Maple, T. L., Finlay, T. W. 1987. Post-occupancy evaluation in the zoo. Applied Animal Behaviour Science 18, 5-18.

We investigated the effects of translocating great apes from barren cages to innovative naturalistic habitats. ... For both gorillas and orangutans, the new environment had the effect of reducing the variety and frequency of aggressive interactions. ... In the complex environments, fights could easily be avoided or shortened by escape to cover. In addition, for the gorilla pair, pro-social behavior occurred to a greater extent in the new environment. Some behaviors, such a play-biting, were recorded for the first time in the new enclosure. Both gorillas were prone to regurgitation and re-ingestion in their former cages. However, in the naturalistic environments these abnormal behaviors were never observed.