Bloomstrand, M., Riddle, K., Alford, P. L. et al. 1986. Objective evaluation of a behavioral enrichment device for captive chimpanzees (Pan troglodytes). Zoo Biology 5, 293-300.

Group-housed individuals spent on average 13 minutes per 120 minute-observation sessions contacting the puzzle box.. The most dominant males displayed the highest levels of overall use of this enrichment device. It may be desirable to use this device in groups of animals with relatively stable relationships and/or to increase the number of puzzles available to the group.