(or bear’s lair), a shelter, sometimes burrowlike, in which a hibernating bear spends the cold winter months. The den’s layout and the length of the bear’s stay in it varies among different species and different parts of a given species’ area of distribution. The polar bear’s (Ursus maritimus) den is a vast, closed chamber in the thick of the snow on land (animals do not sleep on ice in the ocean), with an opening that is frequently covered by snow. Early in the winter, the bear digs a hole on the slope of a snowdrift. The animal is subsequently covered by a thick layer of snow. Only the pregnant females sleep in the dens, where they also give birth. Eurasian brown bears (U. arctos) make dens under fallen trees, the undersides of roots, in piles of brushwood, sometimes on the sites of old woodpiles, and even out in the open—in small holes that are covered by snow with only small openings remaining which are thawed by the animals’ breathing. Dens are located by these openings and the hoarfrost around them. In unforested mountains, bears usually make their dens below overhanging cliffs, under large rocks, and the like. Sometimes dens have beddings of leaves or moss. Asiatic black bears (U. thibetanus), which inhabit the Ussuri region, usually sleep in the hollows of poplar, linden, or oak trees. The bears of southern Asia—the sloth bear and sun bear—do not hibernate or make dens.
V. G. GEPTNER