Brent, L. 1992. The effects of cage size and pair housing on the behavior of captive chimpanzees. American Journal of Primatology 27, 20 (Abstract).

Environmental manipulation was higher and inactivity lower in the [furnished] large single cage than in the [furnished] small single cage. The mean abnormal behaviors decreased in the larger cages but the difference was not significant. ... During the paired condition, the subjects spent approximately 11% of the observation time in socially directed behaviors.