The influence of cage size and environmental enrichment on the development of stereotypies in bank voles (Clethrionomys glareolus).

Bank voles were bred and lived in 4 different environments: small barren cages (SB), small enriched cages (SR), big barren cages (BB) and big enriched ones (BR). Ten different behaviours were recorded at the age of 30, 45, 60, 61, 75 and 90 days. Between day 60 and 61, within each experimental environment, the group of voles performing stereotypies (ST) and the group of those which did not (NST) were each split in two, one part being transferred to a new environment, the other remaining in the same as control. For each of the 10 behaviours, differences between the 4 environments and therein differences between the ST and the NST animals and between the age groups were analysed with a split-plot ANOVA. The results indicated that enrichment is more determinant than cage size, as more voles developed stereotypies in SB and BB than in SR and BR. Improving the environment after day 60 inhibited the stereotypies in most ST animals, while smaller and/or barren environments elicited them in very few NST. ST voles performed significantly more rearing and walking-sniffing and showed significantly less immobility than NST ones. These differences remained linked to the ST/NST status when an animal reversed it after day 60. Within different environments, some individuals are more prone to react actively to frustration, including the development of stereotypies. The performance of stereotypies is associated with a more general behavioural activation.