Murphy, D. E. 1976. Enrichment and occupational devices for orangutans and chimpanzees. International Zoo News 137(23.5), 24-26.

A heavy metal cylinder, 60 cm long and 45 cm in diameter, was capped on each end and bolted to a platform. Three 8 cm holes in the cylinder allowed access to the inside. A short section of a rubber hose was chained near one hole in the cylinder. The chimps were able to use the hose as a tool in a manner similar to fishing for termites or opening a beehive in the wild. The chimpanzees rapidly emptied the container of their morning meal with ingenious manipulation and intense interest. .... Chimps and orangs manipulated their feeders even though ample food was available. On days when the device could be operated by the orangutans, they were observed climbing in the structure about thirty per cent more often than when the device was not operating. There was an apparent increase in general activity. The most encouraging result was a reduction in the female's stereotyped pacing. The environmental enrichment of the chimp exhibit has resulted in a decrease in observable coprophagy, a diversification of the activities, and a probable improvement in the physical and psychological condition of the animals. No data are included in this article.