Kingdom:  Animalia
Phylum:  Chordata
Class:  Mammalia
Order:  Carnivora
Family:  Ursidae

    We have included bears in two sections:  hibernation and torpor.  This was the first time that we ever did research and found out that different books might have different information that doesn't agree about the same subject.  
    Most books say that bears are not "true" hibernators.  This is because they:

    Bears live in forests, swamps, and mountains.  They live in the Arctic, North America, South America, Europe, and Asia.   Wild bears [not in zoos] live about 15-30 years.  They live longer in zoos.  
   Bears are omnivores which means they eat plants and animals.  They try to stay away from people.  They will attack any person or animal who threatens them, their cubs, or their dens.  Unless they have cubs, bears usually live alone and don't travel around in groups.  Black bears will eat all kinds of things, from dead animals to grass, roots, and berries.  
   Bears do sleep a lot of the winter but their body temperatures don't drop very much.  This is how the female can take care of her cubs that are born during winter.  True hibernators take a long time to wake up from their winter sleep but bears are alert and know what is going on around them.  They can get up right away. 
    In the fall, bears start to look for a winter den.  This den will be safe and somewhere that the bear doesn't go at other times of the year.  Bears like to make their dens in caves, hollow trees, banks of creeks or even big pipes.  Brown bears always dig holes for dens.  Sometimes they even dig tunnels to the den. 
    When they make their den, they drag in leaves and tree branches for a bed.  The den will be big enough for the bear to move around and stretch but small enough that the bear's body heat warms it.  When it begins to snow, they crawl inside to sleep.  The snow will lay over the den and help to hold the bear's body heat inside.
   Males mate with the females and then leave them to find shelter.   Bears can be pregnant for three to eight and a half months.  Different kinds of bears will have different lengths of time.  The mother bear [sow] will have between one and four cubs during hibernation.  The sow will have only one litter a year and this litter can be born anytime between October and March.  The cubs are very small.  They weigh from 7-25 ounces each.  Some weigh less than a pound of butter.  Cubs are born hairless.  They stay with their mother two years and she teaches them to hunt and take care of themselves.
   During hibernation, a bear's eyes will be open when it is awake but it might be groggy.  Its body gets a little cooler but not as cold as other hibernating animals.  Since it mostly sleeps and lays around, the body fat that it stored in the summer and fall lasts longer.  It doesn't take too much body fuel to sleep.  Its body does lots of things while it is in hibernation.  It makes its own water and recycles wastes.  Bears won't drink or get rid of wastes for a few months.  They will lose about eight pounds a week during hibernation or torpor.  The weight they lose will be from stored fat and not muscle.  This means that when they leave the den in the spring, they are still strong.   In Spring, they will wake up and leave the den.  They will be thinner and very hungry.
   Here's something interesting.  Bears don't get rid of wastes--or go to the bathroom--for a few months.  The urine is broken down inside their bodies and reused as protein to help the bear keep its muscles healthy.  A 'plug' of feces, hair, and nest stuff forms at the end of the bear's digestive tract.  This comes out when the bear leaves the den and goes to the bathroom.  Disgusting, but interesting.
   Polar bears can go into hibernation at any time of the year.  They will do it if they can't find food.  This allows them to adapt to having no food.  Most polar bears don't hibernate but some pregnant females will.  They make their dens in the fall, give birth during the winter, and stay there until spring.  The temperature inside the den can get 40 degrees hotter than the air outside just because of the bear's body heat.
    Bears aren't like birds that migrate, or move away from bad weather.  They won't leave their area to find a warmer place.  They adapt to the climate around them by sleeping through the cold season.    Scientists disagree on whether bears hibernate, but all think they do go into a torpor.   Torpor is a sleep where the animal is a little alert but kind of drowsy or sluggish.