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American Black Bear


Range and Habitat

The American black bear has a large range all over North America. It is found in most of southern Alaska, southwestern Canada, and many places in the USA except the great plains areas and the southeastern US, except parts of Florida and Georgia. Very small populations exist in northern Mexico.

The American black bear is typically found in densely forested mountainous terrain in elevations ranging from 900-3,000 m.

Physical Appearance

The American black bear is medium-sized, as bears go. The males are 20 - 60 % larger than the females. The largest black bear on record weighed 660 lb (300 kg). They are usually a uniform black, brown, or cinnamon color with a lighter colored muzzle. White individuals have been observed on the coast of British Columbia, but are rare. The hair is course and short to medium in length, and it is uniform in length all over the body, except for shorter hair on the muzzle and feet. Like all bears, the black bear is plantigrade, which means that it walks with its entire foot like a human, instead of on its toes like cats and dogs, which are digitigrade. They can also stand up in their hind legs for extended periods of time, which makes them look rather human. Bears also tend to sit down on their rear with their upper body off the ground, like a person, too.

They have a broad, pointed muzzle, which houses 42 teeth. Their body is large and rounded out, with short, thick legs. They have long claws, that can be several inches long, and cannot be retracted. Their short ears are round, and heavily lined with fur, and located near the sides of its head. They have a very short, stubby tail, just like all bears. Their nose is like a dog's nose, as they rely heavily on scent. Their sense of eyesight and hearing are relatively poor.

Diet

American black bears are omnivorous, but the majority of their diet is comprised of vegetation. Generally speaking, about 80% of their diet is comprised of grasses, herbs, berries, roots, fungus, fruits and nuts. Insects comprise another 10%, and the other 10% is human refuse. Where bears come into more contact with people, like around cities, garbage comprises a larger part of their diet. Black bears that live along the coast or near rivers often eat fish and crustaceans, as well as scavenging on marine mammal carcasses. In northern Canada, the bears there eat a lot of lemmings. In Alaska they eat moose calves and salmon. In the Adriondack park in New York State, they eat a lot of deer calves.

The bear's diet changes with the season, as does the availability if their food. In the spring, they eat mostly carrion, vegetation, and hunt small game, because they need to replenish the fat lost over the winter. In the summer, they eat a lot of berries, along with rodents and some small game. In the autumn they eat late ripening berries, fruits and nuts. During late autumn, early winter, they try to put on as much weight as possible, because the availability of food during wintertime decreases.

Reproduction and Life Cycle

Sexual maturity is reached at 3-4 years of age. In areas where food is abundant, bears may mate at 2 years old, in areas where food is less abundant, they may wait until 5-7 years old before having their first litter. The females typically mate every 2 years, but sometimes mate only every 3-4 years. Mating season is in June, July and August. The pair stays together for only a few days during the breeding season, and during this time they copulate many times. Female bears are induced ovulators, meaning they have to be stimulated several times in order to ovulate, so this is why they must mate so often. Also, like other mammals in the order carnivora, the male bears have a special bony structure in their penis called a baculum. This structure serves to stimulate the female into ovulating, as well as prolonging copulation by widening to lock the two mating bears in a copulatory "tie". This tie may last for 10 - 30 minutes. The fertilized eggs are not implanted in the uterus until 5 months after conception. Pairs do not mate for life, and remain together only for a few hours or days during the mating season. The males do not help raise the young. A male bear may father more than one litter of cubs a year, and tries to mate with as many receptive females in his area that he can.

During her pregnancy, the female bear goes into dormancy in a den after building up her fat reserve for the winter. Pregnancy lasts 220 days, and they usually have a small litter of two or three cubs born in a den in January or February. The cubs weigh 8 - 11.5 oz (225 - 330 g) at birth, and are devoid of hair and cannot see or hear.

The black bear cubs increase in size by about 2.75 oz (77 g) per day. Bears, unlike any other mammal, are born very small, much smaller than mammals of a similar size. In fact, when they are born, their weight is 10% of that of a mammal of similar size. The reason bears are born so small is because their mother fasts (does not eat) during the gestation period (pregnancy) with her young, unlike any other mammal which continues to eat while pregnant with her young. The mother bear's body proteins actually break down to provide glucose in order to nourish the young while they are still inside her. And since the baby bears obtain very little nutrients while still inside the mother, they are born premature. To make up for the lack of nutrients during gestation, the milk of bears is more rich in nutrients than other carnivores. Because the milk is so rich in fats and nutrients, young bear cubs do not need to drink as much milk as other carnivore cubs. The cubs are usually weaned at 6-8 months, but may remain with their mother for a year and a half. They reach full size at 4 years old. The black bear is very long-lived, living for up to 32 years in the wild.

Social Behavior

Male and female black bears lead solitary lives, coming together only to mate. They tend to be active at different times of the day depending on where they live, and the seasons. During the spring, they are most active at dawn and dusk, in the summer they are most active during the daytime, and in the fall they are active equally throughout the day.

Bears communicate with each other using scent, sound, and sight. American black bears tend to be the most vocal of the bear species, due to the fact that they spend so much time in the forest. And like other carnivores they mark their territories by rubbing on objects such as trees, and urinating on raised objects. Urinating to mark territory, however, is rarely seen outside of mating season. Also, claw marks on trees help to enforce the scent left.

American black bears are adept tree climbers, due to their smaller size. This comes in handy for escaping from other animals like brown bears, man, and even a pack of wolves or coyotes.

They are very aggressive animals, and will fight other bears and animals to protect their territory. However, if a fight can be avoided, it is, since bears can do serious damage to each other. Using frightening visual signals, such as standing on their hind legs and baring their teeth, they scare away a potential threat. The majority of bear fights occur during the mating season, as males will compete with each other over the limited number of receptive females. Female bears are not receptive every year, in fact they may go for 2-3 years without mating to raise their cubs. Thus male bears will readily kill cubs, so that they have a chance to mate with the mother. To avoid such conflict, females are very secretive, and have smaller ranges than the males. They will also attack the males fiercely, because she puts so much time and effort into raising her cubs, if they are killed each time she will have no reproductive success. Even so, male bears account for up to 70% of young bear deaths.

American black bears are very territorial; they keep large home ranges. A typical territory for a female can range from 1 - 15 square miles (3 - 40 sq km), and for a male 8 - 40 sq mi (20 - 100 sq km). A male's territory is typically larger than the females', and often overlap several females' territories. Territorial boundaries never overlap with those of the same sex. Young females often establish territories within their mother's for a few years, while all males are dispersed from their mother's territory at one and a half years old. Territory size varies form year to year, depending on the availability of food and the population density.

Contrary to popular belief, bears do not actually hibernate, they just go into dormancy. Not all bears do this; males typically don't, and bears living in the tropics don't either. It is not considered hibernation because the bears' metabolic rate does not drop as much as in animals that do hibernate, and unlike true hibernators, they can awaken at any time during their dormancy.

Threats

Natural threats include a variety of diseases and parasites. The most common parasites are ticks, fleas, mites, lice, tapeworms, roundworms, hookworms and flukes. A disease that seems to affect bears the most is the roundworm: Trichinella. Although more common in brown and polar bears, it is still commonly found in black bears as well. The American black bear is not endangered. However, they are often shot as vermin or killed for sport.





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