Gottlieb, D. H., Ghirardo, S., Minier, D. E. et al. 2012. Efficacy of 3 types of foraging enrichment for rhesus macaques (Macaca mulatta). JAALAS 50(6), 888-894.

The 3 enrichment devices had different effects on individual expression of stereotypy: supertubes decreased it, shakers increased it, and puzzle balls led to a decrease followed by an increase. We present potential reasons for the changes in stereotypy and postulate a likely balance between the beneficial and negative effects of enrichment in any given environment.