ASSESSMENT AND CHOICE - AN OPERANT SIMULATION OF FORAGING IN PATCHES

Pigeons were presented with an operant simulation of two prey patches using concurrent random-ratio schedules of reinforcement. An unstable patch offered a higher initial reinforcement probability, which then d eclined unpredictably to a zero reinforcement probability in each sess ion. A stable patch offered a low but unvarying reinforcement probabil ity. When the reinforcement probability declined to zero in a single s tep, the birds displayed shorter giving-up times in the unstable patch when the ratio between the initial reinforcement probabilities in the unstable and stable patches was greater and when the combined magnitu de of the reinforcement probabilities in the two patches was greater. When the unstable patch declined in two steps, the birds behaved as if their giving-up times were influenced heavily by events encountered d uring the most recent step of the double-step change. This effect was observed, however, only when the reinforcement probability in that ste p was .04, not when it was .06. All of these data agree with the predi ctions of a capture-probability model based on a comparison of the est imated probability of receiving a reinforcer in the current patch with that in alternative patches.