STARLINGS (STURNUS-VULGARIS) EXPLOITING PATCHES - RESPONSE TO LONG-TERM CHANGES IN TRAVEL-TIME

In this paper we explore the way foraging animals integrate experience over time. The marginal value theorem shows that to maximize long-term gain rate, foragers should adjust patch exploitation to the average travel time for the habitat, and many experiments do find a positive relationship between average patch exploitation and average interpatch travel time. This relationship implies that animals use experience to determine foraging tactics but, by itself, does not imply that anything but the most recent experience (say, the time taken to find the current patch) has an effect on behavior. We directly tested the influence of events before the most recently experienced travel by examining adjustments in foraging behavior after stepwise changes between two homogeneous environments, each with a single travel distance. Using starlings (Sturnus vulgaris) in a closed-economy laboratory simulation of a patchy environment, we found that during periods of active foraging, the average number of prey per patch visit is in close agreement with that predicted for rate maximization. After changes in travel time, birds took approximately six full cycles of travel and patch use before reaching a new asymptotic behavior. The pattern of adjustment did not vary with successive presentations of the environmental change. These results demonstrate that memory for more than one travel episode is involved in the foraging decisions of starlings. We relate our results to apparently conflicting data from previous experiments and to models of memory and information processing.