Reinhardt, V. 1993. Enticing nonhuman primates to forage for their standard biscuit ration. Zoo Biology 12(3), 307-312.

Ordinary feeder-boxes were converted into food puzzles by remounting them onto the mesh of the front of the cages, away from original access holes. The total amount of time [pair-housed] adult male rhesus macaques engaged in gathering the standard biscuit ration was 141 times higher at food puzzles [42.2 min] than at feeder-boxes [0.3 min]. It was concluded that using feeder‐boxes as food puzzles, baited with the standard biscuit ration, offers a cost‐ and work‐effective way to promote foraging activities in captive nonhuman primates.