Grizzly Bear - Natural History

Text by Liz McKenzie      Photos and Sounds by Richard Nelson


Meeting the Great Bear

An autumn evening in Denali National Park; the tundra hills cloaked in a brilliant mosaic of gold, amber, and purple; a dusting of fresh snow on the high peaks. From the nearest ridge comes a clatter of tumbling rocks…and the source becomes quickly, startlingly clear.

A grizzly bear—excavating the hillside like a long-clawed backhoe. Nose to the earth, the bear seems oblivious to everything except the freshening scent of his prey—an arctic ground squirrel deep inside a stony burrow. The grizzly's massive shoulder muscles ripple beneath his dense coat of light tan fur; his body heaves up and down; his stocky hind legs brace against the slope.

Then a tiny squirrel bursts out from the fracas with the enormous bear inches from its tail. The air is alive with sounds of thudding paws and huffing breaths…but within seconds everything falls silent. Suddenly still, the grizzly peers down into a burrow, as if he's deciding whether to give the lucky squirrel a reprieve or dig again. Then he turns, rumbles a short ways along the slope, rolls back on his enormous haunches, and stares off toward the distant northern sunset.


Coastal brown bear feeding on a tidal flat
Interior grizzly bear

Grizzlies and Browns: A Tale of Two Bears

There is simply nothing more impressive, more captivating, more emblematic of the North American wilds than the grizzly bear. But despite all the stories that are told about these animals, despite their largely undeserved reputation for fierceness, and despite their prominent place in the human psyche—very few of us know much about them.

Alaska is the last American stronghold for the grizzly bear and for its larger twin or alter ego, the brown bear. Let's start with a look at this often confusing pair.

Most people think of the brown-furred bear with the humped shoulder and "dished" or concave facial profile as a "grizzly bear". But in Alaska there is another way to look at these great animals—by their habitat. Alaska's estimated 31,000 grizzly bears live in several different habitats—arctic tundra, interior forest, and coast.

What a bear has to eat and the climate it lives in has a dramatic affect on what it looks like and its way of life. For this reason, bears in Alaska are often called either "brown bears", for those along the coast or "grizzly bears" for the interior and arctic bears.

You Are What You Eat

If you were a bear and you wanted a lavish lifestyle, you'd prefer to make your living along the coast of Alaska, especially in a place like Kodiak Island. Here in early spring, after emerging from their dens, "brown bears" soon find lots of grasses and sedges to break their long winter fast, and possibly carcasses of deer that didn't survive the winter.

That famous shoulder hump is the result of bone structure and strong muscles, which evolved for digging, rolling logs, and for short, powerful bursts of speed—up to 40 miles per hour to catch prey. The bears look for insects under logs and dig for plant roots. In places like the Katmai Peninsula brown bears have even learned to dig for clams and to crack them open for a nutritious snack from the sea.

In summer, coastal brown bears also gorge on a wide variety of fresh green plants and nutritious berries—salmonberries, huckleberries, blueberries, and currents. Above all, most of the bears move to salmon streams where from mid-summer into fall, they can pack on the pounds by dining on fatty, protein-rich fish.

These bears can eat about 80 pounds of food daily, gaining about 5 pounds of fat each day.

Bears eat so much that along streams it's not uncommon to find salmon that have been "high-graded" by bears—meaning only the rich belly meat and brains have been munched. Bears are experts at catching salmon, even ducking their head or diving completely under water to look for fish, or snatching salmon in midair as they leap up the waterfalls. Mother bears teach their cubs how to fish and some cubs actually show distinct fishing styles that their mothers taught them.

Listen to brown bears fishing and fighting.

Since the coastal climate is mild by Alaska standards, brown bears go into their dens later in the fall and emerge earlier in the spring, compared with arctic and interior bears. These well-fed bruins go to sleep fat and when they wake-up in the spring, they don't have long to wait for a lush green salad of grasses and sedges.

Interior and arctic "grizzlies" live a much leaner life than their coastal counterparts. Food is scarcer and the intensely cold winters are much longer. When arctic bears leave their dens in the spring, green-up hasn't started, so the food selection is a bit grim—mostly over-wintered berries and animal remains.

