American black bear

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The American black bear (Ursus americanus) is a medium-sized bear native to North America. It is the continent's smallest and most widely distributed bear species. The American black bear is the world's most common bear species.

Black bear anatomy includes a straight face and flat shoulders. It has ears that are often pointed and a short tail. Length is 4 to 7 feet long. The skulls (9 to 14 in) of American black bears are broad, with narrow muzzles and large jaw hinges. Females tend to have more slender and pointed faces than males.

The ears are small and rounded, often pointed, and are set well back on the head. The vestigal tail is usually 5 inches long. The fur is soft, with dense underfur and long, coarse, thick guard hairs. Despite their name, black bears show a great deal of color variation. Individual coat colors can range from white, blond, cinnamon, or light brown to dark chocolate brown, bluish tint, jet black and albino. American black bears may develop a white “crescent moon” mark on the chest. Some may be mistaken for grizzly bears. Grizzly bears can be distinguished by their shoulder hump, larger size and broader, more concave skull.

The claws black or grayish brown, are short and rounded, thick at the base and tapering to a point. Claws from both hind and front legs are almost identical in length, though the foreclaws tend to be more sharply curved. The paws (5 to 9 in), being proportionly larger than other medium-sized bear species but much smaller than the paws of large adult brown and especially polar bears. The soles of the feet are black or brownish, and are naked, leathery and deeply wrinkled.

Black bear paws have short claws to help them climb, dig, gather plant food, and attack small mammals. They use their claws like fingers when they eat. Their front footprints have an oval base with a curved toe line. Hind tracks have a triangular indentation. Toes are spread out. Depending on the ground surface their claws may not be visible making specie information more difficult. This is particularly true in soils that have a fair amount of sand such as grounds near lakes and rivers where they hunt for fish. Black bear cubs leave small prints with no claw indentations.

Black bear weight tends to vary according to age, sex, health, and season. Seasonal variation in weight is very pronounced: in autumn, their pre-den weight tends to be 30% higher than in spring, when black bears emerge from their dens. Adult males typically weigh between 57–250 kg (130–600 lb), but can get as large as 1000 lb. Females weigh 33% less at 41–170 kg (90–370 lb).

A Black Bear has excelent eyesight and sense of hearing. Their keenest sense is the sense of smell, which is about seven times greater than a dogs. In his Great Bear Almanac, Gary Brown lists 20 different sounds in eight different contexts. Sounds expressing aggression include growls, woofs, snorts, bellows and roars. Sounds expressing contentment include mumbles, squeaks and pants.

Habitat

Solitary animals, black bears roam large territories, though they do not protect them from other bears. Males might wander a 15-80 sq. mile home range. Throughout their range, habitats preferred by American Black Bears have a few shared characteristics. They are often found in areas with relatively inaccessible terrain, thick understory vegetation and large quantities of edible material. Prime habitat consists of a forest canopy of hardwoods such as beech, maple, and birch, and coniferous species. Small, thick swampy areas provide excellent refuge cover.

When winter arrives, black bears spend the season dormant in their dens, feeding on body fat they have built up by eating ravenously all summer and fall. They make their dens in caves, burrows, brush piles, or other sheltered spots—sometimes even in tree holes high above the ground. Black bears den for various lengths of time depending on the climate in which they live, from Canada to northern Mexico.

Diet

Black bears are omnivores with their diets varying greatly depending on season and location. Most of their diet consists of grasses, roots, berries, and insects. They also eat fish and mammals—including carrion—and easily develop a taste for human foods and garbage.

Up to 85% of the black bear's diet consists of vegetation, though they tend to dig less than brown bears, eating far fewer roots, bulbs, corms and tubers than the latter species. When initially emerging from hibernation, they will seek to feed on carrion from winter-killed animals and newborn ungulates. As the spring temperature warms, black bears seek new shoots of many plant species, especially new grasses, wetland plants and forbs.

Young shoots and buds from trees and shrubs during the spring period are also especially important to black bears emerging from hibernation, as they assist in rebuilding muscle and strengthening the skeleton and are often the only digestible foods available at that time. During summer, the diet is comprised largely by fruits, especially berries and soft masts such as buds and drupes.

