Assessment of Behavior and Social Dynamics in a Newly-Forming Group of Captive Western Lowland Gorillas

This study presents behavioral data of a recently-formed western lowland gorilla (Gorilla gorilla gorilla) group at Riverbanks Zoo and Garden in Columbia, South Carolina, from the initial stages of group formation through the first several months after introduction. The group consists of a male (19 years), two half-sisters (both 10 years), and an unrelated female (20 years). I collected 15-minute focal animal samples for three hours twice a week in two observation blocks, the first lasting from 7/17/15 to 9/11/15, and the second lasting from 10/30/15 to 1/3/16. A total of 99.25 observation hours were collected. It was predicted that the frequency of affiliative behaviors would increase over time, with more affiliative interactions between related females. Also, it was hypothesized that agonism would decrease over time. Overall, the mean rates of affiliative behaviors did increase between the two observation blocks (rs=0.208, p=0.002, Wilcoxon Signed-Rank test); agonistic behaviors decreased (rs=-0.185, p=0.005, Wilcoxon Signed-Rank test). Dyadic rates of affiliation differed significantly (Q=39.401, p It was also predicted that a dominance hierarchy would result among the females, with the unrelated female being the lowest-ranking due to the already strong bonds shared by the half-sisters. Evaluation of female hierarchies showed there was no strong relationship among the females\u27 resulting ranks in approach-withdrawal (r=0.991, p=0.083) or grooming interactions (r=0.893, p=0.297). The results of this study show that the group-wide and intrasex relationships mirror those seen in wild populations and other captive groups, particularly in regard to the lack of social dominance. It appears that the members of newly-formed group adjusted well and will thrive in their new surroundings. Furthermore, these findings may help animal caretakers more effectively manage family groups and continue to ensure a high quality of life for captive gorillas