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How does body size affect how quickly an animal can enter hibernation?

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The image shows a group of Virginia big-eared bats sleeping upside down in a dark cavern. — Dormancy Virginia big-eared bats (*Corynorhinus townsendii virginianushibernating*) are true hibernators, entering a state close to death for much of the winter.

Body size is a significant factor in how quickly an animal can enter hibernation. Larger animals generally take longer to enter hibernation than smaller ones because heat must radiate from the body before the internal temperature can be lowered.1

For a large animal, the process of entering and emerging from hibernation would be metabolically extravagant. For example, a 200-kilogram (440-pound) bear would require a massive amount of energy to warm its body back to normal temperatures, equivalent to its entire 24-hour energy budget. Consequently, even if there were sufficient time in a day to complete these cycles, the energy expenditure would defeat the primary purpose of hibernation, which is to conserve resources.1

In contrast, smaller animals like hummingbirds and bats can enter and emerge from dormancy much more efficiently, as the metabolic cost of warming their smaller bodies is significantly lower.1