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Why do hibernating mammals build up body fat before winter?
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Dormancy
Virginia big-eared bats (Corynorhinus townsendii virginianushibernating) are true hibernators, entering a state close to death for much of the winter.
Hibernating mammals build up significant stores of body fat in the fall to survive the winter months when food sources become scarce. This accumulation of white and brown adipose tissue serves as a vital energy reserve during their period of dormancy.1
The fat stores fulfill two primary functions:
- Energy Source: Hibernation requires the mobilization of body resources to maintain a minimal metabolic level necessary for life. Because hibernators experience periodic arousals—which consume significantly more energy than the state of deep hibernation itself—these fat reserves provide the fuel required to sustain the animal through the winter and support recovery.21
- Heat Production: Brown adipose tissue is specialized for generating body heat through a process called nonshivering thermogenesis. This is particularly important for maintaining essential physiological functions and warming the animal when it wakes from its torpid state.31
By storing this energy, mammals can bypass the winter season entirely, emerging in the spring when food becomes more plentiful.1