Reinhardt, V., Roberts, A. 1997. Effective feeding enrichment for non-human primates: A brief review. Animal Welfare 6(3), 265-272.

There is a growing awareness that non-human primates kept in zoos and laboratories deserve more species-appropriate stimulation because of their biological adaptation to a challenging environment. Numerous attempts have been made to effectively emulate the gathering and processing aspects of natural feeding. Whole natural food-items, woodchips mixed with seeds, the puzzle ceiling and the puzzle feeder stocked with ordinary biscuits, cost little or nothing but induce sustained food gathering and/or food processing. Turf and fleece substrates sprinkled with particles of flavoured food, foraging trays, probe feeders and puzzles baited with food treats also promote more foraging behaviour, but they are relatively expensive and require added labour time to load and clean them.