The motivation to inform others: a field experiment with wild chimpanzees.

Abstract

Background: Accumulating evidence indicates that some ape species produce more alarm behaviors to potential dangers when in the presence of uninformed conspecifics. However, since previous studies presented naturalistic stimuli, the influence of prior experience could not be controlled for.

Method: To examine this, we investigated whether apes (wild chimpanzees of the Budongo Forest, Uganda) would communicate differently about a novel danger (an unusually large spider) depending on whether they were with an uniformed conspecific. We tested nine adult males, four of which were exposed to the danger twice alone (Non-Social group), while the remaining five were exposed to the danger first alone and then in the presence of conspecifics (Social group).

Results: We found that both alarm calling and gaze marking (i.e., persistent gaze after stimulus detection) were more persistent in the Social than Non-Social group, although the effect of condition only reached statistical significance for gaze marking, nonetheless suggesting that chimpanzees tailored their warning behavior to the presence of others, even if they were already familiar with the potential threat.