Pre-Feeding Agonism and Seasonality in Captive Groups of Chimpanzees (Pan Troglodytes)

Abstract Captive chimpanzees fed at regular, predictable intervals are known to exhibit higher rates of aggression immediately prior to, and during feeding. Presumably, anticipation of food creates tensions leading to increased agonistic interactions prior to feeding. This study was conducted to determine if seasonal variabilities might contribute to pre-feeding agonism. A quantitative examination was made looking at events affected by seasonal (summer versus autumn) changes. Seasonal fruit diversity and the amount of available space during feeding bouts in socially housed, captive chimpanzees were tested for an effect on pre-feeding agonism. Groups were observed for a five-week period during both seasons. Each social group was observed five times per season for 30 minutes, beginning 30 minutes prior to the morning feeding. All occurrences of agonistic behaviours were recorded. Average frequencies of agonistic behaviours were calculated for each group and compared across season using a Wilcoxon matched-pairs test to determine the effect of seasonal fluctuations in fruit diversity. There were no significant differences in the number of agonistic behaviours exhibited during summer versus autumn seasons. A strong negative correlation was found for agonistic behaviours in both seasons: as space decreased, agonism increased in both summer and autumn. In addition, males scored significantly higher in the summer versus the autumn for submissive behaviours when space decreased. The provision of a variety of seasonal fruits did not result in increased pre-feeding agonism in captive chimpanzees. In fact, cage size had a greater effect on levels of agonism than did the provision of seasonal fruits.