Quantitative evaluation of the motivation to access a running wheel or a water bath in farm mink

The purpose of the series of experiments presented here was to quantify the priorities of mink for swimming water and running wheel, respectively, by construction of demand functions for each of the two resources by use of operant conditioning techniques. In all the experiments, the mink were kept individually in experimental cages that could be equipped with either a box of swimming water, a running wheel, or both resources at the same time. Each water box or running wheel was presented with a connected lever response manipulandum. The mink worked on a fixed ratio (FR) schedule (5, 10, 20, 40 and 60) for access to the resource (the reward). Eight 1-year-old females of the colour type Scan Brown were used and the reward duration was 2 min.In experiment 1, the mink had access to only one of the two resources at the same time. In experiment 2 they had access to both resources at the same time, while in experiment 3 they could work for one of the resources while they were given free access to the alternative resource. Finally, experiment 4 tested running wheel against either full or empty water box as a control.There were no differences in the elasticity of the demand for swimming water and for a running wheel, indicating that mink value these two types of cage enrichment equally high. However, a higher intercept and consequently a larger area under the demand curve for wheel than for water show that mink use the wheel much more than the water. Simultaneous access to both resources did not affect the elasticity of either swimming water or running wheel. Furthermore, the mink did not increase their use of the free running wheel as the price of swimming water was increased, or their use of free swimming water as the price of running wheel increased. Therefore, the two resources did not appear to substitute for each other. Both a running wheel and swimming water were valued higher than access to an empty water box. The mink used the running wheel mainly during their normal activity periods, whereas the swimming water was primarily used in the morning when the mink were feed and the water box refilled. The motivation for using swimming water seems to decline rather quickly. Based on the lack of substitutability between the two resources and the different diurnal patterns, it is suggested that different motivations underlie the use of these two resources. Use of the running wheel may represent a motivation to perform locomotive activity whereas use of swimming water may represent other motivations, such as exploratory behaviour.