During the autumn hyperphagia, feeding becomes pretty much the full-time task of black bears. Hard masts become the most important part of the black bear's diet in autumn and may even partially dictate the species distribution. Favored masts such as hazlenuts, oak acorns and whitebark pine nuts may be consumed by the hundreds each day by a single black bear during fall.

During the fall period, American black bears may also habitually raid the nut caches of tree squirrels. Also extremely important in fall are berries such as huckleberries and buffalo berries. Black bears living in areas near human settlements or around a considerable influx of recreational human activity often come to rely on foods inadvertently provided by humans, especially during summertime. These include refuse, birdseed, agricultural products and honey from apiaries.

The majority of the black bear's animal diet consists of insects such as bees, yellow jackets, ants and their larvae. Black bears are also fond of honey, and will gnaw through trees if hives are too deeply set into the trunks for them to reach them with their paws. Once the hive is breached, black bears will scrape the honeycombs together with their paws and eat them, regardless of stings from the bees.

Black bears will fish for salmon during the night, as their black fur is easily spotted by salmon in the daytime. Other fish including suckers, trout and catfish are readily caught when possible. Although black bears do not often engage in active predation of other large animals for much of the year, the species will also regularly prey on mule and white-tailed deer fawns in spring given the opportunity. In addition they have been recorded similarly preying on elk and moose calves. Corn crops and oak-hickory mast are also common sources of food.

Black bear predation on adult deer is rare but has been recorded. They may even hunt prey up to the size of adult moose, which are considerably larger than themselves, by ambushing them. In Labrador, black bears are exceptionally carnivorous, living largely off of caribou, usually sickly, young or dead specimens, and rodents such as voles. This is believed to be due to a paucity of edible plant life in this sub-Arctic region and a local lack of competing large carnivores (including other bear species).

Like brown bears, black bears try to use surprise to ambush their prey and target the sickly animals in herds. Once a deer fawn is captured, it is frequently torn apart alive while feeding. If able to capture a mother deer in spring, the bear frequently begins feeding on the udder of lactating females, but generally prefer meat from the viscera.

Black bears often drag their prey to cover, preferring to feed in seclusion. The skin of large prey is stripped back and turned inside out with the skeleton usually left largely intact. Unlike wolves and coyotes, black bears rarely scatter the remains of their kills. Vegetation around the carcass is usually matted down by black bears and their droppings are frequently found nearby.

Black bears may attempt to cover remains of larger carcasses, though they do not do so with the same frequency as cougars and grizzly bears. They will readily consume eggs and nestlings of various birds and can easily access many tree nests, even the huge nest of the bald eagle. Black bears have been reported stealing deer and other animals from human hunters.

Behavior

Black bears are highly dexterous, being capable of opening screw-top jars and manipulating door latches. They also have great physical strength. Even bear cubs have been known to turn over flat-shaped rocks weighing 310 to 325 pounds by flipping them over with a single foreleg. They move in a rhythmic, surefooted way and can run at speeds of 25–30 mph.

Black bears have good eyesight, and have been proven experimentally to be able to learn visual discrimination tasks based on color faster than chimpanzees and as fast as dogs. They are also capable of rapidly learning to distinguish different shapes, such as small triangles, circles and squares.

American black bears tend to be territorial and non-gregarious in nature. However, at abundant food sources (i.e. spawning salmon or garbage dumps) black bears may congregate and dominance hierarchies form, with the largest, most powerful males dominating the most fruitful feeding spots. They mark their territories by rubbing their bodies against trees and clawing at the bark.

One of the more notable facts about this species is that they are excellent climbers, even when cubs. Black bears are excellent and strong swimmers, doing so for pleasure and to feed (largely on fish). Black bears climb regularly to feed, escape enemies or to hibernate. Black bears may be active at any time of the day or night, although mainly forage by night.

The black bear is very adaptable. They are quite intelligent and curious. But this smaller bear is very shy and generally avoids confrontations. Records of human attacks are rare.

North American Black bears like to swim. If there is water where they live they will exploit it for food. Since bears like to hunt fish they are not shy of water. In fact their baby cubs take to the water quickly. In their search for food in their habitat they can cross ponds, lakes, and rivers to get to better feeding grounds (including campgrounds, lodges, and resorts). They use their powerful front and hind legs to paddle swiftly through water and are actually graceful swimmers.

