It is thought this helps prevent pressure sores from developing. Bears also shift positions to better conserve heat. If food is present a bear does not have to hibernate, unless it is pregnant or winter conditions are severe enough such as found in Alaska. The den is a safe environment for the cubs as they grow.
Bear cubs are classified as altricial young rather than precocial, which means they need considerable parental care before they are able to leave the den. Not all bears hibernate, but in Alaska, most bears do, including the males. It is not uncommon for male polar bears and polar bears that are not pregnant or with young to remain active through periods of low food availability.
Bears in zoos will not hibernate if food is available, though they will slow down and sleep more than usual. Some zoo bears are fed year round, and do not hibernate. Since they do not undergo a winter weight loss like wild bears, some zoo bears can get very overweight, which is very unhealthy. Major den excavation is completed in days during which a bear may move up to a ton of material Brown ; Craighead and Craighead After completion of a den which consists of an entrance, a short tunnel, and a chamber bears will cover the chamber floor with bedding material ranging from spruce boughs to duff.
The bedding material has many air pockets which trap body heat and form a microclimate around the bear helping to keep it warm Craighead and Craighead These bedding materials are related to availability at the den site and not on the bears preference Judd et al. The den entrance is usually just large enough for the bear to squeeze through.
This minimal opening size helps prevent heat loss during hibernation since a smaller opening will be covered with snow more quickly than a large opening. In some dens the tunnel is dug straight into a hillside or at a slightly upward angle, an energy efficient design that reduces heat loss from the den chamber. However, some dens are not energy efficient and have tunnels dug at a downward angle which allows heat to escape through the den entrance. In most dens, the chamber is dug only slightly larger than the bear allowing for efficient heat retention.
However in some natural cavities used as dens, the chamber is much larger than the bear. Males and females with young usually dig the largest dens.
Movement to dens is correlated to weather and snow conditions with most movement usually occurring from late October to mid November Judd et al. However, Craighead and Craighead found hibernation onset varied by as much as one month depending on weather conditions. Latitude also influences den entrance, with bears in northern latitudes denning earlier and longer than bears in southern latitudes Haroldson et al.
Bears will remain in the area of their den for a few weeks and enter a state of lethargy during which they eat nothing and sleep frequently Craighead and Craighead According to Craighead and Craighead and Servheen and Klaver , final den entry occurs during severe snowstorms. In theory the fresh snow will hide any tracks or other evidence of where the bear's den is located. Pregnant females usually enter dens first, followed by females with young, subadults, and lastly, adult males Haroldson et al.
Grizzly and black bears breed from May through July but embryonic implantation does not occur until around December, about one month after solitary females den. The cubs are born in late January or early February and are naked, blind, and helpless Rogers They measure only about 8 inches 20 cm long and weigh from 8 - 12 ounces - g.
The newborn cubs do not hibernate. They sleep next to their mother, nurse, and grow rapidly. When black bear cubs emerge from the den at about three months of age, they weigh about 4 - 8 pounds 1. At ten weeks of age, grizzly bear cubs weigh 10 - 20 pounds 4. When temperatures warm up and food is available in the form of winter-killed ungulates or early spring vegetation, bears emerge from their dens.
Males, subadults, solitary females, and females with yearlings or two-year-olds usually leave the vicinity of their den within a week of emergence while females with new-born cubs remain in the general vicinity of the den for several more weeks Lindzey and Meslow , Haroldson et al.
Several physiological processes bears undergo during hibernation are of interest to medical researchers. When bears are hibernating and metabolizing body fat, their cholesterol levels are twice as high as during the summer and twice as high as the cholesterol levels of most humans Baggett Bears, however, do not suffer from hardening of the arteries arteriosclerosis or gallstones, conditions which result from high levels of cholesterol in humans.
The bear's liver secretes a substance that dissolves gallstones in humans without surgery. Category: Wildlife. Animals have developed many strategies to survive the winter, a time when food and water are scarce.
Some migrate to areas less effected by cold, some resist or adapt to withstand the effect of winter events, growing a thicker coat of fur for example. The snowshoe hare takes it even further, their thicker winter coat matches the color of snow, an adaptation known as camouflage. Other animals settle in for a long winters nap.
When we think about strategies animals use to survive the winter, we often picture birds flying south and bears hibernating in caves. However, not many animals truly hibernate, and bears are among those that do not. Bears enter a lighter state of sleep called torpor. Hibernation is a voluntary state an animal enters to conserve energy, when food is scarce, and minimize exposure to the winter elements. During hibernation an animal lowers its body temperature, slows its breathing rate, heart rate, and metabolic rate-the rate its body uses energy.
Typically, National Parks and local municipalities keep track of regular bear schedules and can advise the public when bears usually become active in their area. If these patterns are drastically changing, local populations may not be aware. This is unsafe for both parties: the humans and the bears. Bears can also come out of hibernation if they are disturbed. As previously mentioned, unlike other animals, bears do not slowly awaken from hibernation.
So, if disturbed by loud noises or approaching danger, they can immediately wake up to defend themselves or their cubs. Phone: How Long Do Bears Hibernate? What is Hibernation? Do Bears Hibernate? How Long Do Bears Hibernate Different species of bears hibernate for slightly different lengths of time, based mostly on their climate.
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