In my laboratory, two macaque monkeys are housed together in an indoor cage measuring 2 m wide by 2.6 m high x 2 m deep. A movable partition down the center of the cage makes it possible to separate the monkeys when experimentation requires it. They are separated for feeding and when one of the monkeys is to be transferred to a training room elsewhere in the building.
One monkey is a slow eater and one is a fast eater. To ensure that the slow eater gets her full food ration, we open the partition down the center of the living cage only part way, fastening the partition in the half-open position with a bolt and wing nut. The smaller (slow-eating) monkey can get through the opening to visit the larger (fast-eating) monkey, but the larger monkey cannot cross over to the smaller one's area. We leave the smaller monkey's food ration on "her" side, so that she can eat at leisure, and the larger monkey cannot have access to her food ration. But they are free to be together whenever the smaller monkey elects to visit the larger monkey's cage area. (The smaller monkey could also steal food from the larger monkey, but that's not a problem because he eats up his ration quickly.)
The monkeys' indoor cage also opens to an outdoor exercise area measuring 1.9 m wide by 2.7 m high by 6 m deep. The monkeys are allowed outside for an hour or two of exercise each morning (somewhat longer on weekends), and brought back indoors later for feeding and experimentation.
Both their indoor and outdoor cages are equipped with hanging tires and ropes. This has not entirely solved the problem of boredom, however. They quickly tire of durable new toys; other toys are quickly destroyed and consumed. One activity that keeps both monkeys busy for quite awhile each day is sifting through a deep pile of wood shavings that covers the floor of their outdoor cage. It is baited daily with small bits of cereal. At times when it is not essential to monitor each monkey's food ration we also bait the wood shavings with Purina monkey chow or small bits of fruit and vegetables. Their chow is mixed with a little yogurt each day. They like the yogurt, eat their chow much better, and have fewer problems with diarrhea since they began eating yogurt daily.
Chamove, A.S., Anderson, J.R., Morgan-Jones, S.P., Deep Wood Chip Litter: Hygiene, Feeding, and Behavioral Enhancement in Eight Species. International Journal for the Study of Animal Behavior Problems. 3 (4), 1982, pp. 308-318.
Reproduced with permission of the editor. Published in Humane Innovations and Alternatives Vol. 1, 1987, p. 6.