Limitations on the effectiveness of environmental improvement in reducing stereotypic behaviour in bank voles (Clethrionomys glareolus)

Bank voles (Clethrionomys glareolus) from three age groups were transferred from conditions in which stereotypic behaviour reliably developed to conditions in which stereotypies rarely developed, to test if environmentally induced stereotypies become independent of their causal factors. Forty-eight voles were used, aged 2 months (Young: n=18); 6 months (Mid: n=14); and 14 months (Old; n=16) at the start of the experiment, All had been bred and housed in conventional laboratory cages, in which roughly half of each age group had developed locomotor stereotypies. Half of the voles were housed in a small cage with no vegetation (barren) and half the voles in a larger cage, containing hay and twigs (enriched). After 60 days, the voles were swapped from one treatment cage to the other, Their behaviour was recorded on three occasions in each cage (after 5 days, 30 days and 55 days) on video for 30 min following an unfamiliar stimulus (ball point pen rattled along roof of cage). Voles usually ran or dug in the barren cage, and remained motionless in the enriched cage, immediately following the rattle. There was no evidence of habituation to the rattle. Eight Young, six Mid and 12 Old voles performed stereotypies in the barren cage and three Mid acid ten Old voles also performed stereotypies in the enriched cage. No Young voles performed stereotypic behaviour in the enriched cage, so stereotypies were harder to disrupt through environmental enrichment in older voles. Voles that performed stereotypies had a shorter latency to move and spent less time inactive than voles that did not perform stereotypies, in all age groups and both environments, except for Young voles in the. enriched cage. These moved later and spent more time inactive in the enriched cage if they had been found to stereotype in the barren cage. This suggests that young stereotyping voles are more responsive to aversive stimuli than non-stereotyping voles, but that their specific behavioural response to the rattle is context specific, In an environment with plenty of cover, young stereotyping voles remain immobile, whereas they respond more actively when little cover is available.