimally Foraging Hummingbirds

I present field experiments designed to test hypotheses which account for different levels of information available to a forager. I call the information state myopic when the forager knows the location and expected quality of only one resource item at a time, and periscopic when it knows more than one. These two information states are similar to sequential and simultaneous encounter processes discussed by Waddington, but there are some differences. Foragers with periscopic and myopic information should vary their diet composition differentially as a function of relative resource quality. Foragers with periscopic information should vary the composition of their diet in a continuous manner, whereas foragers with myopic information should vary it discontinuously. Furthermore, periscopic information should generate partial preferences where foragers preferentially take those poor items nearest to rich items. I tested the predictions with free-living hummingbirds foraging on feeders designed to drain completely after a single visit. Information state was manipulated by adding or removing color cues to the feeders color indicated nectar concentration. The results support the predictions. Diet changed more sharply in response to varying resource quality when information was myopic, as opposed to periscopic. The probability of an item being exploited increased with the value of neighboring items when information was periscopic, but not when it was myopic.