Some animals in cold climates escape the severest weather by hibernating. That is, they spend the winter months in a very long deep sleep. The world hibernate comes from the Latin hibernare, which means to winter many animals find sheltered place underground or at the base of trees and hedges in which to hibernate.
Hibernating animals include frogs, newts, toads, lizards, dormice, bats, snails, tortoises, hedgehogs, and squirrels. During hibernation animal appears to be lifeless. Breathing almost stops and the heartbeat is slow. The feet, tails and snouts of warm-blooded animals are much colder than usual, although the blood in their hearts remains at a high temperature. The animals are nourished by sugars stored in the liver and by the fat that has been built up during the summer.
Mild winters are bad for hibernating animals, because they wake up during warm spells, and use energy in moving about. But they do not feed normally and by the end of the winter, are very thin.
Creatures, which cannot burrow find cracks and holes in which to shelter. Some have been known to return to same place year after year. Just as animal in cold climates escape winter by hibernating, so some in the tropics avoid hot, dry spells by sleeping underground. This is known as aestivation, derived from the Latin word meaning heat.