Once snuggled in their winter den a bear may remain inside for up to 2 - 7 months without eating, drinking, urinating or defecating. Their unique metabolic system allows them to live off their fat reserves and reprocess internal waste products so they can keep sleeping. Female bears will give birth and nurse their cubs during this time of extended fasting, so building up fat reserves is extremely important. During hibernation a bear will burn up about 4,000 calories per day. Tropical bears that can feed throughout the year, such sun bears, sloth bears and spectacled bears and bears in zoos that are fed year-round, do not hibernate.
Bears usually construct day beds during spring and summer.
Tropical bears such as the spectacled bear may use day beds all year round as well as for birthing beds. Day beds are found near food sources and they are sometimes elevated to get a good view of the surrounding area. A day bed can be used for a long or short period of resting and they are often used after a heavy meal. Females and their cubs usually choose areas that are as high as possible so the they can detect any possible dangers. The American black bear sleeps stretched out in trees, or if it sleeps on the ground it prefers grassy areas or areas covered with conifer needles.