Variation in withholding of information in three monkey species

Abstract

Studies on tactical deception have reported that informed subordinates can withhold information from naive dominants, but they have not directly compared species' performance. Here, we compared the performance in two withholding-of-information tasks of three monkey species differing in the strictness of their dominance hierarchy and degree of fission-fusion dynamics: spider monkeys, capuchin monkeys and long-tailed macaques. Food was hidden from the dominants' view either inside an opaque box or in a transparent box that could only be opened by knowledgeable subordinates. All species were capable of withholding information, with subjects refraining from interacting with the box when the dominant was nearby. Spider monkeys were the most efficient at retrieving food, by timing it when the dominant was far from the box. Capuchin monkeys were also quite efficient when alone at the box, but they lost much of the food when manipulating the box with the dominant nearby. The results supported our predictions based on interspecific differences in the strictness of the dominance hierarchy and the degree of fission-fusion dynamics, with the former constraining the subjects' tendency to approach the box and the latter affecting the subjects' tendency to wait for the appropriate situation to retrieve the food.

Figure 1.

Experimental set-up for the two tasks. (a) In OB, the subordinate subject (S) is informed about the presence of a preferred food item hidden inside an opaque box, while the dominant partner (D) is not informed. (b) In CB, the preferred food item is visible to both S and D, but only S is informed about the way to access it, by first taking the peg off, secondly pushing the box open and finally retrieving the food.

Figure 2.

Percentage of trials in which the food was retrieved by the subject, by the dominant or by nobody, as a function of task, species and subjects’ strategy (alone: the subject only approached the box without the dominant; together: the subject approached the box together with the dominant; no attempt: the subject never approached the box). (a) Opaque box and (b) clear box. White bar, dominant retrieves food; grey bar, nobody retrieves food; black bar, subject retrieves food.