A wintry walk is an ideal time to reflect on past seasons and the many marvels of nature. But as we stroll amidst frosted forests, powdery peaks, and icy ponds, many of us forget that one of the most critical stages of life is quietly occurring just beneath our feet, below the surface of the water, under a rock, or within a hollow log.
In this issue of Leaf Litter, we will explore the fascinating world of species hibernation and seasonal dormancy. All types of deep “sleep,” including hibernation, estivation (aestivation) and diapause, serve as critical stages in the lives of many species–stages that should not be forgotten as we strive to conserve biodiversity.
There are many definitions of hibernation, but generally, the term refers to a state of regulated hypothermia that allows an animal to conserve energy and survive during the winter when there is a lack of food. During hibernation, an animal’s metabolism slows down significantly, its body temperature lowers, and it does not eat, drink, urinate or defecate. Some hibernating animals stir as often as once a week, but others sleep throughout the season. Examples of hibernating animals include: bats, ground squirrels, terrapins, snakes, frogs, marmots, and newts. There is even a rare bird, the Poorwill, which hibernates.
There is debate about whether or not the bear is a true hibernator, since its body temperature does not decrease as dramatically as other hibernating animals. If you ask Minnesota Natural Resources Bear Biologist Dave Garshelis, as we did, he’ll tell you they are. Until recently, no primate and now tropical mammal was known to hibernate, but an article in the June 24 edition of Nature, reveals that the Madagascan fat-tailed dwarf lemur hibernates in tree holes for seven months.
Some animals, such as badgers, raccoons, skunks and chipmunks, have shorter hibernation times, sometimes referred to as torpor. Also used to describe very short periods of sleep or inactivity during the day or night, torpor involves a decrease in the animal’s heart rate and temperature. An animal in torpor does not seem to see, hear or feel things going on around it, and can be quite groggy upon waking. Many animals in hot, desert climates go into a state of dormancy to survive hot, dry conditions. As with hibernation, heartbeat and breathing are very slow. Estivating animals use significantly less energy, and they do not move, grow or eat during this time. Examples of animals that estivate include earthworms, snails, some frogs, toads and turtles, and many reptiles.
Many insects, including the Colorado potato beetle adapt to a lack of food or water by entering a sleep state known as diapause, where they do not grow. Some insects, including the gypsy moth, grasshopper, and white cabbage butterfly, lay diapausing eggs, which experience a pause in their cycle from egg to adult.