One of the main reasons Kodiak bears grow so much larger than inland grizzly bears is due to the abundance of food on Kodiak. Not only can bears feast on protein-rich salmon in the summer, but the archipelago is loaded with nutritious vegetation and sugar-packed berries. A brown bear’s jaws have powerful muscles and teeth that have evolved to adapt to an omnivorous diet of both plants and animals. Kodiak bears are opportunistic feeders. They eat roots, berries, grasses, sedges, wildflowers, wild celery, and other plants, as well as rodents, insects, large mammals (including deer and mountain goats), fish, carrion, and yes, unfortunately, garbage and pet food.
Bears’ stomachs contract during hibernation, and when they first leave their dens, they aren’t hungry. They eat little at first, concentrating on emerging plants and their roots. As the spring progresses, Kodiak bears can be seen feeding in grassy meadows and look much like grazing cattle. Their diet switches to salmon in the summer months, when they chase and catch fish in shallow streams or on the tidal flats near the heads of the deep, narrow bays on Kodiak. Bears also consume dead salmon that have washed up on shore. When the salmonberries, elderberries, crowberries, blueberries and other berries begin to ripen on Kodiak in late July and August, most bears spend at least part of their day in berry thickets, pulling the berries from the bushes with their lips and mouths. Salmon provide bears with fat and protein, and berries are high in natural sugars, all of which are important for building up a fat reserve for hibernation. As fall progresses, bears increase their consumption of salmon and berries as they strive to build up their fat layer before entering the den for hibernation. A diet rich in berries has its downside, though. Bears are one of the few wild animals susceptible to tooth decay. Abscessed teeth are not uncommon, and rotten teeth may affect the bear’s ability to eat and may even lead to starvation.
One of the most enjoyable aspects of bear viewing is watching a bear chase and catch a salmon. Sows teach their cubs how to fish and will often corral a salmon toward the cub in shallow water and then encourage the cub to chase the fish. A sow with newborn cubs that are still nursing will only allow her cubs to eat a small part of her catch after she has had her fill because she needs the extra protein to produce the milk to nurse her cubs, and the cubs are receiving most of their nutrition from her. As the cubs age, they nurse less, and the sow shares more of her catch with them. Finally, when they are old enough, she encourages them to fish on their own, and by the time the cubs are two years old, they can usually chase and catch a few salmon without the help of their mother.
Fishing is a skill bears learn with much practice over time, so young bears are often clumsy fishermen. A sub-adult bear may gallop back and forth in a stream for thirty minutes without successfully landing a salmon, while an older bear walks slowly downstream and pounces on a passing salmon with little effort. A bear may also develop his own unique fishing technique. One bear may sit on a fallen log hanging low over a stream and attempt to grab fish as they swim past. A second bear may “submarine” by dunking his head under water to watch for fish, and a third may obtain his fish by chasing another bear and stealing that bear’s catch.
A Kodiak bear’s coat may range from dark brown to nearly blonde. Bears are typically darker in the fall when they begin growing their winter coat, and older bears are often darker than younger bears, but these are just generalizations. One cub from a litter may be light, while his brother is dark brown.
Cubs often have a natal collar, a white band around the neck and shoulder. Some cubs have no natal collar, and others have a collar that is bright and distinct. This band gradually fades over time, and it has usually disappeared by the age of three, but occasionally, you will see a four-or-five-year-old bear that still has remnants of a collar.
A bear’s fur is an excellent insulator. It is dense and oily, keeping the bear warm and preventing water from penetrating. The fur consists of two types of hair, the “guard hair” and the “under-fur.” Bears shed both the guard hair and underfur annually. In the summer, Kodiak bears often appear shaggy and matted. The bear in the photo below looks as if she is sporting dreadlocks. To help remove their fur, bears rub against trees and rocks, often standing on their hind legs, backing up to a tree and rubbing up and down. It is humorous to watch a bear “scratch his back” in this manner. While the old coat is shedding, a new coat is growing, and by September on Kodiak, most bears appear darker in color and well-groomed. The old, loose fur is gone, and only the new fur remains.
Brown bears have non-retractable claws up to four-inches long. The claws of young bears are typically dark brown and then lighten with age. Although some young bears have light-colored claws, beautiful, pearly-white claws are usually seen on an old sow or boar. Look at the photos and notice the difference in claw coloration between the sub-adult bear and the old sow.
