Murchison, M. A. 1992. Task-oriented feeding device for singly caged primates. Laboratory Primate Newsletter 31(1), 9-11.

A perforated hard plastic ball loaded with peanuts was attached to the outside of the cage. The [single-housed] animals spent most of their time sitting on their cage perches [females 66%, males 36%]. Manipulating the foraging device was the second most time-consuming activity [males 22%, females 8%].