After green-up, there are grasses, sedges, tubers, roots, even furtive artic ground squirrels and other small rodents, and possibly a newborn moose or caribou calf. Bears who live along the artic coast may scavenge on the carcasses of walrus, bowhead whales, or other marine mammals that have washed ashore.

In late summer and fall, berries are a very important food source for interior and artic bears. Their selection includes cloudberries, cranberries, crowberries, raspberries, soapberries, and by far the most important—blueberries.

There are salmon runs that reach interior Alaska, but nothing on the scale of the true salmon feasts along the coast

While grizzly bears in interior and arctic Alaska generally find enough to eat, they have to work a lot harder for it.

A Story in Numbers

The statistics for browns and grizzlies also tell the story of their different life circumstances—one lean and one lush.

While interior and arctic grizzly bears are no slouches when it comes to size, their coastal counterparts are bigger. And the biggest of all are the Kodiak and Katmai Peninsula bears, which can tip the scales at up to 1500 pounds or more for the biggest males, in the fall when they're at their heaviest. Interior male grizzlies' top weight is 600-700 pounds.

The density of bears in an area is another measure of the abundance or scarcity of food. On Kodiak and Admiralty Islands and in the Katmai Region, there is roughly one brown bear per square mile. At the opposite extreme, in the far northern Brooks Range, there is only enough food to support a very small and widely scattered population of bears—one grizzly for every 30-45 square miles.

A bear living on Admiralty Island doesn't have to travel a long way to find food, and it shows in the average home range—for a female brown bear that's about 10 square miles. Compare this with the North Slope, where a female's range is about 130 square miles—she has to move almost constantly to find enough food.

Interior and northern grizzly bears live in country where the winters last much longer—females will enter their dens in about mid-September and emerge around late may. By contrast, in mild winters, some male Kodiak brown bears may not den at all.

Love and Family

No matter where they live, grizzly/ brown bears have other parts of their lifestyle in common—mating, hibernating, giving birth, and raising their cubs.

Bears mate in the spring. A male and female have about a week of romance—they'll stay together during this time, mating several times, and will sleep and eat together.

Females may spend most of their lives in company with cubs, while males are mostly solitary except when they're mating or with other bears along salmon streams.

Inside the pregnant female, her tiny embryo does not implant itself until fall. The mother spends the summer gaining weight in preparation for hibernation and growth of her fetus, and for nursing once the cub is born. This delayed implantation is a good strategy—in lean years, the embryo will not implant, and the fetus is aborted, so the mother can save her energy to keep herself alive through winter.

During the summer and early fall, the other bears are also busily scarfing up berries (their lips are especially well designed for combing berries off bushes), along with any other available food in preparation for winter.

Even cubs of the year, born about seven months earlier in the winter den, will have reached 60 or 70 pounds by fall.

Bears prepare their dens by excavating a cave like tunnel into the ground. In southeast Alaska some bears make dens down under the roots of old growth trees. A bear might also line its den with grass or other soft material.

Inside the den, bears enter a sleep-like state, rather than a deep hibernation like that of arctic ground squirrels that spend winter in a nearly frozen coma or suspended animation. The bear's body temperature lowers and its heart rate slows. It also won't eat, drink or eliminate waste while in the den.

Cubs are born into their dark, relatively warm den in January or February. A sow can give birth to as many as four cubs, but usually she'll have two. They are tiny, only weighing about a pound, hairless, and blind. But they quickly begin nursing on their mother's rich milk. By the time the little family leaves the den, the youngsters weigh about 15 pounds.

Mom, on the other hand, hasn't eaten for many months and has lost a substantial amount of weight. The males and females without cubs also fast during hibernation. Even though their metabolism has slowed, they have still been living off fat reserves, which is why some bears lose as much as 50% of their fall poundage.

Once they leave the protection of the den, first-year cub mortality is high—30 to 40%. Cubs may become undernourished, diseased, or die in accidents. Some cubs are killed by male bears and sometimes females will kill cubs from another bear's litter.

If all goes well during their first years, cubs usually stay with their moms until they emerge from the den in their third spring. They have learned skills essential for survival on their own. Even still, it is a dangerous time for young, inexperienced bears without the protection of their mom. Siblings will often stay together for a while, some even denning together the first post-mom winter.

