Public influence on social structure and habitat uses in captive western lowland gorillas (Gorilla gorilla gorilla) in a naturalistic enclosure

Details

Supervisors

Hance, Thierry

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie, à finalité approfondie

Abstract

The present study analyzes how the presence of visitors affects the interactions and habitat use of a group of western lowland gorillas (Gorilla gorilla gorilla) living in a naturalistic enclosure. By relating the position of individuals, with an exposed/unexposed zone approach, to different visitor variables (density; movement or activity) acquired along two adjacent paths, we assessed how different situations of visitor presence influence gorilla behaviors. Our results suggest that visitors generally reduced inter-individual distances, accentuated by environmental factors such as wind, temperature, and humidity. Social network analysis revealed an intensification of contact, particularly between females and their offspring, as well as an increase in comfort and resting behaviors in the presence of visitors. Rather than large, immobile crowds, the presence of new visitors moving into the most exposed zone induced more retreat into the Distal (unexposed) zone, in contrast to the second possible zone, where visitors are harder for the gorillas to see. Overall, the different scenarios for the presence of visitors led to significant aggregation, contrasting with a quasi-random distribution without visitors. A new contribution is the introduction of the Retreat Index (RI), which indicates an individual's tendency to retreat into the unexposed zone, and the Exposure Tolerance Index (ETI), which quantifies individuals' tolerance of exposure to the sight of visitors. We also used Ripley's K and L functions, for the first time directly on individuals, revealing various spatial distribution patterns under different visitor configurations. This pilot study establishes a comprehensive protocol for analyzing the effects of visitors on captive gorillas, applicable to most housing conditions, which will need to be replicated to mitigate inter-individual variation and provide a global view of captive populations. Our methodological innovations shed light on the complex interaction between visitor presence, gorilla behavior and space use, and provide a basis for future investigations that will improve our understanding of the factors affecting gorilla dynamics in captivity.