Brown bears use their claws to defend themselves and fight with other bears, but Kodiak bears primarily use their claws to dig for roots and other food and gripping food. Even though their claws look large and clumsy to us, they are quite dexterous and capable of manipulating small objects. Kodiak cubs use their claws to climb trees, but adult brown bears are poor climbers due to their body weight and the structure of their claws. It is not uncommon to see a sow send her small cubs up a tree if she senses danger, and they stay in the tree until she vocalizes the signal that it is safe for them to come down.
Bears, like all animals, depend on their senses to survive. They use their senses for many things, but especially to find food and detect possible threats. A bear’s sense of smell is its most important sense. A brown bear’s sense of smell is three to four times more sensitive than that of an average dog, and it is difficult for humans with our relatively poor sense of smell to comprehend what this means and how much a bear depends on this sense. A bear uses his nose to find food, locate a mate, and avoid danger. A bear downwind from you may smell your presence and run from you while you are still several hundred yards away from him.
A bear’s second most important sense is hearing. Brown bears have relatively small ears, but they can detect noises at a great distance. A bear can hear the click of a camera shutter over the sound of the wind, crashing waves, or a swiftly running river.
For a long time, biologists believed bears had poor eyesight, but scientific research has shown a bear’s eyesight is similar to that of a human’s. Bears are not nearsighted as was once believed, and they can see colors. Brown bears often stand on their hind legs to increase their sight distance and get a better look at an object. It is not a sign of aggression when a bear stands on its hind legs; the bear is just trying to gain more sensory input.
The important thing to remember is a bear does not use each one of these senses independent of the others. If a bear sees something unfamiliar in the distance, such as a person, a boat, or even another bear, he may stand on his hind legs to get a better look, raise his nose to attempt to smell the interloper, and pick up his ears to try to ascertain unfamiliar sounds. If he still cannot determine what the object is, he may approach it for a closer look or circle downwind from the object so that he can smell it better.
Next week, I’ll write about a bear’s fur and claws. Does a bear’s fur change with age? Why are some Kodiak bears blonde and others a chocolate-colored? What is the white ring some cubs have around their neck? How do the claws change with age?
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Summer Friends at Amook Pass is a post by my friend, Marcia Messier. I love this humorous story about her animal encounters while she worked for us at Munsey’s Bear Camp. What Marcia doesn’t tell you in this piece is that I named our goat visitor Marcie because the goat’s daring trip each summer from the mountains to the ocean, reminded me of Marcia’s adventurous spirit. Prepare to smile as you read about Marcia’s adventures!
During the summer months at Amook Pass, the animals were my friends. That sounds a bit corny, but they were amusing, startling, and comforting, all that friends should be. I looked forward and anticipated who might stop by for a visit during my busy days.
I was privileged to know Gizzy, Fletcher, Elsie, and Olive during my summers at Munsey’s Bear Camp. They were my very best animal friends. I thought it was interesting that Gizzy and Olive had similar personalities as did Fletcher and Elsie; even though, they had never met. Gizzy and Olive were the sweet ladies, soft-spoken, polite, accommodating for a photo, well groomed, and perhaps just a little bit shy of visitors. Fletcher and Elsie, on the other hand, were true wilderness cats. Fletcher was getting along in years when I first met him, but he told me many a hair-raising tale about his hunting skills as a younger gentleman. Elsie was in her prime, and she loved to stalk bears for days on end. Many a time as Robin and I were mourning her early demise, we would hear Mike yell, “Elsie’s back!”, and there she would be, dragging herself through the door, ragged, dirty and ravenously hungry after her latest adventure.
Fletcher and Elsie loved to hunt voles, the tiny mouse-like creatures close to the bottom of the Kodiak food chain. They must be a very tasty snack because twice daily I’d find their tiny blue and green left-over parts deposited on the front door step. I used to tell myself they were loving gifts, but then again, whoever left the pieces always seemed slightly amused when I reached down to pluck the bits off the doorstep while making slight gagging sounds.
Freddie the Weasel became a daily late-afternoon house guest. Maybe the sound of the old generator starting up interrupted his afternoon nap. He’d shoot in the backdoor, zip through the kitchen and take cover under the couch in the living room to watch and learn about life in the big house. At first, I jumped and shrieked thinking he must be some kind of Kodiak rat, but later in the day, Robin calmly explained about weasels.
Gizzy and Fletcher were still with us then but getting along in years. They knew their limitations, so they decided to pretend Freddie was just a figment of my over-active imagination. Not wanting to insult them, I went along with the game and soon we all looked forward to Freddie’s daily antics. I knew when he heard the boat motoring up to the mooring; I would see the tail end of Freddie flip out the front door.