Bears are very playful—cubs treat their moms like a jungle gym. They also frolic endlessly with each other and even older siblings will still play together.

Once they're off on their own, the range of daughters and their mother bear may overlap, but sons will go much further away to establish their territories.

Some female bears have lived to be thirty years old, while males typically do not live to be more than twenty, perhaps because of battles with other males during mating season, which can cause serious injuries and sometimes death.

A New Understanding

Ancient fossils found in China of Ursus arctos are dated to 500,000 years ago. Scientists believe this species may have been around for more than a million years. Brown bears were once widespread over much of Europe, Asia, Northern Africa and North America.

Grizzly bears most likely found their way into North America by crossing the Bering Land Bridge into Alaska from Asia between 50,000 and 100,000 years ago.

Before 1850, grizzly bears were abundant in Alaska, Canada, and the lower 48 states. It is estimated that 50,000 to 100,000 bears lived in what is now the United States. Then these bears were nearly hunted to extinction. Today, less than 1,000 bears live in isolated populations in Wyoming and Montana, with a few in Idaho and possibly Washington State. Another 15,000-20,000 grizzly/brown bears live in Canada.

The deliberate extermination of these big bears was primarily brought about by a deep fear and misunderstanding.

But today, people have a new appreciation for grizzly bears—and for what their presence in the country means.

Much more is understood now about how intelligent and adaptable these bears really are. Bears have a very strong sense of smell, acute hearing and excellent eyesight. In Alaska, they've adapted to life on open ground left after the glaciers receded and have further learned to live and thrive in coastal areas, rain forests and interior boreal forest and mountain country.

They've even provided the evolutionary source for bears adapted to life on the sea ice. DNA evidence shows that bears on Admiralty, Baranof, and Chichagof Islands (often called the ABC islands) in southeast Alaska, are more closely related to polar bears than they are to other brown and grizzly bears. This suggests that one branch of the grizzly family—from which both polar bears and the ABC bears descended—moved onto the ice to hunt for food and gradually evolved into the modern polar bear. In fact, even today grizzly bears have been seen out on the sea ice close to shore, and very rare hybrid grizzly-polar bears are known from arctic Canada.

Since frontier times, people treated grizzly bears as terrifying beasts that kill livestock and threaten human lives. Often the motto has been "The only good grizzly is a dead grizzly." But recently those old attitudes have changed, as we began to respect these great animals, better understand their behavior, and learn how to behave in ways that do not threaten the bears while also keeping ourselves safe.

In Alaska, special places like McNeil River and Katmai National Park, not far from Anchorage, and Pack Creek and Anan Creek in Southeast have given people unparalleled opportunities to get very close to bears and to safely observe their behavior. In situations like these, biologists have come to a far better understanding of how bears interact with and communicate with each other. And through these observations, we now know how humans should behave around bears to minimize the danger and maximize the rewards of keeping company with these amazing animals.

Tourists visiting Alaska—and residents too—often say that seeing a bear is one of their top lifetime experiences—quite a contrast to the fears and misunderstandings that nearly exterminated grizzly bears 150 years ago.

And it is also said that just knowing grizzly bears exist in a place means knowing that there is country wild enough so that one of the earth's most spectacular creatures can still have a home. If we protect these places, our children's children will have the chance to experience this wildness too.

"Those who have packed far up into grizzly country know that the presence of even one grizzly on the land elevates the mountains, deepens the canyons, chills the winds, brightens the stars, darkens the forest, and quickens the pulse of all who enter it."

--John Murray     

For listening:

Bear Safety
Bears and Wildness
Tongass Bears and Salmon

For further reading:

Alaska's Bears by Bill Sherwonit
Hunters of the Northern Forest by Richard Nelson
Make Prayers to the Raven by Richard Nelson
Salmon in the Trees by Amy Gulick

For viewing:

PBS Nature Bears of the Last Frontier: City of Bears
PBS Nature Bears of the Last Frontier: The Road North

Important links:

US Fish and Wildlife Service
Alaska Wildlife Notebook Series
Alaska Department of Fish and Game

 

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