Hyperphagia describes eating unusually large amounts before hibernation to build fat reserves.
The word refers to a short-term surge in food intake. Animals preparing for winter use this period to accumulate body fat, which becomes an internal energy store when food is unavailable and activity is greatly reduced. Ground squirrels and bears are familiar examples, although the exact timing and intensity vary by species.
Hyperphagia is not the same as thermogenesis, which is the production of heat, or gluconeogenesis, which is the biochemical creation of glucose from non-carbohydrate sources. Photoperiodism instead describes biological responses to changing day length, a cue that can help animals time seasonal behaviors.
Not every hibernating animal relies primarily on fattening. Some small species cache food rather than carrying large fat reserves, while others combine food storage with increased eating. During hibernation, stored fat supplies energy for basic metabolism and for periodic arousals, when body temperature and physiological activity temporarily return toward normal.