Activity rhythms and use of nest boxes of juvenile mink in seminatural group housing

The aim of this study was to investigate the activity patterns of American mink (Neovison vison). Twenty mink from a commercial mink farm were housed in a free-range enclosure (290 m2) at the age of 13 weeks. In the enclosure, the mink were offered 20 nest boxes (animal-to-nest-box ratio: 1:1), food ad libitum, and 3 kinds of water basins. The activity rhythms and the use of the nest boxes were assessed by an automatic registration device that recorded the amount of time spent inside or outside the nest box or in the entrance tunnel for each individual mink over a period of 18 weeks between July and December. In addition to analyzing the mink's daily and seasonal activity patterns, we sought to detect any social preferences or preferences for individual nest boxes. Results showed that the mink had crepuscular activity patterns with 2 activity peaks during dusk and dawn and that the former shifted when the daylight period shortened. Throughout the experiment, the activity time spent outside the nest boxes declined with increasing age and decreasing ambient temperature. In addition, the mink showed a preference for nest boxes that faced the feeding lots and not the water basins. During sleep and rest periods, the mink spent high amounts of time using the nest boxes in company. Furthermore, the mink structured their own habitat by using certain nest boxes for sleeping and others as latrine boxes. Small differences between male and female mink existed in their activity (i.e., time spent inside or outside nest boxes) but not in their preference for certain nest boxes or other individuals. Based on our results, any environmental enrichment item should be presented all day long, so each mink has the opportunity to use them individually during their main activity times mostly at dusk and dawn, and their daily handling should be adjusted to this rhythm. A mink-to-nest-box ratio of 1:1 does not seem necessary as juvenile mink often slept in groups of 2 or more animals in 1 nest box. Furthermore, the animals should be given the opportunity to distinguish between a sleeping and a latrine area.