Emerging relationships in a new group of Western lowland gorillas Gorilla gorilla gorilla at Riverbanks Zoo & Garden, Columbia, SC

Abstract

Behavioural interactions among members of a newly formed group of Western lowland gorillas Gorilla gorilla gorilla are analysed, from the early stages of group formation through the first several months after introduction. The group consisted of a male, two half-sisters and an unrelated female. Data were collected in 15 minute focal animal samples for 3 hours twice a week in two 9 week observation blocks for a total of 99·25 observation hours. Hypotheses tested included: frequency of affiliative behaviours would increase over time, with more affiliative interactions between related females; and agonism would decrease over time. Overall, the mean rates of either behaviour type did not change between observation blocks (affiliative: P = 0·075; agonistic: P = 0·116) Total dyadic rates of affiliation were different in female–male dyads (P < 0·001) but not in female–female dyads (P = 0·525). Dyadic mean rates of agonism from both observation blocks were not different in either female–male or female–female dyads (P = 0·210). Using data from approach–withdrawal and grooming interactions, no strong dominance hierarchy was found among females, despite the relatedness of two of the three females. In general, the focal group exhibited group-wide and intrasex relationships similar to those documented in other gorilla groups in zoos and in the wild, particularly with regard to the lack of consistent female social dominance.