The den is commonly a brush pile. It may also be a pocket or cave in rocky ledges; a hollow in a large tree or a fallen log; a sheltered depression or cavity dug out at the base of a log, tree, or upturned root; or even a simple hole dug into a hillside. Male bears den up almost anywhere. Females, however, are more particular, selecting protected sites and lining them with stripped bark, leaves, grasses, ferns, or moss. Bears become mature at about three and a half years. Black bears give birth every other year.
The breeding season occurs during June and July. After mating, the fertilized egg does not become placed into the mother's uterus and grow until fall.
This process is called "delayed implantation. The female's ability to produce cubs relates directly to fall food supplies.
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If the food supplies are poor prior to denning, the female may not have enough fat reserves to grow a cub, and so no cubs will be born. Inadequate food supplies may also affect fetal development and cub survival. Well-nourished females are much more likely to produce healthier, larger cubs, and in greater numbers. Cubs are born in late January or early February while the mother is denning.
The number of cubs varies from one to five, but the average is two. The cubs, weigh only 8 to 10 ounces at birth, and are about the size of a chipmunk. The cubs will remain with the mother until they are about 16 months old. Young females may remain close to their mother's home range, but young males must find their own territory. Although the black bear belongs to the order Carnivora, it is a true omnivore, eating both plants and animals.
Major food sources include seeds and insects, but the black bear is an opportunist and will eat just about anything that crosses its path. Early spring is the most difficult time of the year for bears. At this time, food is scarce and bears must scavenge intensively to stay alive. Because wetlands green up first, wetland grasses and green, leafy plants have been found to be the primary food of the black bear in the spring.
However, these have limited nutritional value, so bears continue to draw from any remaining fat reserves. From the time they emerge from their dens to the end of July, their activities center around forested wetlands, beaver dams, and along streams and riverbanks. Typically, bears must wait until early to mid-summer before regaining an adequate level of nutrition.
By early summer, bears have the opportunity to eat a variety of succulent plants such as the roots of the jack-in-the-pulpit and berries that are beginning to become available. Bears may also prey upon young deer and moose at this time, although bears do not actively hunt for these food sources. During this time, no single food source is available in such abundance that bears can concentrate on only one item.
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As summer progresses, raspberries, blueberries, and blackberries ripen. If these crops are abundant, bears immerse themselves in a concentrated food source with high sugar content. By late August, bears seek foods with the highest nutritional value. In an effort to store as much energy as possible, they will eat up to 24 hours a day.
If beechnuts and acorns are plentiful, bears will move into productive beech and oak stands and consume high quantities of the nuts.
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Bears may travel many miles to reach fall food supplies and will continue to forage for beechnuts for several weeks. Other fall foods include cherries, apples, succulent plants, and berries. Bears will also eat available crops of corn and oats, and will commonly raid bee hives. In , the black bear was elevated to the status of a big game animal and received protection under Vermont's laws.
The techniques of black bear harvesting were further regulated by banning trapping in , controlling the use of hunting dogs, outlawing baiting, and prohibiting the shooting of bears at dumps in Because of improvements in habitat and through management efforts, Vermont's black bears have made a strong comeback. Their numbers are higher today than they have been in years. Close monitoring and management of Vermont's black bear population is necessary to ensure it remains healthy and abundant in the future.
The principle concern for their future relates to their habitat. Major concerns include development and varying production of their critical wild foods, such as acorns and beechnuts. By examining the sex and age from harvested bears each year, wildlife biologists are able to estimate the bear population in Vermont. Perhaps because black bears range widely—traveling when necessary well over miles outside their normal home ranges in search of food—they have evolved an astonishing ability to find their way home. While a graduate student at the University of Minnesota, bear expert Lynn Rogers reported that one pound male that found itself miles from its den in mid-October walked straight back to its den over nine consecutive nights.
Curiosity is often mistaken for aggression in black bears. Wayne Lockwood, M. The heaviest weight recorded for wild black bears is pounds for a male and pounds for a female. Those weights were measured at peak fall weight, however, and most black bears, especially after winter, weigh less than half that much.
While they may look ponderous at their fattest in the late fall, they can sprint up to 30 miles an hour when they have to and can climb trees with great facility. Under ideal conditions, black bears can live more than 30 years, though they usually die far younger, mostly from encounters with people. Preparations for over-wintering begin in the summer, when bears begin gorging carbohydrate-rich berries and other foods to put on weight.
