Hyperphagia means a significant increase in appetite. And that is exactly what begins to happen to black bears this time of year. Bears are in “eat mode” through fall, and sometimes even into winter, so they can put on extra weight, up to 2-3 lbs. a day, to get ready for denning season. Hyperphagia is a behavior adapted by some bear species, including black bears, to combat a decline in natural food availability in the colder months.