At its normal pace black bears waddle slowly and casually. When in danger or hunting for prey they have the ability to burst into running mode with speeds up to 25 to 30mph. They can run for short distances only.

Hibernation

Black bears enter their dens in October and November. Prior to that time, they can put on up to 30 pounds of body fat to get them through the seven months during which they fast. Hibernation in black bears typically lasts 3–5 months. During this time, their heart rate drops from 40–50 beats per minute to 8 beats per minute.

They spend their time in hollowed-out dens in tree cavities, under logs or rocks, in banks, caves, or culverts, and in shallow depressions. Females, however, have been shown to be pickier in their choice of dens, in comparison to males. Although naturally-made dens are occasionally used, most dens are dug out by the bear itself.

A special hormone, leptin is released into the black bear's systems, to suppress appetite. Because they do not urinate or defecate during dormancy, the nitrogen waste from the bear's body is biochemically recycled back into their proteins. This also serves the purpose of preventing muscle loss, as the process uses the waste products to build muscle during the long periods of inactivity. In comparison to true hibernators, their body temperature does not drop significantly (staying around 35 degrees Celsius) and they remain somewhat alert and active.

If the winter is mild enough, they may wake up and forage for food. Females also give birth in February and nurture their cubs until the snow melts.

During winter, black bears consume 25–40% of their body weight. The footpads peel off while they sleep, making room for new tissue. In the most southernly areas only pregnant females and mothers with yearling cubs will enter hibernation.

After emerging from their winter dens in spring, they wander their home ranges for two weeks so that their metabolism accustoms itself to the activity. In mountainous areas, they seek southerly slopes at lower elevations for forage and move to northerly and easterly slopes at higher elevations as summer progresses.

Black bears use dense cover for hiding and thermal protection, as well as for bedding. Black bears were once not considered true or "deep" hibernators, but because of discoveries about the metabolic changes that allow black bears to remain dormant for months without eating, drinking, urinating, or defecating, most biologists have redefined mammalian hibernation as "specialized, seasonal reduction in metabolism concurrent with scarce food and cold weather". Black bears are now considered highly efficient hibernators.

Reproduction

Sows usually produce their first litter at the age of 3–5 years. Sows living in more developed areas tend to get pregnant at younger ages. The breeding period usually occurs in the June–July period, though it can extend to August in the species' northern range. The breeding period lasts for 2–3 weeks. Both sexes are promiscuous. Males try to mate with several females but large, dominant ones may violently claim a female if another mature male comes near. Sows tend to be short tempered with their mates after copulating.

The fertilized eggs undergo delayed development and do not implant in the female’s womb until November. The gestation period lasts 235 days, and litters are usually born in late January to early February. Litter size is between one and six cubs; typically two or three.

At birth, cubs weigh less than a pound. They are born with fine, gray, downlike hair, and their hind quarters are underdeveloped. They typically open their eyes after 28–40 days, and begin walking after 5 weeks. Cubs are dependent on their mother's milk for 30 weeks, and will reach independence at 16–18 months. At the age of six weeks, they attain 2 lb, by 8 weeks they reach 5 lb and by the age of 6 months they weigh 40 to 60 lbs. They reach sexual maturity at the age of three years, and attain their full growth at 5 years.

The average lifespan in the wild is 18 years, though it is quite possible for wild specimens to survive for more than 23 years. In Minnesota, 99% of wintering adult bears were able to survive the hibernation cycle in one study.

With the exception of the rare confrontation with an adult brown bear or gray wolf pack, adult black bears are not usually subject to natural predation. Black bear cubs tend to be more vulnerable to predation than adults. Known predators of bear cubs have included bobcats, coyotes, cougars, wolves, brown bears and other bears of their own species. Many of these will stealthily snatch small cubs right from under the sleeping mother. There is a single record of a golden eagle snatching a yearling cub. Once out of hibernation, mother bears may be able to fight off most potential predators. Even cougars will be displaced by an angry mother bear if they are discovered stalking the cubs. Flooding of dens after birth may also occasionally kill newborn cubs.

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