If enough food can't be found to prepare for hibernation, it can be delayed. Another option is to eat a large amount of food starting in late summer, building up a reserve of internal fat. Food can be kept in the den if it's nonperishable, but this requires the animal to wake up briefly during the winter to eat.
Bats are well-known for wintering in caves or attics. Other bears might spend the winter in a hollow beside a tree or a shallow cave, leaving them partly exposed to the weather. Some animals prepare a den (also known as a hibernacula) and line it with insulating material, just as leaves or mud. Preparation is required to hibernate successfully. Animals that go into daily torpor depend instead on circadian rhythms, the daily version. These circannual rhythms aren't fully understood, but all animals are affected by them, even humans. Experiments under these conditions have proven that some species will automatically enter hibernation at the appropriate time, guided by an internal biological "calendar".
When an animal awakes from hibernation, it exhibits many signs of sleep deprivation and needs to sleep a lot over the next few days to recover.Įven if an animal has no idea what the outside temperature is, how early the sun is setting or the current state of food supplies, many would still enter a hibernation state around the same time each year. In fact, the brain waves of hibernating animals closely resemble their wakeful brain wave patterns, though they're somewhat suppressed. Sleep is primarily characterized by changes in brain activity. Sleep is also pretty easy to break out of - if you're awakened from even your deepest sleep, you can be fully awake within several minutes. There are physiological aspects of sleep that are similar to hibernation, such as a reduced heart and breathing rate and lowered body temperature, but these changes are very slight compared to hibernation. Sleep, by contrast, is a mostly mental change. We'll get into the details shortly, but for now it's sufficient to say that a hibernating animal's vital signs are very different from the vital signs of an awake animal. The most significant element of hibernation is a drop in body temperature, sometimes as much as 63 degrees F. These animals aren't just sleeping, they're undergoing physiological changes that can be very drastic. So is hibernation basically a really long nap? No. It differs from mammalian hibernation because reptiles are cold-blooded - they can't control their own body temperature, so they need to spend the winter in a place that will stay warm enough. Hibernation in reptiles is sometimes called brumation. When an animal enters a hibernationlike state during the summer, it's known as estivation.
For the purposes of this article, we'll use the term hibernation to describe any long-term reduction in body temperature ( hypothermia) and metabolism during winter months. Not everyone accepts this narrow definition, however. By this definition, bears don't hibernate, because their body temperature drops only slightly and they awake relatively easily. A common definition of hibernation is a long-term state in which body temperature is significantly decreased, metabolism slows drastically and the animal enters a comalike condition that takes some time to recover from.
MIGRATE AND HIBERNATE ANIMALS HOW TO
Mark Raycroft/Minden Pictures/ Getty Imagesīiologists love to argue about how to classify things, and hibernation is no different. On the next page, we'll discuss how hibernation is different from sleep - and learn what happens to animals in the zoo. Certain birds and bats enter a sort of daily hibernation called torpor. Some fish can hibernate in a waterproof mucus envelope if their lake dries up. Many animals hibernate in a den all winter, but some animals hibernate in the summer. Hibernation is more varied than you might think. Larger animals are less apt to hibernate because of the additional energy required to warm up a large body. Smaller animals tend to be more likely to hibernate, because migration would require an enormous amount of energy relative to their body size. Whether an animal hibernates or migrates to a warmer area is generally a quirk of evolution.
All of these things happen so the animal can use less energy. They stop eating and in many cases stop excreting. Some animals enter a state of "suspended animation." Their breathing and heart rates slow and they allow their body temperature to drop, in some cases even below freezing. There are many winter survival strategies in the animal world, and one of the most fascinating is hibernation. But what happens when winter comes and it becomes very difficult to find food? How do animals survive with few energy sources available? The system works fine when there's plenty of fruit on the trees or rabbits to catch and eat (or pizzas in the freezer). That's the whole reason animals eat - to gain enough energy to fuel all those processes.
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