Early in the summer season, the female Sitka deer would bring their fawns into the yard to nibble the bright green salad-like greens growing around the cabins. Sometimes there would be twins, and I would think happy thoughts as I watched them through the kitchen window while preparing breakfast.
One day I came nose to nose with a deer! I was hurrying to the cabin with a load of fresh laundry, and we met coming around the corner at the same instant. We were both startled and just stared dumbfounded into each other’s eyes for a moment. I’m not sure who moved first, but a hunter later told me I was lucky it hadn’t given me a good kick in the shins before it bolted off! I guess that happens, but ours was a peaceful meeting, and I will forever remember that instant.
I live in Arizona, so the first time I saw a fox on the pathway, I excitedly reported to Mike I had seen a coyote in the yard that day. Laughing, he looked at me like I was nuts and said, “There are no coyotes on Kodiak Island!”. I felt a little foolish but still maintain at a distance, a big healthy Kodiak fox looks very much like a thin Arizona coyote in the summertime!
I’ve seen Bald Eagles before, but in Arizona, they are a special sighting. On Kodiak, they are commonplace, and I was thrilled to see a nesting pair close to camp. On my mid-day break, if the weather was good, I’d sit in a lawn chair facing the bay and watch the eagles fish. It was entertaining; an eagle would fly over the water and scope out a fish, and then in an amazing feet-first dive, catch the fish in its talons. After this, it was usually impossible to get airborne once again, so it had to row itself and the fish, still clutched in its talons, ashore with its wings. There, after expending so much energy, it would devour the fish and do it all over again.
More than once, on a nice day, while taking a siesta in the hammock, enjoying the warm sun on my face, I’d hear and feel the strong wing beats of a very large bird flying close over me, and I’d know I had been checked out by a Bald Eagle!
Some of you may have read my “Encounter” with a bear. I was walking along the path up to the guest cottage one afternoon, my mind far away, when I heard a “horse” snort. The sound brought me back to the present in a flash, and I must say, I have never confused the sound of a bear with that of a horse again!
A secret I’d like to reveal is Mike used to make a bear playground out of old red mooring buoys a distance up behind the generator shed. I heard him and Robin laughing once about how much fun the bears had rolling, tossing and chewing these old red buoys. I never did venture up past the generator shed and burn barrel. Wearing a red jacket, I didn’t want the bears to make a mistake. I did wonder if mother bears warned their cubs, “never go near that playground as there is a dangerous human there who makes frightening loud, smoky blasts come out of the shed and soon after makes fire leap high into the sky out of a barrel!” Thinking back, I was probably quite safe.
Marcie was my favorite yard animal. One warm July day, we spotted a solitary mountain goat strolling along the beach near camp. Mike and Robin reported this was indeed a rare sighting. We couldn’t help ourselves, Robin christened her Marcie, and we began to speculate about her life and why she was here on our beach. She was a rebel. Marcie was tired of billies, she had too many youngsters to raise, and the constant stress of all those steep icy mountain ledges was wearing her down. Maybe she had arthritis in her knees. Maybe she just wanted a vacation at the beach! We happily welcomed her, and for a number of years, she would appear for her annual July vacation at Munsey’s Bear Camp. One year she didn’t arrive. We looked and looked, but no Marcie. Right away we decided, instead of feeling sad, we would celebrate her life. We had a toast to Marcie, how brave she was to break away from the herd and dare to be different!
The sea otter is a zen-like sight floating on its back, paws pressed together as if in meditation pose. It’s a sweet maternal picture with mom floating on her back and a tiny baby resting on her belly. And how clever of them to use tools! They often are observed with a rock balanced on their belly, happily cracking open clams for lunch. Brilliant!
At Munsey’s Bear Camp, I often saw sea otters floating in the cove in front of the lodge, and the sea otters kept to themselves. Their cousins the river otters, however, were a different matter. A family of river otters took up residence under the dock. This dock was now their home, and no one else was welcome. The dock became their dining room and their toilet. A mop had to be stationed on the dock so that the horrid stinky mess could be swabbed away. The mop could also be used as a defensive tool.
