Wildlife ResearchBehavioral studies on the use of open water basins by American mink (Neovison vison)
Introduction
The behavioral needs of farmed mink, including access to “swimming water,” have been the topic of debate and of several scientific investigations. In the wild, American mink (Neovison vison) are semi-aquatic mustelids whose living habits often are associated with various types of water supplies such as streams, riverbanks, and lake shores (Dunstone, 1993). The results of Zschille et al. (2004) confirmed that feral American mink prefer water bank habitats in eastern Germany. These mink are opportunistic predators which live mostly on fish, amphibians, and crustaceans but also hunt rabbits and other prey on land (Wiepkema and de Jonge, 1997). For example, Wolff et al. (2015) found that in Illinois, USA, the site occupancy by mink was related positively to the presence of local areas with high crayfish concentrations (hotspots), instead of local habitat characteristics that might indicate high prey densities.
Many studies have dealt with the question whether swimming is an essential behavior pattern for mink (Cooper and Mason, 1999, Hansen and Jeppesen, 2001a, Mason et al., 2001, Vinke et al., 2006, Ahola et al., 2011). A number of publications offer supporting evidence for this hypothesis: Several preference tests, in which mink had to work for resources, showed that swimming water was the most valued resource (other resources tested included an alternative nest site, toys, a raised platform, a tunnel, and an empty cage; Mason et al., 2001). Cooper and Mason (2001) show that there was no difference in the maximum “price” paid for the access to food and a swimming bath. In a comparison of the demand of farm mink for a swimming bath versus a running wheel revealed that mink accepted the running wheel and the swimming bath equally, even when one of the resources was offered for free, whereas the price for the other was increased (Hansen and Jensen, 2006a). The use of the running wheel may be associated primarily with locomotion, whereas the use of the swimming bath may be associated with exploration behavior (Hansen and Jensen, 2006a), possibly meeting different needs or desires (Hansen and Jensen, 2006b).
Farmed mink typically do not have the opportunity to swim or dive because their cages lack water pools. Standard wire cages for the accommodation of one breeding mink, or one female with litter, or one juvenile male plus one juvenile female in the growth period until pelting are approximately 85 cm long, 30 cm wide, and 45 cm high (total area: 2,550 cm2) and connected to an additional wooden nest box (ZDP, 2015). The food is placed directly on the mesh wire on top of the cage, and drinking water is offered in nipple drinking troughs. The German Fur Animal Breeding Association (ZDP, 2015) currently is testing so-called “family cages” on commercial farms in Germany. Those are cage systems on multiple levels, enriched with “rest and play areas” (total area: 6,429 cm2 without nest box), where the female remains with her kits until their sexual maturity (ZDP, 2015). However, these cages do not offer any swimming opportunities and do not meet the requirements of the German “Order on the Protection of Animals and the Keeping of Production Animals” (Tierschutz-Nutztierhaltungsverordnung, 2006).
Based on the biology of wild mink, European animal welfare recommendations suggest that swimming is an essential behavior pattern for mink, and therefore, a swimming basin should be provided for farmed mink (Council Directive 98/58/EC; Council of the European Union, 1998). In 2006, the German “Order on the Protection of Animals and the Keeping of Production Animals” (Tierschutz-Nutztierhaltungsverordnung, 2006) amended and published on August 22, 2006, last changed on February 5, 2014, stated mandatory husbandry requirements for mink for the first time in Germany. These requirements (with a transition period until 2016) include a water basin for swimming, a platform, and a nest box. Therefore, the purpose of this basic pilot study was not to prove whether swimming is a behavioral need or not. It was the aim to investigate if and to what extent farmed mink use swimming water as environmental enrichment, and to analyze which kind of water basin is suitable to allow mink to perform swimming and diving behavior to a large extent. An assessment of water quality and temperature was also conducted.
Section snippets
Subjects and experimental design
The study was carried out at a research center of the Ludwig-Maximilians-University Munich, Germany, from the end of July through the beginning of December 2007. Forty American mink (N. vison) were housed in 2 identically constructed free-range enclosures, with a size of approximately 300 m2 each (Figure 1). Every enclosure housed 20 mink (groups A and B). This double approach was deliberately chosen, to have a simultaneous replication of the experimental set up. The animals were bought from a
Behavior
For the analysis of water contacts derived from the direct observation data, basic summary statistics were computed for the number of visits at the water basins for each observation week as shown in Table 2 and Figure 2. There was no substantial difference between the 2 groups. The mink visited each of the 3 water basins, but the numbers of visits were not evenly distributed. With increasing age of the mink, the number of water contacts increased. Furthermore, we observed a generally greater
Discussion
The results of the direct and the video observations showed that the mink in both groups (A and B) generally accepted all 3 water basins and used them from the beginning to the end of the study. As the main objective was to assess the usage of the different water basins and compare them with each other, we observed the animals during their main activity times, instead of recording the use of the resources for 24 hours. During the day, the animals spent most of their time in the nest boxes, with
Conclusion
The animals in this study generally accepted all 3 water basins and used them extensively from the beginning to the end of the study; therefore, a swimming basin can be considered to be an important enrichment factor for American mink. As it could be expected due to the large and fully enriched housing conditions, it was possible to keep young mink in groups with free access to swimming water basins without the occurrence of any stereotypies. Further studies should be undertaken to investigate
Acknowledgments
This work was supported financially by the German Federal Ministry of Food and Agriculture (BMEL, Bonn, Germany) through the Federal Office for Agriculture and Food (BLE, Bonn, Germany), grant number 03HS061. The funding source played no role in study design; in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication. The idea for the article was conceived by Angela Schwarzer. The experiments were designed by
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2017, Journal of Veterinary Behavior: Clinical Applications and ResearchCitation Excerpt :Twenty American mink (N vison) were housed in a free-range enclosure with a size of approximately 290 m2 (Figure 1A). For a general overview of the enclosure, see Schwarzer et al. (2016). The animals were bought from a commercial mink farm after weaning at 9 weeks of age and kept in a quarantine facility for 3 weeks, in aviaries (2 × 2 m) without water basins.
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