Rats (Rattus norvegicus) and pigeons (Columbia livia) are sensitive to the distance to food, but only rats request more food when distance increases

Abstract

Three experiments investigated foraging by rats and pigeons. In Experiment 1, each response on a manipulandum delivered food to a cup, with the distance between the manipulandum and the cup varying across conditions. The number of responses made before traveling to collect and eat the food increased with distance for rats, but not for pigeons. In Experiment 2, two manipulanda were placed at different distances from a fixed food source; both pigeons and rats preferentially used the manipulandum closest to the food source. Experiment 3 was a systematic replication of Experiment 1 with pigeons. In different conditions, each peck on the left key increased the upcoming hopper duration by 0.5, 1.5 or 2.5s. Completing a ratio requirement on the right key of 1, 4, 8, 16 or 32 pecks, depending on the condition, then produced the food hopper for a duration that depended on the number of prior left pecks. As the ratio requirement increased on the right key, pigeons responded more on the left key and earned more food. Overall, the results replicate previous research, underlining similarities and differences between these species. The results are discussed in terms of optimal foraging, reinforcer sensitivity and delay discounting.

Figure 1

Responses per trip for pigeons (top panels) and rats (bottom panels) in the first (left panels) and second (right panels) cycles. Error bars represent the standard error of the mean.

Figure 2

Relative response ratios as a function of the relative manipulanda-food source distances (M-S distances; log-log coordinates) for pigeons (left panel) and rats (right panel). Each data point represents the average response ratios pooled across animals. R₁ refers to the right manipulandum, and D₁ its M-S distance; R₂ refers to the left manipulandum, and D₂ to its M-S distance. Error bars represent the standard error of the mean.

Figure 3

Pecks per trip on the provisioning key as a function of the FR value on the collect key. Circles, triangles, and squares represent the hopper step sizes of 0.5, 1.5, and 2.5 s, respectively; error bars represent the standard error around the mean.