Starlings (Sturnus vulgaris) exploiting patches: response to long-term changes in travel time

In this paper we explore the way foraging animals integrateexperience over time. The marginal value theorem shows thatto maximize long-term gain rate, foragers should adjust patchexploitation to theaverage travel time for the habitat, andmany experiments do find a positive relationship between averagepatch exploitation and average interpatch travel time. Thisrelationship implies that animals use experience to determineforaging tactics but, by itself, does not imply that anythingbut the most recent experience (say, the time taken to findthe current patch) has an effect on behavior. We directly testedthe influence of events before the most recently experiencedtravel by examining adjustments in foraging behavior after stepwisechanges between two homogeneous environments, each with a singletravel distance. Using starlings (Sturnus vulgaris) in a closed-economylaboratory simulation of a patchy environment, we found thatduring periods of active foraging, the average number of preyper patch visit is in close agreement with that predicted forrate maximization. After changes in travel time, birds tookapproximately six full cycles of travel and patch use beforereaching a new asymptotic behavior. The pattern of adjustmentdid not vary with successive presentations of the environmentalchange. These results demonstrate that memory for more thanone travel episode is involved in the foraging decisions ofstarlings. We relate our results to apparently conflicting datafrom previous experiments and to models of memory and informationprocessing.