Mechanisms of Patch Choice by Bluegills (Lepomis macrochirus) Foraging in a Variable Environment

Abstract

Using an automated shuttlebox system, we conducted patch choice experiments with bluegill sunfish (Lepomis macrochirus) to assess their response to differences in food availability between patches. We also describe strategies bluegills use when choosing between patches. Five experiments, in which the difference in food availability between patches decreased from experiment to experiment, were run over a 4 mo period. Bluegills responded to differences in food availability as small as 25% between patches. Bluegills appeared to use a proximal patch-leaving rule similar to that suggested by Green (1980). Previous day's experience (memory) was used to make initial patch choices at the start of each day, but bluegills continued to sample both patches during an experiment. When the location of the better patch was exchanged with that of the poorer patch, bluegills began foraging in the poorer patch but quickly modified their patch preference, particularly when food available differed substantially between patches. Sampling of the poorer patch continued even when food availability remained constant for 7 d. The proportion of time spent in the two patches paralleled predictions from matching theory; the proportional amount of time spent in a patch was equivalent to its value relative to the total value of the environment. These patch-choice strategies seem appropriate for animals such as bluegills which are generalist foragers living in a variable environment.