McClure, D. E., Thomson, J. I. 1992. Cage enrichment for hamsters housed in suspended wire cages. Contemporary Topics in Laboratory Animal Science 31(4), 33 (Abstract).

Golden Syrian hamsters (n=99) were housed individually in suspended wire cages so that spilled food and excreta could be removed. After 8 days, the hamsters developed bizarre aggressive behavior which consisted of growling, hissing, aggressive posturing toward humans, destruction of water bottle rubber stoppers, and attacking objects introduced into the cage. Many developed inappetence which progressed to anorexia, depression, and unresponsiveness. ... When cotton nestlets were provided to all of the hamsters, their appetite and responsiveness improved, but the aggressive behavior remained unchanged. The nestlets were replaced by a 13-cm length of 5.5-cm-diameter polyvinyl chloride pipe (PVC). The water bottles were replaced by an automatic watering system. After adding the PVC, the aggressive behavior diminished in 3 days and was unnoticeable in 14 days. In conclusion, when these hamsters were provided with nesting material their well-being was improved as indicated by resolution of inappetence and depression. Providing the PVC apparently resolved the aggressive behavior problem by providing a means for seclusion in addition to functioning as a burrow and as a toy.