Hierarchical position of individual captive western lowland gorillas Gorilla gorilla gorilla and its impact on neighbour associations and behaviour

Abstract

This study investigated the social relationships observed within a captive breeding group of western lowland gorillas Gorilla gorilla gorilla at a European Association of Zoos and Aquaria (EAZA) accredited facility: Blackpool Zoo, UK. Gorillas are complex and intelligent primates, and the western lowland sub-species is popular in zoo collections. Captivity can raise issues for gorillas which, in the wild, live in large family groups with a distinct hierarchy forming the basis of group stability. Studying captive groups can help facilities make informed decisions for gorilla captive management. This study considered if and how captive gorilla behaviour could be influenced by social positioning. It was carried out in May–July 2018 and focused on social behaviour, nearest neighbour and position in the enclosure recorded for focal individuals with notes on enclosure design taken. Interval focal sampling was used to record gorilla (n=6; two adult females, one adult male, two juvenile females and one infant male) social behaviour, their nearest neighbour (the animal physically closest to the focal individual) and position in the enclosure simultaneously every 10 min, during six-hour observation periods over two months. A different individual was observed daily. Data on independent and social behaviours were collected to determine activity budgets using an ethogram. Data on independent behaviours can demonstrate if there are variations in behaviour when gorillas are in social proximity. Mann-Whitney U tests were conducted on mean frequencies of independent (n=10) and social (n=5) behavioural categories for each individual. Independent inactive behaviours were most common (n=53.6) with adult gorillas displaying increased levels of sitting and lying in comparison with younger individuals. There is a
difference among the gorillas in their social behaviour. Nearest neighbour data were analysed using cluster analysis. The silverback was most closely associated to his youngest offspring and lactating female. The sub-adult female has the weakest associations in comparison to the rest of the group. The results suggest individual preferences for social associations, with younger individuals associating closely with their mothers, and a mother and infant associating closely with the silverback. A sub-adult female was less associated with all individuals, which could suggest her readiness to transfer. This study emphasises the influence that hierarchical social organisation within a captive setting has on captive gorilla behaviour monitoring in general, relating to how individual gorillas manage their position in a hierarchical group. This study also provides specific suggestions for gorilla management within the centre and in conjunction with BIAZA guidelines, including a suggestion to relocate the sub-adult female to a new group and considerations for aggression mitigation.