Dynamic Aspects of Foraging Decisions: Short-Term Caching Strategies

动物的决定受到许多因素的影响。例如，鸟类对不同食物的选择可以受到以下因素的影响：鸟类的饥饿程度、食物种类的相对丰富程度、之前遇到不同食物的顺序以及鸟类储存的脂肪储量。到目前为止，无论是在理论上还是在实验上，都很难以一种有意义的方式研究这些因素的综合影响。因此，在动物表现出的丰富多样的反应中，只有一小部分得到了研究。目前的试点项目旨在测试能够更全面地了解动物决策的技术。具体来说，卢卡斯博士计划在实验室条件下测试对卡罗莱纳山雀缓存行为的几种预测。山雀在数百个不同的地方单独储存食物，并在几天内取回这些食物。这些预测来自动态规划模型，将通过全天持续监测体重、缓存大小和缓存决策来进行测试。监测工作将在可能的贮藏地点使用计算机驱动的电子天平和远程传感器来完成。这项工作很重要，因为它提供了一种在广泛背景下理解行为的方法。决策应反映与动物可选择的其他行为相关的成本和收益的平衡。成本和收益反过来又受到当前条件和这些条件的预期变化的影响。这与人类的行为和非人类动物的行为一样相关。贮藏行为特别能说明问题，因为通过贮藏食物，动物提供了未来的营养需求（当食物被取回时），而损害了当前的需求（可以通过立即食用发现的食物来满足）。因此，缓存决策应该反映当前条件和最终取回食物时这些条件的预期变化。

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.