Magazine article Natural History

Bear Facts and Figures - Bears: Majestic Creatures of the W

Magazine article Natural History

Bear Facts and Figures - Bears: Majestic Creatures of the W

Article excerpt

BEARS: MAJESTIC CREATURES OF THE WILD, edited by Ian Stirling. Rodale Press, $40.00; 240 pp., illus.

The interaction of bears and people, which goes back at least to Neanderthal times, has taken on fascinating new twists and turns in the last twenty years because of the research of field biologists. In selecting the wide-ranging essays for Bears: Majestic Creatures of the Wild, editor Ian Stirling has assembled much new information answering some old questions.

We have long known, for example, that tiny, newborn bears are less than 10 percent of the size they should be according to the usual weight ratios of mother to offspring in placental mammals. A newly posited explanation for this disproportionate tininess of ursine newborns is the physiological inability of a bear fetus to utilize the fatty acids available to it through the placenta. According to this theory, the fats must first be converted to glucose in milk, so the offspring must be born before it can take on significant weight.

According to a new scenario for the initial human occupation of North America, the huge short-faced bear, now extinct, may for centuries have blocked Asian migrants' way to the interior. As carnivorous as the polar bear, longer-legged, and therefore faster, this predator may have so threatened the earliest settlers that they initially migrated south along the Pacific Coast rather than east into the continent.

Perhaps the most striking characteristic of the world's northerly bears is their ability to stay in winter dens for as long as six months of the year. Since the bear does not eat or drink during hibernation, its life seems to swing between extremes of fasting and feasting. But what at first looks only like a fat bear going in and a thin bear coming out is far more complicated than it appears. The bear is not completely inert--the whole sequence of gestation and birth takes place in the den. But what are the potential deleterious effects of such immobility? Why don't the bear's bones lose calcium and become brittle? And why isn't the animal poisoned by the accumulation of its own uremic wastes from cellular breakdown? And why do bears suffer less general debilitation from obesity than humans? These metabolic phenomena are beginning to be studied and may have important implications for the medical treatment of aged or immobile humans, as well as for space travel.

Bears have been described as "solitary," but new studies document instances of social behavior, such as brown bears tolerating one another at salmon rivers and polar bear females denning in communities. Another remarkable aspect of bears' behavior is their ability to navigate over long distances. Brown bears, if displaced by humans, are capable of returning several hundred miles to their home range. But how do they construct their mental maps? The answer seems to have several parts. One is that they have extremely good memories. A young American black bear that had followed its mother twenty miles to a feeding area, for instance, was known to return to the same place for three to five years afterward. Even more unexpected is evidence that bears sense the earth's magnetic field and can locate themselves in its gradients.

Recent study of the American black bear has shown that much of its sense of place is defined by scent marking. What appeared in the past to be merely scratching is now understood as a communicative function in which bears, like many other large mammals, persistently signal their presence in their own home ranges.

Perhaps the most exciting new information has to do with the bears' adaptation to human presence. Like modern researchers among wild primates, students of the ursids are finding that bears, particularly black bears, which may initially threaten or flee from humans, can become so tolerant that people may move freely among them so long as they respect the female bear's concern for her young. This not only means that field studies can be undertaken at close range but also that bears and people can learn to live together without friction. …

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