The abundance, diet, and prey relationships of American mink Mustela vison were studied in the Słońsk Reserve (W Poland) on two plots: shore and reservoir. Estimated mink number within the Reserve was 69 in autumn–winter 1998/1999 and 50 during spring 1999. The diet of American mink consisted mainly of mammals, birds and fish. In autumn–winter, birds formed 4–16%, whereas mammals constituted up to 56% and fish up to 62% of the biomass consumed, depending on the plot. In spring and summer, however, birds formed 45–60% of the biomass consumed in the reservoir and 35–46% of the biomass taken by mink on the shore. The European coot Fulica atra was the most frequently consumed prey. In spring, mink removed 7.8% (N=278 killed birds) of coots nesting in the Reserve, 1.8% (N=9) of breeding grebes Podiceps spp. and 11.2% of ducks (N=93 taken birds). On straw platforms only 13.6% of greylag geese Anser anser broods were successful. From 35 to 77% of the nests on straw platforms were destroyed by mink. In wooden boxes 46.4% of mallard Anas platyrhynchos and 33.3% of shelduck Tadorna tadorna nests were successful. American mink destroyed 22–40% of the nests in boxes. However, the arrival of American mink to the Słońsk Reserve has not resulted in a noteworthy decrease in waterfowl populations.
We compared different methods of monitoring an American mink, Mustela vison, population in an European mink, Mustela lutreola, area. The study was carried out in the Butron basin, northern Spain. We compared sign surveys and trapping in the same non-continuous 500 m sections of river. We also radio-tagged 10 minks to evaluate the efficiency of the two methods. There was no significant association between the presence of tracks and trapping success. We noticed the presence of minks in sections where none was captured and vice versa. Furthermore, by monitoring the radio-collared minks, we found inter-sexual differences in spatial use that produced differences in the success of the trapping and sign surveys, with males using the main streams and females selecting little streams where tracks were difficult to survey. Moreover, we detected tracks in the sand of 17 minks that actively avoided the traps. Hence, 1) neither sign surveys nor trapping are reliable methods for estimating relative abundances because both are subjected to strong biases. 2) the spatial use of habitat by minks could severely affect management projects that consider only main streams and 3) projects aimed at extracting American minks need to consider those individuals that never trigger traps, females living in very small streams and the floating population living in other habitats.
A predator removal study was done in Finland to reveal the possible effects of mammalian predators on the breeding success of ducks. Predator removal/protection from hunting was most effective in northern Finland. Also in eastern Finland predator removal had some influence on predator numbers, whereas its impact on predator numbers was not so evident in southern Finland. In southern Finland, no increase in the breeding success of ducks was observed in the predator removal area, whereas in northern Finland the relative reproduction rate of diving ducks increased in the removal area and that of dabbling ducks declined in the control area. In eastern Finland, the breeding success of ducks declined in both areas. There was a positive relationship between the raccoon dog index and the relative reproduction rate of dabbling ducks in southern Finland, indicating that raccoon dog numbers probably are of minor importance for the breeding success of ducks. On the contrary, there was a negative relationship between the fox and marten indices and the breeding success of ducks in some areas. Marten and fox removal may thus have a positive effect on the breeding success of ducks in Finland. The effect of the American mink could not be verified in this study.