Tool-Use Comprehension in Lion-Tailed Macaques (Macaca silenus)

Tool-Use Comprehension in Lion-Tailed Macaques (Macaca silenus) Susan Haverly & Peter Judge Animal Behavior Program, Bucknell University

Introduction

Discussion

Tool-use requires the manipulation of an object in the environment to achieve a goal, and requires the ability to relate one object to another.1,2,7 Many primate species use tools, both in captivity and in the wild, and tasks have been developed to test for causal understanding of the use of a tool and obtaining the goal. A common test of such tool-use comprehension involves presenting an animal with a choice between two tools, one of which is baited and can be pulled to obtain a reward, while the other tool has a reward placed in a position where pulling the tool does not obtain the reward.5 If the animal comprehends the relationship between the tool and the object on which it is acting, it should select the baited tool. The purpose of this study was to replicate this paradigm3,5 to test causal understanding in liontailed macaques, a species not previously tested for tool-use comprehension.

The results of this study indicated that liontailed macaques learned to understand the relationships between tools and the objects on which they were acting. The ability spontaneously generalized to a novel tool (Figure 5). Further, after numerous trials, two monkeys selected a tool to obtain a reward that was not obstructed by a barrier, indicating that they learned to understand the relationship between three objects: a tool, a goal, and an item in the environment.

Figure 1. Test Configurations. From Fujita, Kuroshima, and Asai (2003).

Results: All three monkeys learned to select the baited tool. Two monkeys learned in under 10 testing sessions, and the third learned in 30 sessions. Results indicated that the monkeys comprehended the relationship between the tool and the food reward.

Methods and Results Subjects: Three adult male lion-tailed macaques: Burt, Pierre, and Ranier.

Apparatus: Tool-reward configurations were placed on a wooden cart and wheeled up to the caging as choices. Hypothesis 1: Lion-tailed macaques understand relationships between tools and rewards Procedure: Using hook-shaped tools, one tool was baited with a food reward, and the other tool had the reward positioned outside the hook in twelve different configurations (Figure 1A). The twelve configurations were presented in a random order in each testing session. -Criterion for success: 10 out of 12 correct trials (binomial test p < 0.04) in two consecutive testing sessions.

Figure 3. Performances with the novel parabolashaped tools in Experiment 2. The y-axis represents the number of trials that they chose correctly. The horizontal line indicates criterion.

Hypothesis 3: Lion-tailed macaques understand relationships between tools, rewards, and barriers. Procedure: Introduced small blocks as barriers in twelve configurations to test whether monkeys could understand relations between three objects (Figure 1C). Results: Bert reached criterion in 23 sessions, and Pierre learned the task in 29 sessions. Ranier stopped approaching to test in session 13. Results indicated that two of the monkeys could understand relationships between the tool, the barrier, and the reward.

Figure 2. Performances with the hook-shaped tools in Experiment 1. The y-axis represents the number of trials that they chose correctly. The horizontal line indicates criterion, 10 out of 12 correct.

Results were the first demonstration of tooluse comprehension using this task with liontailed macaques. The macaques performed comparably to cotton-top tamarins, capuchins, and vervets in Experiments 1 and 2, and somewhat less well than capuchins in Experiment 3 when barriers were present.3,4,5 Results were consistent with similar studies indicating that Old World primates have the capability to understand tool-object relationships.6,8

References

Hypothesis 2: Lion-tailed macaques can generalize experience to a novel tool. Procedure: Introduced novel parabola-shaped tools, to test whether the monkeys could generalize to a novel tool on twelve configurations similar to those in Experiment 1 (Figure 1B). Results: Two monkeys learned to select the baited novel tool in two testing sessions, and the third learned in eight sessions. Results indicated that they generalized their previous experiences with hook-shaped tools to novel parabola-shaped tools.

Figure 5. Correct selection of hook-shaped and parabola-shaped tools.

Figure 4. Performances with hook-shaped tools and barriers in Experiment 3. The y-axis represents the number of trials that they chose correctly. The horizontal line indicates criterion.

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