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Today, the bear family, Ursidae, consists of 9 species. Until recently, giant pandas and red pandas were classified as members of the raccoon family, but DNA studies in the 1980s established that pandas were more closely related to bears. Some scientists believe that the giant panda and the red panda should be placed in their own family, the Ailuropodidae. Bears are found on all continents except Australia and Antarctica. Most bears are solitary and omnivorous which means that they feed on a variety of foods, including animal and plant matter. They tend to move slowly but are very capable of running fast if necessary. Some bear species undergo a period of deep sleep over the winter, when food is scarce. This phase is not true hibernation because the body temperature only drops a few degrees and the bear is capable of quick arousal. During this time they do not eat, drink, urinate or defecate. Before entering the den they must fatten themselves up (their body weight may double) and the fat is broken down as fuel. Pregnant females may give birth at this time, when the cubs are safe within the den. Most species of bear undergo a period of delayed implantation during reproduction; the fertilised egg floats around in the uterus for several months before attaching itself to the wall of the uterus and beginning development. This enables the female to give birth to her cubs at the most suitable time. If food availability is poor, the embryo is reabsorbed by the mother's body. Unlike other carnivores, which walk on the tips of their toes (digitigrade gait), bears walk on the soles of their feet (plantigrade gait) as humans do. Bears have an aggressive reputation, but in most cases this is undeserved. |
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