What is the term for the long-term winter torpor in mammals and birds?

The term for long-term winter torpor in mammals and birds is hibernation. It is a seasonal survival strategy in which an animal greatly reduces its metabolic rate and, usually, its body temperature to conserve energy when food is limited.

Hibernation is more complex than simply sleeping for an entire winter. Many hibernating mammals alternate deep torpor with brief arousals that restore body temperature and normal physiological activity. Before entering torpor, they typically build fat reserves that fuel them through the dormant period.

The word is often used broadly, but scientists distinguish hibernation from shorter daily torpor and from brumation, a winter slowdown associated mainly with ectothermic animals such as reptiles and amphibians. Estivation is a comparable response to hot or dry conditions rather than winter. Most birds do not truly hibernate, although the common poorwill is a well-known avian exception and some birds use shorter bouts of torpor.