Individual feeding specialization in the European mink, Mustela lutreola and the American mink, M. vison in north-eastern Belarus

Individual feeding behaviour of the European mink Mustela lutreola and American mink M. vison inhabiting the upper reaches of the Lovat river, NE Belarus was investigated. Three out of the nine individual European minks studied were specialists on frogs (mainly common frog Rana temporaria). The majority (77-97%) of their scats contained frog remains, and frogs constituted 62-88% of food biomass consumed. One European mink fed mostly on crayfish (Astacus astacus); 62% of its scats contained crayfish remains, and crayfish constituted about 61% of the food biomass consumed. The other five European minks studied were generalist predators at watersides. Three out of the ten individual American minks studied were micromammalian specialists; 86-92% of their scats contained remains of small mammals (mostly water vole Arvicola terrestris and microtines), and small mammals constituted 83-88% of food biomass consumed. The other seven American minks were generalist predators. No correlation was found between the proportion of small mammals in the diets (expressed in percentage of food biomass consumed) and their abundance in the habitats. Hence, those American minks mostly feeding on small mammals demonstrated an individual feeding specificity. In contrast, the proportions of crayfish and frogs in the diets of individual American minks was positively correlated with the abundance of these alternative prey in the habitats. This suggests an opportunistic feature in consuming of crayfish and frogs by the naturalized mink. For the European mink there was a positive correlation between the proportion of frogs and crayfish in the individual diets and the abundance of these prey in the habitats, but there was no such correlation with abundance of small mammals. The results suggest that the native mink is reluctant to prey small mammals and its opportunistic feature of feeding on crayfish and frogs. Interspecific and intraspecific food niche overlaps in minks at an individual level was estimated. Fairly large variation of the dietary similarity between the individual minks was revealed. Resource competition between the European mink and the naturalized American mink on population and individual levels is discussed.