of food first only when the feeders had covers. When access to food was made easy by leaving feeders open, rats fell back on a linear strategy of visiting every feeder in spatial order. A strategy of sampling all food sources may be the rat's default option unless access to food is made difficult. From this point of view, the selective foraging seen when different quantities of food are placed on the ends of a radial maze may arise from the travel time required to run up and down the arms of the maze.
A final example of what appears to be hard-wired decision rules is found in central place foraging on the radial maze. Rats begin to carry large food items to the center of the maze on the first day of testing. After as many as 50 days of testing, food-carrying functions like that seen in Fig. 1.8 are still found. Although rats are never interrupted during testing sessions and certainly no predators appear, rats continue to behave as if the center of the maze is a place of safety to which large pieces of food must be carried. One evolutionary basis for this behavior may be the wild rat's burrow structure, in which central chambers are built with a number of escape routes or bolt holes ( Pisano & Storer, 1948). The center of the maze may be a preferred place to consume food because it offers the greatest number of escape routes. Both the difference in handling times for food eaten on an arm and in the center and the difference in return travel times when carrying and not carrying food reinforce the conclusion that rats perceive the center of the maze as considerably safer than the arms.
The radial maze appears to have considerable ecological validity for the study of foraging in rats. Although it has traditionally been used as a tool for the investigation of memory ( Olton, 1978; Roberts, 1984), it appears that its use can now be extended to the study of several kinds of foraging in rats. Further, experiments on the radial maze appear to be providing us with considerable information about the functional use of memory in animal foraging.
Preparation of this chapter was supported by Grant A7894 from the National Sciences and Engineering Research Council of Canada.
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