Ursus

There are five species of the Ursus, commonly known as the brown bears, black bears, and polar bears. These bears, yet in the same group, actually have a lot of differences. They differ in their appearal, habitats, and ways of reproducing.

Anatomy
The bear has a unique anatomy. Some characteristics of them contain five claws on each paw that do not retract, a short stubby tail, great senses of smell and hearing, and long shaggy fur. Colors of the fur come in varieties. Common colors are black, white, blonde/cream, and brown. Bears are very strong, and powerful. Most have large bodies and they are able to stand on the back two legs. Their snouts are long, and they have smaller, rounded ears. The paws are broad, and their teeth are used for eating (depending on what the bear eats), and for fighting and defending themselves. Depending on what species of the bear, they can have 32 to 42 teeth. The five claws that they have on each paw are very strong and sharp. They are used for many different reasons. Like climbing trees, catch prey, dig up roots, or even rip open termite nests or beehives. The male are almost always bigger than the females. But the difference between sexes varies and is greatest in the largest species. A bear's life span seems to last about 25 to 40 years. Bears living in the wild tend to die younger than their zoo-counterparts. For how big the bears get, this results in a high weight. They range in weight from eighty to more than 600 kg. Ursus arctos is the largest down the coast of southern Alaska on nearby islands. There, the bears can weigh as much as 780 kg. But to the north and east, the size of them decreases.

Reproduction
The reproduction of bears is also unique. Bears reproduce seasonally, usually after a period of inactivity similar to hibernation. They reproduce sexually. When a baby bear or cub is born it has no teeth, hair, or eye sight. Cubs are usually born in a litter of one, two, or three. And they usually stay with their mother for the first six months of their lives. After three months, they will start hunting with the mother, yet at first they are fed by milk. They soon detach from their mother, but they stay close for about three years or so. At seven years, the cubs reach their sexual maturity. Some female bears copulate with a lot of males during estrus. Estrus lasts about 10 to 30 days. The males fight over the females and guard/protect them for 1 to 3 weeks. The fertilized eggs develop to the blastocyt stage, after which implantation in the uterus is delayed. About five months after mating, the blastocyt becomes implanted. This usually happens when the female starts her hibernation. Following, is a six to eight week gestation. Total gestation time, including pre-implantation, ranges from 180 to 266 days.

Ecology
Bears live in many different kinds of habitats. They live from the tropics to the Artic. Some live in desert edges, high mountain forests, and ice fields. Their home ranges can be as big as 2600 sq km, although on an average its between 73 and 414 sq km. Male’s range about seven times greater then the female.

Most bears are omnivorous, but some are exclusively carnivorous, like the polar bears. Some bears are also known to hibernate during the winter season to preserve energy.

Related References

 * Ursus wikipedia
 * Ursus ursusinternational
 * Ursusanimaldiversity