Dynamic Aspects of Foraging Decisions: Short-Term Caching Strategies

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Decisions made by animals are affected by numerous factors. For example, a bird's choice among different food items can be shown to be affected by how hungry the bird is, the relative abundance of food types, the sequence of previous encounters with different food items, and the amount of fat reserves the bird has stored. Until now, it has proved difficult, both theoretically and experimentally, to study the combined effects of these factors in a meaningful way. As a result, only a small fraction of the rich diversity of responses that animals exhibit have been studied. The current pilot project is designed to test techniques that will allow a more synoptic view of animal decision-making. Specifically, Dr. Lucas plans to test several predictions of caching behavior by Carolina chickadees under laboratory conditions. Chickadees store food items singly in hundreds of different sites and retrieve this food within a period of days. The predictions, derived from a dynamic-programming model, will be tested by continuously monitoring body mass, cache size and caching decisions throughout the day. Monitoring will be accomplished using computer-driven electronic balances and remote sensors in potential cache sites. This work is important because it provides a methodology for understanding behavior in a broad context. Decisions should reflect a balance of costs and benefits associated with alternative behaviors available to the animal. The costs and benefits, in turn, are affected by current conditions and expected changes in these conditions. This is as relevant to human behavior as it is to the behavior of non-human animals. Caching behavior is particularly revealing because, by caching food, the animal is providing for future nutritional requirements (when the food is retrieved) to the detriment of current requirements (which could be satisfied by eating discovered food immediately). Thus, caching decisions should reflect current conditions and expected changes in those conditions when the food is finally retrieved.