Mason, G. J. 1991. Stereotypies: a critical review. Animal Behaviour 41, 1015-1037.

Stereotypies are physically or temporally associated with lack of stimulation, or events such as acute stressors or the expected arrival of food. All these environments may involve chronic conflict and frustration and hence stress. Other stereotypies are relatively independent of the current environment, but reflect a past challenge severe enough to have traumatic effects on the central nervous system. Thus the acquisition of stereotypies indicates an environment that is probably inadequate, and as such, presumably aversive.