During this period, they can gain as much as 30 pounds per week. In early autumn, a bear and its cubs, if any will rake leaves, twigs, and other plant materials into the den to form a nest. Throughout the fall its activity level steadily drops until it ends completely when the bear enters its den. Bears make dens in burrows, caves, hollowed-out trees, and rock crevices.
Dens of the bears Rogers studies in Minnesota typically feature entrances just large enough for a bear to squeeze through; interior chambers measure two-and-a-half to five feet wide and two to three feet high. Sometime in late fall, black bears receive an unidentified signal that it's time to bed down for the winter. Corbis Images. It's cramped for a single bear, much less for a mother and her cubs.
But that's the way bears like it: Black bears do no exercising of any sort during the winter months, preferring to lie rolled into a tight ball, with their heads between their forepaws and their heavily furred backs exposed to the worst of the cold. Dens themselves offer little insulation. Bears keep warm using their great bulk, their inches-deep layer of fat, and their fur, which more than doubles its insulative value during the fall.
These daintier creatures must awaken every few days, raise their body temperatures to summer levels, eat stored food, and pass waste. Bears can go on slumbering because their warm pelts and lower surface-to-mass ratio allow them to better retain body heat.maruthijournl.com/js/spyware/pytyx-what-app-to.php
This, in turn, enables them to cut their metabolic rate in half. Using telemetry, Edgar Folk of the University of Iowa monitored the heart rate of a captive bear in Alaska as it slept. In the early fall, its heart beat 40 to 50 times a minute for most of each night. By December, when the bear was deep in hibernation, its sleeping heart rate had slowed to as few as eight beats a minute. Hibernating black bears, particularly mothers with cubs, sleep lightly, and bear expert Roger Powell says he has never approached a den in which a resident bear was not watching him come.
Black bears keep their heads and torsos warm enough that they can wake if disturbed, though some may take awhile to do so. In a article in Natural History , Rogers told of the time he accidentally fell onto a six-year-old female in her den. Even though her cub bawled, she didn't wake up for at least eight minutes. On the other hand, some individuals can revive disconcertingly quickly. Rogers again:. On January 8, , I tried to hear the heartbeat of a soundly sleeping five-year-old female by pressing my ear against her chest.
I could hear nothing. Either the heart was beating so weakly that I could not hear it, or it was beating so slowly I didn't recognize it. After about two minutes, though, I suddenly heard a strong, rapid heartbeat. The bear was waking up. Within a few seconds she lifted her head as I tried to squeeze backward through the den entrance. Outside, I could still hear the heartbeat, which I timed after checking to make sure it wasn't my own at approximately beats per minute.
Over-wintering black bears do other extraordinary things—things that might someday benefit humans. For starters, snoozing bears are able to gain all the sustenance they need entirely from within their own bodies. Fat tissues break down and supply water and up to 4, calories a day; muscle and organ tissues break down and supply protein. Biologists are eagerly teasing physiological secrets out of hibernating black bears—secrets that may hold benefits for humans.
Our bodies do the same thing when we're starving—with one crucial difference: Our bodies can't restore muscle and organ tissue, which those of hibernating bears can. Bears' bodies are somehow able to take urea—a chief component of urine that is produced during tissue breakdown and that, if left to build up, becomes toxic—and use the nitrogen in it to build new protein.
Even though a hibernating bear drinks no water, it does not become dehydrated.
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In a study published in the American Journal of Physiology, hibernation expert Ralph Nelson and colleagues at the Mayo Clinic and Mayo Foundation found that the three hibernating bears they studied were in "almost perfect water balance" after about days of hibernation, during which they swallowed not a single drop of water.
Nelson's team and other researchers want to learn how bears accomplish this metabolic feat, during which the amount of urine entering the kidneys drops by 95 percent, in hopes of using the information to help treat people suffering from chronic kidney failure. Hibernating bears also have what would seem to be dangerously high cholesterol levels. Because they live off their own fat, their cholesterol levels are more than twice what they are in summer and more than two times higher than those of most people. But bears evince no signs of hardening of the arteries or the formation of cholesterol gallstones.
Research has shown that hibernating bears generate a form of bile acid that, when administered to people, dissolves gallstones, eliminating the need for surgery. Despite being cooped up in a space about the size of a doghouse, hibernating black bears also appear to avoid muscle cramping and degenerative bone loss. How they accomplish this remains a mystery.
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