Polar bear maternity dens are uniquely vulnerable to disturbance during the critical winter denning period when females give birth and nurse cubs.
Female polar bears in maternity dens are in a uniquely vulnerable physiological state - fasting for up to 6 months while nursing cubs that double in size weekly from maternal fat reserves. Disturbance that forces premature emergence exposes underdeveloped cubs to lethal cold and breaks the nursing bond at a critical development stage. The energy cost of stress arousal from disturbance depletes maternal reserves needed for cub survival. Even non-emergence disturbance that elevates maternal stress hormones may reduce milk production and cub growth during a period when every calorie is critical. Den protection is therefore both an individual welfare priority and a population management necessity given the slow reproductive rate of polar bears.