Lam, K., Rupniak, N. M. J., Iversen, S. D. 1991. Use of a grooming and foraging substrate to reduce cage stereotypies in macaques. Journal of Medical Primatology 20(3), 104-109.

We examined the effects of a synthetic fleece pad on cage stereotypies in individually housed cynomolgus monkeys. Animals exhibited idiosyncratic repertoires of stereotyped behaviour, including repetitive pacing, swaying circling, bouncing, cage charging, and rocking that occupied on average 11% of baseline observation periods prior to the introduction of the enrichment gadget. Animals who received the fleece alone engaged in grooming which was associated with an increase in time spent resting. Monkeys given fleece pads sprinkled with morsels of food did not groom the fleece, but rather foraged for long periods (up to 27 min/h). Stereotyped behaviours were reduced by up to 73% by use of the fleece pad both alone and with foraging crumbles.