We have our homes with heating and cooling systems to help us cope with temperature extremes, but how do wild animals survive? Hibernation or “winter sleep” is the state of inactivity or low metabolic process animals perform during winter. Aestivation or “summer sleep” is the low metabolic process animals use to cope through hot dry summers.
Photo credit: Moira Rosser
During hibernation, an animal appears to be dead and its heart rate and body temperature and movements slow down. True hibernators are the jumping mouse, little brown bat, the eastern chipmunk, some species of ground squirrels, and a bird called the grey and white poorwill. Hibernators have regular white fat and special brown fat. The brown fat around the animal’s brain, heart and lungs sends a quick burst of energy to the vital organs telling it when it’s time to wake up.
Bears do not hibernate but rather go into torpor. Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Bears, raccoons, and skunks are all "light hibernators" that use torpor to survive the winter. Bears are especially unique as they do not eat, drink, urinate or defecate for up to six months during their winter sleep.
The main difference between hibernation and torpor is during torpor, the animal is able to wake up quickly to avoid danger, or if there is an opportunity to feed.
Another type of hibernation is when an animal or bird becomes dormant daily to conserve energy. They may not have consumed enough food to get through the day, so they just shut down. Hummingbirds and the little brown bat use this adaptation.
Hummingbirds like this little beauty go dormant daily to conserve energy
Brumation is another form of becoming dormant, and is similar to hibernation, but for reptiles and amphibians. Ectothermic or “cold-blooded” animals like fish, frogs, snakes and turtles burrow themselves in the mud or under leaves and rocks in the winter. Insects find shelter in holes in the ground, under the bark of trees or inside rotting logs. Some insects create homes for themselves in plants, by making the plant form a small lump or "gall". The gall becomes the insect’s home and food source.
In summer, aestivation is a dormant state that some animals assume during hot, dry periods. Animals that hibernate are protected from the cold, while animals that aestivate are protected from dryness. The animal’s body functions slow down as in hibernation, allowing it to survive hot dry periods.
Photo credit: Moira Rosser
Similar to hibernation and torpor, aestivation is characterized by a period of inactivity and a lowered metabolic rate. Many animals, both invertebrates and vertebrates, use this tactic to stay cool and prevent desiccation when temperatures are high and water levels are low. Animals that aestivate include mollusks, crabs, crocodiles, some salamanders, mosquitoes, desert tortoises, the dwarf lemur, and some hedgehogs.
Northern ground squirrels prepare themselves for the outset of hibernation while ground squirrels living in the desert will aestivate in their burrows.
Amphibians, reptiles, insects, snails and fish will aestivate. Various kinds of frogs, lungfish and salamanders form a cocoon before entering aestivation to prevent water loss from their skin. When water reappears in its environment, the reptile or fish awakens from its sleep.
These coping strategies enable animals to survive weather extremes. You can learn more about wild animals, by visiting the North Island Wildlife Recovery (NIWRA) centre.
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