The black bear is a medium-sized bear native to North America. It is the continent's smallest and most widely distributed bear species. Black bears are omnivores, with their diets varying greatly depending on season and location.

The bears enter their dens in October and November, although in the southernmost areas of their range, only pregnant females and mothers with yearling cubs will enter hibernation. Prior to that time, they can put on up to 14 kg (30 lb) of body fat to get them through the several months during which they fast. Hibernation in black bears typically lasts 3–8 months, depending on regional climate.

Hibernating black bears spend their time in hollowed-out dens in tree cavities, under logs or rocks, in banks, caves, or culverts and in shallow depressions. Although naturally-made dens are occasionally used, most dens are dug out by the bear itself. Females have been shown to be pickier in their choice of dens in comparison to males.

During their time in hibernation, a black bear's heart rate drops from 40–50 beats per minute to 8 beats per minute and the metabolic rate can drop to a quarter of the bear's (non-hibernating) basal metabolic rate (BMR). These reductions in metabolic rate and heart rate do not appear to decrease the bear's ability to heal injuries during hibernation.

The hibernating black bear does not display the same rate of muscle and bone atrophy relative to other nonhibernatory animals that are subject to long periods of inactivity due to ailment or old age. A hibernating black bear loses approximately half the muscular strength compared to that of a well-nourished, inactive human. The bear's bone mass does not change in geometry or mineral composition during hibernation, which implies that the bear's conservation of bone mass during hibernation is due to a biological mechanism. During hibernation black bears retain all excretory waste, leading to the development of a hardened mass of fecal material in the colon known as a A special hormone, leptin, is released into the bear's systems to suppress appetite. The retention of waste during hibernation (specifically in minerals such as calcium) may play a role in the bear's resistance to atrophy.

The body temperature of the black bear does not drop significantly, like other mammalian hibernators (staying around 35 °C (95 °F)) and they remain somewhat alert and active. If the winter is mild enough, they may wake up and forage for food. Females also give birth in February and nurture their cubs until the snow melts. During winter,  black bears consume 25–40% of their body weight. The footpads peel off while they sleep, making room for new tissue.

Many of the physiological changes a black bear exhibits during hibernation are retained slightly post-hibernation. Upon exiting hibernation, bears retain a reduced heart rate and basal metabolic rate. The metabolic rate of a hibernating bear will remain at a reduced level for up to 21 days after hibernation. After emerging from their winter dens in spring, they wander their home ranges for two weeks so that their metabolism accustoms itself to the activity. In mountainous areas, they seek southerly slopes at lower elevations for forage and move to northerly and easterly slopes at higher elevations as summer progresses.