Berkson, G., Mason, W. A., Saxon, S. U. 1963. Situation and stimulus effect on stereotyped behaviors of chimpanzees. Journal of Comparative and Physiological Psychology 56, 786-792.

Stereotyped behaviors are present on many occasions, but observers have noted that they are particularly prevalent when some degree of 'tension' is presumably present. ... The level of stereotyped behaviors was highest in an enclosed cubicle. This effect was apparently not related to cage size. .. Fear producing stimuli do appear to increase repetitive stereotyped movements.