Long-Term Assessment of Captive Chimpanzees: Influence of Social Group Composition, Seasonality and Biographic Background

SIMPLE SUMMARY: Wild chimpanzees flexibly adapt their behavior based on many social and environmental aspects of their lives. These include seasonality and food availability as well as aspects regarding their communities and parties, such as group size, sex ratio and the presence of sexually receptive females. This results in a stimulating but also stressful life. On the contrary, housing conditions in captivity are far less stimulating, often lacking the enriching social component of fluctuating group compositions found in wild fission–fusion societies. Providing captive chimpanzees with an adequate social environment is crucial to ensure their wellbeing. We had the rare opportunity to analyze behavioral data of an all-male chimpanzee group that experienced two major group alterations, i.e., the integration of two adult females and the passing away of two adult males. Our findings highlight the importance of conducting longitudinal observations to objectively record variations in the chimpanzees’ behavior. Furthermore, we were able to demonstrate the impact of their social environment, i.e., group size and sex ratio, on the chimpanzees’ activity levels and occurrence of abnormal and self-directed behaviors. ABSTRACT: Wild chimpanzees (Pan troglodytes) live in flexible fission–fusion societies with frequent changes in both group size and composition. These changes depend mostly on resource availability and individual social preferences yet in captivity are determined by housing organizations. During a period of seven years, we observed a group of sanctuary chimpanzees, focusing on how they adapted to changes in the group composition over time. Using linear mixed models (LMMs), factors such as group size, sex ratio, seasonality, and the individuals’ sex and origin (wild caught vs. captive born) were considered in order to evaluate the impact on the chimpanzees’ activity levels, the occurrence of undesired behaviors (abnormal and self-directed behaviors) and the social grooming networks. Our results indicate that the activity levels and the occurrence of undesired behaviors were impacted by changes in group composition and the individuals’ biographic background. The colder season was marked by higher levels of activity and more time spent grooming. Moreover, it was the individuals’ origin but not changes in group composition that affected social grooming, with wild-caught chimpanzees grooming far less frequently. Long-term observations are essential to evaluate, predict and detect potential benefits and/or issues of housing conditions while considering the social and physical environment.