Having pronounced construction instinct and activity, beavers change a lot their aquatic habitats in order to provide foraging pathways protected by water environment and create effective shelters saving them from enemies (mainly wolves and humans) and cold weather during overwintering, giving birth and raising a litter as well as everyday resting.
With respect to semiaquatic mustelids i.e. otter and mink, a question arises do these changes in aquatic habitats bring benefit for them or not? Beavers build a lot of shelters in kinds of burrows and lodges, and such a benefit of better sheltering environment for otter and mink is evident. While investigating the question, we were mainly interested in beaver activity-related increase of water-dwelling prey of otter and mink in aquatic ecosystems and, first of all, in small streams such as small rivers, brooks and drainage canals. Just at small watercourses such an effect of damming by beavers on semiaquatic mustelids may be the most pronounced. By building dams, beavers create ponds; such ponds are gradually eutrophicated and densely overgrown with macrophytes. So, it was essential to get know, such beaver ponds bring benefit in aquatic prey supply for semiaquatic mustelids or not, and if it is, on which stage of the pond eutrophication such benefit is the highest.
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