1. 1994. The welfare and management of bears in zoological gardens. UFAW animal welfare research report no. 7. Wheathampstead, UK: Universities Federation for Animal Welfare.
2. 2000. The management and behaviour of captive polar bears. Ph.D. dissertation, Open University, UK.
3. A survey assessment of variables related to stereotypy in captive giraffe and okapi
4. Situation and stimulus effects on stereotyped behaviors of chimpanzees.
5. 1998. Determining the causes of stereotypic behaviors in zoo carnivores: towards appropriate enrichment strategies. In: editors. Second nature: environmental enrichment for captive animals. Washington, DC: Smithsonian Institution Press. p 172-83.