Lambeth, S. P., Bloomsmith, M. A. 1994. A grass foraging device for captive chimpanzees (Pan troglodytes). Animal Welfare 3, 13-24.

In the wild, chimpanzees spend most of their time foraging, so any device that stimulates this behaviour in captivity could potentially be effective enrichment. A simple grass foraging device constructed of a polyvinyl chloride (PVC) pipe cut in half lengthwise and planted with rye grass seed was designed to allow captive chimpanzees living in non- grassy enclosures to exhibit foraging similar to that of their wild counterparts. The grass containers were attached to the outside of six different enclosures. Observational data were collected on 14 adult chimpanzees (eight females, six males) within groups of either two or four members. A total of 54 hours of behavioural observations were conducted and comparisons were made across three conditions: baseline; grass container; grass container with extra foraging material (one half cup of sunflower seeds). Subjects used the grass container 4.0 percent of their time, but for 19.8 per cent of their time when the grass container [was loaded] with extra foraging material. There was no statistical evidence of habituation to the device. Overall, the grass container only increased time spent foraging when it contained additional food items. Since behavioral benefits associated with this device are few, its potential application is limited.