Winterruhe

Winterruhe, literally “winter rest” in German, is a seasonal state of reduced activity and metabolism observed in some mammals during winter. The term encompasses a range of physiological strategies from deep hibernation to lighter torpor, sometimes described as winter sleep. In hibernators, body temperature can fall dramatically and metabolic rate drops to a fraction of normal; in less deep forms, such as in bears, the metabolic suppression is more modest.

Physiology: During Winterruhe, energy needs fall as activity, heart rate, and respiration slow. Animals rely on stored fat and may periodically arouse to drink, urinate, or adjust their position. The depth and duration of Winterruhe depend on species, climate, and food availability and can last from several weeks to several months.

Species: Hedgehogs, dormice, and many bats, as well as some ground squirrels, undergo true hibernation or extended torpor during winter. Brown bears and some other large mammals enter a form of winter sleep with less extreme temperature reduction. The exact patterns vary widely.

Triggers and ecology: Photoperiod, temperature, and food scarcity interact with internal circannual rhythms to initiate Winterruhe. The strategy reduces energy expenditure during months when food is scarce and conditions are harsh. Climate change and habitat changes can affect timing and success of these cycles.