Winter distribution and abundance of mustelids and beavers in the river valleys of Białowieża Primeval Forest

Lutra lutra, Mustela vison, M. putorius, M. erminea, M. nivalis, and the settlements of Castor fiber were surveyed along 170 km of rivers in Białowieża Primeval Forest (Poland and Belarus), the best preserved temperate lowland forest in Europe. The censused rivers varied from very small (1-5 m wide, <1 m deep) to medium-sized (11-15 m wide, up to 3 m deep). Mustelids were counted by tracks left in snow.