With guests arriving and departing from the dock every five days, caution had to be observed. One day stands out in my mind. It was a beautiful, sunny Kodiak day, and we were all on deck welcoming new guests. As they were embarking from the float plane and luggage was being handed down, I took a step back and slid on an unseen mound of otter poo. I wanted to vaporize as I fell on my backside in an ungraceful plop! Afterward, we laughed about this incident, but I never forgot, and every time I saw a sweet little otter posing for pictures, I saw two little horns poking up through the top of its head.
I grew up near Cape Cod where everyone loved to fish. I didn’t. To me, the whole process from baiting the hook, to dragging the poor thing out of its natural habitat with a hook in its mouth, to butchering it, to stinking up the house with fried fish was cruel and disgusting. Fast forward 40 years and I’m a cook in a fishing camp. I politely listened and smiled at all the fish stories and quietly cooked the fish, wondering what all the commotion was about. One day my perception changed. Robin and Mike asked me if I’d like to go out on the boat with them for the day. We had only one guest, and it was a great day to get out of the house. Yes, I wanted to go! Like a good sport, I purchased my fishing license, and away we went. Mike anchored in a pretty cove, and as I sat down in the deck chair ready to enjoy the sunshine, Robin stuck a baited pole in my hands and showed me where to drop the line. Still not paying much attention, suddenly the pole was nearly yanked out of my hands, and the line was whizzing off the reel. “What’s going on?”, I hollered. Robin and Mike replied, “You’ve caught a fish.” They proceeded to give me instructions. Suddenly, the scenario was hilarious, like an old re-run of “I Love Lucy.” I couldn’t stop laughing which in turn made my arms weak and unable to reel in the line. In a second, Robin strapped a belt-like thing around me to support the fishing pole so that I could reel. Now we are all laughing hard, but with perseverance and aching arms, the fish finally emerged from the deep. I was leaned over the rail gasping in amazement at “my halibut” when all of sudden, Mike, with an expert jerk of his pliers, freed my fish from the hook and off it swam! Hey! At that moment I was totally conflicted. On the one hand, I proudly wanted to bring my halibut home for supper, but on the other, I wished it well and was happy it was able to live another day in Uyak Bay.
How can any mammal be endemic to an island in the North Pacific? That mammal did not evolve on that island, so it had to arrive on the island at some point. I guess the answer depends on your definition of endemic. Most biologists believe that if a species was present on an island when the island became separated from nearby land masses, and if that species continued to survive on the island, then the species is endemic or native to the island. In other words, the species was not transported to that island by man. Experts list six mammals they consider endemic to Kodiak Island. These are the Kodiak Bear, the red fox, the river otter, the short-tailed weasel, the tundra vole, and the little brown bat. Over the next few weeks, I will discuss each of these mammals. I have already written several posts on Kodiak Bears, so I will mention them briefly here, and then in subsequent posts, I will focus my attention on the other five mammals.
At the end of the Pleistocene epoch, 12,000 years ago, ice sheets covered the North Pacific, connecting Kodiak Island to the mainland. At this time, bears and other mammals could roam freely between the mainland and Kodiak, and we assume that this was when the six mammals we consider native to Kodiak Island arrived on the island. When the ice receded and water levels rose, these mammals were trapped on Kodiak Island, where they adapted, evolved, and thrived. Humans would not arrive for another 4500 years.
After the ice receded, vegetation was scarce, but conditions slowly improved. Vegetation grew and became the jungle-like growth we know on the island today, and salmon runs became established in the many rivers and streams here. More than 3500 bears presently inhabit the Kodiak Island Archipelago, the largest number to have ever lived here. The bears thrive on prolific berry crops and rich salmon runs. Many mammals have been introduced to Kodiak over the years, and while some have negatively impacted the vegetation here, none seem to have affected brown bear abundance and vigor.
Kodiak brown bears exist only on the islands of the Kodiak Archipelago. The archipelago is located in the western Gulf of Alaska, approximately 250 miles (408 km) southwest of Anchorage. The island group is 177 miles (283.2 km) long and 67 miles (107.2 km) wide at its widest point. Kodiak, the most prominent island in the group, has a land mass of 3,588 square miles (8,975 km²) and is the second largest island in the United States.
In 2005, the brown bear density on Kodiak Island was estimated at 0.7 bears/square mile (271.2 bears/1000 km²), making it one of the densest brown bear populations in the world. This density estimate is a bit misleading, however, since bears are not evenly distributed across the archipelago. In the spring, summer, and fall, the bear density is much greater along the coast and salmon streams, while there are fewer bears in alpine regions. During the past decade, the Kodiak bear population has been slowly increasing. Recent genetic research has shown that while Kodiak brown bears are closely related to Alaska Peninsula brown bears and brown bears in Kamchatka, Russia, Kodiak bears have been isolated since ice sheets receded at the end of the Pleistocene epoch 10,000 to 12,000 years ago.
