Same Space, Different Species: The Influence of Exhibit Design on the Expression of Zoo-Housed Apes’ Species-Typical Retiring Behaviors

SIMPLE SUMMARY: Chimpanzees and gorillas in the wild make nests in which to sleep, made from branches, leaves, and other foliage. Chimpanzees typically make their nests in the trees, by bending over branches, whereas gorillas tend to gather materials to form a nest on the ground. We were interested to know if such species patterns in sleeping elevation would be shown by zoo-living apes. We observed a group of six chimpanzees and a group of four gorillas for two 3-month periods in which they inhabited one of two similar indoor/outdoor exhibits, such that each group was observed in both of the exhibits at different times. Specifically, we considered their location while performing retirement behaviors between 3 and 5 p.m. when they settled down for the night. Both species used the exhibits similarly in that in one exhibit, both species nested in elevated locations, whereas in the other, both species tended to nest on the mulch floor. This suggests that particular characteristics of the exhibit spaces affected where and how the apes retired for the night, while the expected species differences that we know from wild populations were not evident. Understanding how the design of zoo exhibits can affect ape behavior will be useful to those seeking to encourage natural patterns of activity. ABSTRACT: Wild chimpanzees frequently make arboreal nests, while wild lowland gorillas typically nest on the ground. We aimed to understand whether zoo-housed apes’ use of elevated spaces for retiring similarly differed between species and across exhibits. Using a pre-planned exhibit switch at Lincoln Park Zoo (Chicago, USA), we compared where (elevated or terrestrial) two groups of apes (Pan troglodytes and Gorilla gorilla gorilla) performed retiring behaviors (inactive, sleeping, and nest-building behaviors). We studied a group of six chimpanzees and a group of four gorillas in two exhibits of similar size and configuration for two three-month periods (between 3 and 5 p.m.) before and after the groups switched exhibits. We predicted that chimpanzees would be more likely to retire in elevated locations compared to gorillas, irrespective of the exhibit. We found a significant effect of exhibit on where the apes retired but no effect of species, such that both species were more likely to retire in elevated locations in one exhibit but not the other. This suggests that the specific characteristics of the exhibits (e.g., number of visual barriers) influenced the expression of the apes’ retiring behaviors. These findings offer further insight in how exhibit design can influence the expression of natural behaviors in these species.