Most cubs stay with their mothers for 3 years. Bears that have recently left their mothers, at ages 3-5, have a high mortality rate as they face the world on their own. Kodiak bears become sexually mature at age 5 and can continue to produce cubs throughout their lives. The average interval between litters is about 4 years. Kodiak bears begin entering their dens in late October.
Pregnant sows are the first to go to dens, males are the last.
Males begin emerging from their dens in early April, while sows with new cubs may stay in dens until late June. Some males may forego denning, staying awake all winter. Researchers from NASA and the medical professions are very interested in denning physiology. They are trying to figure out how bears can sleep for up to 8 months without eating, drinking, urinating or defecating, yet when they awaken they have lost little bone mass or muscle tone and have no signs of uremia. Understanding this could help astronauts during extended space flights or patients who are bedridden.