Line, S. W., Markowitz, H., Morgan, K. N. et al. 1989. Evaluation of attempts to enrich the environment of single-caged non-human primates. In: Animal Care and Use in Behavioral Research: Regulation, Issues, and Applications . Driscoll, J. W. (ed), 103-117. Animal Welfare Information Center National Agricultural Library , Beltsville, MD.

A review of early studies of enrichment for single-housed primates. Our experience with cage toys suggests that after a very short time (a few days or less), most macaques will lose interest in the objects that are offered. Rhesus macaques removed monkey biscuits from a puzzle feeder despite the fact that the same kind of food was available free-choice at the twice-daily feedings.