Meder, A. 1992. Effects of the environment on the behaviour of lowland gorillas in zoos. Primate Report 32, 167-183.

The purpose of this study was to observe as many gorilla groups as possible and to compare their behaviour in different exhibits, social structures and visitor situation. Gorillas were studied in 15 zoos, they lived in 14 groups with male and female adults and immatures, 2 groups of adults without immatures, 3 adult pairs, 2 solitary silverbacks and several groups of immatures. The gorillas lived in 17 indoor and 11 outdoor enclosures with glass (15), moat (11) and bars (2). Data of behaviours were collected by one-zero sampling (locomotion, dominance, display, aggression, positive contact, social play, abnormal behaviours, watching of the visitors, visitor- directed display), the whereabouts of each group member by scan sampling. Visitor number and activity was observed with scan and one-zero sampling. The number of different movable objects was negatively correlated with watching the visitors. The enclosure's floor space was not correlated with frequencies of the observed behaviours. In spacious enclosures the gorillas did not like to stay in the open but usually spent most time near structures, especially the walls of niches. In enclosures with several compartments they frequently retreated from the group by staying in a separate room, no matter whether it was visible for the public or not. If the compartments were very small and not furnished, only those individuals used them for considerable time, that were pregnant or seeked privacy for other reasons. Rest areas above the ground and climbing structures were used particularly in small enclosures without any other privacy, but even in spacious outdoor exhibits. Solitary silverbacks and adults in pairs showed more interest in visitors than adults in groups. Males in 2-male-groups did not behave differently from males in 1-male-groups. The number of group members was positively correlated with locomotion, aggressive and positive social behaviours (correlation of female aggression with the number of adult females in a group was also observed in free-ranging gorillas). Frequency of noncompliant behaviour in visitors did not differ with enclosure types and the presence of signs or barriers. In enclosures with a moat barrier the gorillas observed the visitors more frequently, in enclosures with glass they spent more time near the visitors; glass seems to be most effective in reducing the disturbances by visitors, and even more, if an additional space with plantings separates visitors and gorillas.