The animals are now required to use manipulative foraging skills to retrieve food pieces through the mesh. No extra time is required to clean the puzzles since they are part of the cage structure. Retrieving the daily chow ration from the puzzles rather than collecting it from the ordinary food box, results in an approximately 100-fold increase of time the animals spent foraging.
Macaques only work for food that they actually consume.
This means that using the puzzles as primary feeders avoids the food spoilage problem which typically occurs when monkeys have free access to the food, hoard more than they eat and waste much of it in the process of getting food pieces into contact with fecal material. Working for their standard food rather than having free access to it has no impact on the animals' body weights. This suggests that the animals want to forage, that the act of foraging is serving them as a strong motivational reward independent of caloric intake. It goes without saying that both the ceiling puzzle and the food puzzle can also be used to feed supplemental food such as fruit, bread or vegetable, and that the animals do not lose interest in the puzzles over time. Depending on the type of food box, some remodeling may be necessary to ensure that the whole front facing the animal is covered by the mesh of the cage.