| The Grizzly or Brown Bear |
 Brown bears can be thought
of as direct descendants of the main lineage of
the family Ursidae. Their ancestors have
evolved from the ancient Ursavus
“bear dogs” primarily in Asia. Over
time, this lineage gradually evolved to adapt to
the colder climates in the north. Among the
more important adaptations were the ability to
hibernate during periods of food shortage and the
ability to store large amounts of fat. Brown bears are generally considered to undergo four annual stages of biochemical and physiological change. 1) The dormant stage is termed winter sleep or hibernation and is discussed in greater detail in the chapter Form and Function. 2) A modified dormancy, termed walking hibernation, is a transitional stage between hibernation and normal activity. 3) During normal activity brown bears can not suddenly switch on the state of hibernation; if they are deprived of food they will begin to starve and utilize muscle tissue to survive. If deprived of water they will become dehydrated. During the normal state bears feed, sleep, defecate, urinate, and breed. 4) As the period of hibernation approaches, bears greatly increase their food intake in the stage called hyperphagia. The excess food is deposited as fat, or adipose tissue, and they gain weight. The layers of fat provide a source of energy during hibernation and insulate the bear from the cold. Fat is especially critical for the first few weeks after emergence from the den in spring when food is generally scarce, but the bear’s metabolic demands have increased. Scientifically, more is known about the brown bear than any of the other bear species except for the American black bear. The brown (or grizzly) bear and the other five species of the Ursid family of bears have evolved recently and share many similarities. In popular terms, the name brown bear generally refers to coastal and Eurasian populations, while grizzly bear refers to interior populations in North America; all of them have the scientific name Ursus arctos. There are wide variations in color and size which appear to be due primarily to environmental differences. Size is probably correlated closely with the amount of nutrition available in the diet; thus coastal bears with access to salmon, a richer variety of plant foods, and milder weather conditions with a longer time period for feeding, are about one-third again larger than bears in interior populations. Brown or Grizzly bears have adapted to diverse habitats; from the Arctic tundra to the edges of the Gobi Desert. Wherever they live though, they have the same requirements as other animals; adequate food, shelter, protection from predators, and the opportunity to find a mate and produce offspring. Although tigers, wolves, and mountain lions may have the ability to kill brown bears (especially cubs) their only real enemy is man. And men are such effective killers of bears that even though an area may have everything else that brown bears need, if it is easily accessible to people, brown bears will probably not use it. The exception to this is in areas where bears are totally protected such as National Parks. In these areas, where bears have not learned to immediately fear humans, they are able to coexist with man.\par }{\plain \tab Bears are very intelligent animals; the experience of zookeepers and animal trainers indicate that they are smarter than dogs. This intelligence has enabled them to live in extreme environmental conditions and to exploit and learn an encyclopaedic array of food species and local places. They spend several years with their mother learning from her what plants are good to eat and where to find them. They also learn by themselves from experimentation. Orphaned cubs have learned how to catch and eat salmon on their own. By the time that subadult bears leave their mothers and take off on their own they know what plant foods are available at each time of the season, and they know what habitats are likely to have those foods over a very large area. As they leave their mothers and move into new areas they learn and remember where food is available. This knowledge is critical. Food sources change drastically from year to year depending upon weather and climate. A grizzly bear is often required to remember a type of food and where it was found that it may have last encountered ten or more years earlier. The ecology of brown bears in four parts of the world is discussed in more detail:
Some valuable grizzly bear links include: The IGBST, The IGBC and the IGBC links page, The IBA and the IBA links page, and the exhibit Bears: Imagination and Reality. Look for more links here in the days and weeks to com.
Picture
courtesy of Harriet Corbett, Rox Graphics, 866
Rd. 7RP, Powell, WY 82435, 307 645 3202, crowhart@wtp.net |