Winter food caches of beaversCastor fiber Linnaeus, 1758 were examined in 16 locations within the Suwałki region (north-eastern Poland). Four caches were selected to represent each of four habitat types: river, lake, farmland, and oligotrophic small reservoir called ‘suchar’. Altogether, 92 509 twigs and branches of 15 woody species were identified and measured. Individual caches, with one exception, included branches of only 4 or 5 species. WillowsSalix sp., birchesBetula sp., alderAlnus glutinosa, trembling aspenPopulus tremula, and mountain ashSorbus aucuparia occurred in caches from all four habitats studied. Willows alone constituted 62.5% of the total number of branches cached. Willows, together with birch, hazelCorylus avellana, alder, and trembling aspen, amounted to 97% of all branches in caches. The remaining 10 species provided only 3% of the branches cached. Most branches were 0.5–1 m long and <3 cm thick at their base. Contents of food caches provided a good indication of winter diet and possibly food preference of beavers.