Manipulation without mind-reading: information suppression and leakage during food discovery by mandrills (Mandrillus sphinx)
Publication Type: |
Journal Article |
Year of Publication: |
2006 |
Authors: |
Mark E. Laidre |
Publication/Journal: |
Behaviour |
Keywords: |
cognition, concealment, food calling, manipulative communication, passive deception, theory of mind |
Abstract:
At an ultimate, evolutionary level, manipulation entails behaviour that enhances the fitness of the manipulator even if at times inflicting a cost on the fitness of the manipulated. At a proximate, mechanistic level, mind-reading entails an ability on the part of a manipulator to attribute beliefs to those it manipulates. Both manipulation and mind-reading were investigated during a study of food-associated calling by semi free-ranging mandrills in Gabon. Mandrills were initially provisioned at a feeding cage (whose opening generated loud noises) and under these conditions calling occurred at high rates, particularly among middle-ranking individuals. When mandrills were then fed away from the cage (where potential alerting cues were absent) the calling rate dropped drastically and discoverers of the resource suppressed loud calls, producing only soft grunts. The latter conditions provided an increased opportunity for solitary consumption, and analyses showed that discoverers benefited substantially in terms of ingested food from a reduced presence of group mates. Loud calls, however, were produced by later arrivals and a correlation existed between the production of these calls and more group mates arriving at the resource. Loud calls may have enabled later arrivals to access monopolized resources, since by divulging information they could attract other, particularly lower-ranking group mates whose arrival engendered a diversion. Withholding calls (information suppression) and producing calls (information leakage) thus each appeared functionally manipulative, their usage depending only on whether they benefited the signaler. Acoustic playbacks were consistent with this hypothesis: compared to controls, food-associated calls resulted in more arrivals and also a trend toward quicker resource depletion and increased consumption by mandrills other than the discoverer. Yet upon hearing playbacks of a group mate’s calls, non-vocal discoverers consuming the resource did not disguise their actions in anticipation of their group mates’ arrival. In fact, some of their actions (like making repeated forays with unconcealed food) appeared wholly inconsistent with mind-reading.