Age and Context Affect the Stereotypies of Caged Mink

The effects of age and context on the stereotypies of caged mink were examined in order to assess the developmental changes undergone by the behaviour, and to find context-specificity that might suggest its motivational bases. Caged mink perform stereotypies consisting of a variety of movements, most commonly pacing and rearing, running in and out of the nestbox, and stationary head-twirling or nodding. Stereotypies are largely performed as feeding-time approaches, and many mink do not show them at all once fed. Stereotypies become more frequent and less variable with age; and in adults, individuals with the highest levels of stereotypy show the least variable forms of the behaviour and are most likely to perform it in more than one context, i.e. not solely in the pre-feeding period. These data suggest that mink stereotypies become 'established' with age, in the manner described for stereotypies in other species. However, the behaviour of kits does not follow the pattern seen in adults: kits performing stereotypies in more than one context do not have particularly high levels of the behaviour, nor are their stereotypies particularly unvarying. In addition, post-feeding stereotypies are commonly shown even by very young animals. Thus it cannot be the case that mink stereotypies are performed first in the pre-feeding situation and only later in other contexts via a process of emancipation. This conclusion is further supported by the finding that the forms of the behaviour often differ pre- and post-feeding. The specific forms and contexts of mink stereotypies suggest certain motivational bases for the behaviour. The rise in stereotypies as feeding time approaches and the sustained levels seen when the animals are not fed indicate hunger as an important factor, and in one dataset, the individuals whose stereotypies were solely pre-feeding used the most Longitudinal movements (i.e. pacing and its variants). This suggests that stereotypies, and pacing movements in particular, may stem from appetitive, food-searching behaviour. In contrast, Stationary movements such as head-twirling are performed more in the hours after feeding, and in one group of mink their levels declined over the pre-feeding period as feeding time approached. The physical appearance of such movements suggests they might be derived from attempts to escape the cage. Thus mink stereotypies areprobably seen in a range of contexts because they develop from several different behaviour patterns, with different motivational bases. The link, in adults, between performance in this range of contexts and the degree of establishment of the behaviour may be explained in one of two ways. In one adult group the data suggest that animals with stereotypy in more than one context incorporate the typically post-feeding Stationary movements into their pre-feeding behaviour, as if emancipation of this movement had occurred. However, data from the other adult group do not support this hypothesis, and the degree of establishment and the number of contexts in which stereotypies are performed may not be causally linked at all, but instead the independent products of individual propensities to develop stereotypic behaviour. Sex and site differences have yet to be fully explained. Females show consistently higher levels of stereotypy than males, as if perhaps they find the environment more frustrating. There are also enormous differences in the frequency and incidence of the behaviour on the two different sites studied.