Gorilla Activities and Social Behavior: Assessing Changes Associated with Absence of Zoo Visitors, Zoo Attendance, Time of Day and Increasing Maturity

In this study we report on associations found between several variables and changes in gorilla behavior. Two groups of gorillas were observed, one was a family group and the other was a bachelor group. The zoo was closed to visitors for two periods during the COVID-19 pandemic which made it possible to document any differences associated with the presence and absence of visitors. We also considered possible changes in behavior in relation to daily zoo attendance, time of day, and increasing maturity of group members. Output variables included six activities and one location which were assessed by instantaneous sampling, as well as level of aggressive and affiliative behavior assessed by recording all occurrences. Hour in which observations were done and successive months in the study, which serves as a measure of increasing maturity of younger gorillas, were the best predictors of activity and location, with each showing significant relationships with three output variables. Absence of visitors during zoo closure was also significantly associated with an increase in time the gorillas were proximate to potential visitor viewing areas. Aggression among the bachelors was lower when the zoo was closed and higher with maturation of the youngest male. Reviewing differences in level of aggression during the two periods of closure shows that decreased aggression among the bachelors was not a result of zoo closure.