The Neighbor Effect in Bachelor and Breeding Groups of Western Lowland Gorillas (Gorilla gorilla gorilla)

Abstract

Behavioral monitoring is an essential tool for understanding how animal management decisions, including exhibit design choices, impact animal behavior and welfare. The purpose of this study was to use behavioral monitoring techniques to determine the interaction between 2 groups (bachelor and breeding groups) of western lowland gorillas that are housed in separate habitats that partially face one another. We performed simultaneous, 30-minute group observations on the breeding and bachelor groups and recorded all occurrences of agonistic and affiliative behavior, vocalizations, and visual monitoring of the adjacent group. At 5-minute intervals, we also recorded which gorillas in the observed group were potentially visible to the neighboring group. Our results indicated that there was considerable variation in the percentage of time each gorilla spent monitoring the neighboring group. We were also able to demonstrate that the visibility of individuals in the breeding group of gorillas was related to behavior of the gorillas in the bachelor group. Although non-contact aggression increased with the visual presence of the adult male of the breeding group, more severe aggression that could cause injury was not influenced by his presence. Results also showed an association between visual presence of a particular female in the breeding group and a decrease in contact aggression in the bachelor group. Since many zoological exhibits allow visual access to other animals, it is important to determine the impact that neighbors may have on each other. Our study investigating interactions between neighboring gorilla groups is an example of how behavioral monitoring can be used to assess the impact of a wide range of management decisions on animal behavior and welfare.