The influence of food size and distance on communication by chimpanzees (Pan troglodytes)

This study was designed to explore the influence of food size (small piece of banana vs. whole banana) and food distance (near, far) on communication (propensity to gesture, vocalize, and exhibit gaze alternation between food and an experimenter) by 20 laboratory chimpanzees. Of the 20 chimpanzees, 17 produced 60 gestures in the course of the experiments (only the first gesture produced in each condition was included for analysis). Neither distance nor size had any influence on Ss propensity to gesture (Wilcoxon signed ranks tests: Size, Z(19) = -.816, ns and Distance, Z(19) = -.816, ns). The size of the food did not influence Ss propensity to exhibit gaze alternation (Z(19) = -1.23, ns). The size of the food did influence Ss propensity to vocalize (Z(19) = -2.31, p = .021), which is consistent with previous studies. Distance of the food did not influence Ss propensity to vocalize (Z(19) = 1.00, ns). Distance did influence Ss propensity to exhibit gaze alternation between the food and a human observer (Z(19) = -2.65, p = .008). Distance in the present study is conflated with angular displacement between the observer and the food. In summary, larger food items elicited more vocalizations and relatively larger angular displacements elicited more gaze alternation. This latter finding suggests that chimpanzees may use their visual orienting behavior ostensively in the context of communication about distant food.