Why are grizzly bears more aggressive than our black bears?

Why are grizzly bears more aggressive than our black bears?


Richard H. Yahner is a professor of wildlife conservation. This essay was excerpted from his book Fascinating Mammals: Conservation and Ecology in the Mid-eastern States , published in 2001 by the University of Pittsburgh Press.

My Opinion

Grizzly (or brown) bears are magnificent, powerful animals that get their name from the "grizzled" hair. Grizzlies were respected and revered by Native Americans but were feared and hunted relentlessly by early European settlers venturing west of the Mississippi River. In North America, two subspecies are recognized: one occupying mainland North America and another on the islands off Alaska. Grizzly bears once roamed areas west of the Mississippi River but now live only from Alaska to the northern Rocky Mountains.

Fear of grizzlies stems from that, compared to the more docile black bear, attacks by grizzlies on humans are often fatal. Grizzly bear-human confrontations may range from a bear entering a campground to obtain food to those in which a bear approaches, charges or follows a person. In particular, getting between an adult female and her cubs is extremely dangerous.

Why is the grizzly so much more aggressive and dangerous than the black bear? To answer this, we need to go back in time. Both grizzly and black bears evolved in Asia from the Etruscan bear about 2 million years ago. Etruscan bears were small, forest-dwelling animals capable of climbing trees to escape danger. Both grizzly and black bears entered North America by crossing a land bridge connecting Asia with Alaska. When bears arrived in North America, black bears remained in forests and retained the tree-climbing ability of the Etruscan bear, but grizzlies adapted to more open areas left treeless by glaciers.

Black bears are better tree climbers compared to grizzlies because they weigh two to three times less than grizzlies. Short, curved front claws of black bears facilitate holding on to tree trunks, whereas long front claws and powerful shoulder and back muscles (hence, the hump on the back) of grizzly bears are specialized for digging up roots, small mammals and other food items. As a result, grizzlies can't climb trees once they reach sub-adult size. Therefore, a female black bear with young responds to danger, such as an attack by dogs, wolves or a grizzly bear, by climbing a tree. On the other hand, a female grizzly with young "stands her ground" and wards off attackers.

Greater aggressiveness in grizzly bears also may be related to reproductive potential. A female black bear might raise 12 to 13 young in her lifetime, while a female grizzly produces only six to eight young in a lifetime. Hence, black bear young are more "expendable" than grizzly bear young. Increased aggressiveness in a female grizzly bear probably better ensures survival of her young to reproductive age and thereby better protects the "investment" in each offspring.

When in grizzly bear country, humans can minimize encounters with grizzly bears in a few ways. When camping, food and garbage should be stored in bear-proof containers located at least 100 meters from sleeping areas. When hiking, people should go in groups, follow heavily used trails and wear loud bear-bells or make loud noises. Bells, unlike whistling or yelling, provide bears with unambiguous information that hikers are in the area, reducing the chances of bears being startled or threatened.

Humans can protect themselves from most bear attacks by using commercial products referred to as "red pepper sprays." When attacked by a bear, the spray should be dispersed toward the bear as a cloud rather than a narrow stream; also, the liquid should not be sprayed into the wind because it might blow back into the user's face.

When a grizzly bear directs a full-charge toward you, all possible means of defense should be used to fight, e.g., pepper spray, rocks, sticks, firearms, clapping hands and shouting. If possible, climb a tree. However, if the bear is extremely close and the attack is imminent, you have two options. First, hope the bear just ate a deer or elk and is not hungry. Second, and seriously, use passive resistance, i.e., "play dead" and cover your head and neck area.

After graduating from Penn State, treat yourself to a visit to Denali National Park, Alaska, where grizzlies can readily be seen foraging in meadows for food. However, don't go hiking when a grizzly is known to be in the area, especially on the grizzlies' favorite day of the week -- Chewsday.