Over the next few weeks, I’ll write posts about red foxes, river otters, short-tailed weasels, tundra voles, and little brown bats.
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This past Memorial Day, my cousin and his wife, Mike and Mary Kohr, drove from their home in Minnesota to Marshfield, Wisconsin to visit Munsey and Boda at the Wildwood Zoo. Those of you have been following my blog know that Munsey and Boda are two of the three bear cubs we helped rescue last spring after their mother was shot by a hunter. If you haven’t read these posts, follow these links to read the first one and the second one.
We were thrilled that Mike and Mary planned a trip to see the bears. We had seen recent photos of the cubs and knew they were thriving, but from the photos, we only caught glimpses of the bear enclosure at the zoo. Mike promised to take photos and videos of the enclosure and to send them to us. The thumb drive with the photos and videos arrived a few days ago, along with a special treat: The Marshfield, Wisconsin Visitor’s Guide. Guess whose photos are splashed across the cover of the visitor’s guide? That’s right! Two spunky, healthy Kodiak Bear cubs dominate the visitor’s guide. Not only are their photos on the cover, but the guide has a nice, long article about the cubs and how they came to call the Wildwood Zoo home.
Mike and Mary’s photos and videos provided us with great views of the bear enclosure. This enclosure was completed just before the bears were transferred to the zoo, and it is spacious and beautiful. The Wildwood Zoo is not a large zoo, and the bear enclosure is the centerpiece of the facility. The enclosure cost 1.3 million dollars to build. Designers took an existing 1,200 square-foot outdoor exhibit and expanded it by adding 4,600 square feet. This enclosure includes a one-acre wooded area called the “Bear Woods,” and an enclosed bridge that spans 65 feet connects the woods to the primary exhibit area. Additional pools with recirculating water were added to the exhibit, and state-of-the-art containment and care facilities were added to the existing den building. The bridge joining the woods and the primary exhibit area is usually left open, allowing the bears to wander back and forth, but the bridge can be closed if the staff needs to isolate the bears from each other for some reason.
Here is what Mike Kohr had to say about Marshfield and the Wildwood Zoo: “Marshfield, Wisconsin is a small rural town of about 20,000 people. The Wildwood Park and Zoo complex is small but well maintained and seems to be very popular. The zoo itself is small and does not charge admission. It has mostly birds and a few mammals. However, the Kodiak Bear complex/exhibit is spectacular by any standard. I love zoos and have been to many around the world. Munsey and Boda are in a great place that rivals any bear exhibit I have seen.”
Mike said that wherever he and Mary went in Marshfield, people asked them if they had seen the bears. Munsey and Boda truly are the stars of not only the zoo but the entire town. For two little bears that nearly died from dehydration and hunger on a Kodiak mountainside, life at the Wildwood Zoo is very sweet.
Thank you, Mike and Mary for visiting the zoo and sharing your photos, videos, and observations with us. The Marshfield Visitor’s Guide is a treat that we will share with our guests. If any of you are in Wisconsin in the near future, take a little extra time and swing by the Wildwood Zoo to say hi to Munsey and Boda. E-mail your photos to me at email@example.com, and I will share them on my blog!
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To understand how strong a Kodiak bear is, you only need to observe one effortlessly running up a steep slope, quickly digging a den out of the side of a mountain, or easily flipping huge boulders weighing several hundred pounds. Kodiak bears have a heavy skeleton and a thick layer of muscles. The hump on their backs is a mass of muscles that aids in their ability to dig and provides a powerful striking force with their forepaws.
Brown bears have a shuffling, lumbering walk. They are flat-footed and pigeon-toed, and they walk with both legs on one side moving together. Their paws strike the ground in the following sequence: Right forepaw then left hind paw then left forepaw followed by the right hind paw. When walking at a fast pace, the hind paw is often placed well in front of the forepaw track.
Brown bears can run very fast over a short distance and have been clocked at 35 to 40 mph (56 to 64 kph). Even over a long distance, they can quickly cover a great deal of ground and climb steep banks with ease.
Many of our guests are surprised to learn that Kodiak bears can swim, but brown bears are excellent swimmers and can swim for a mile or two to cross a bay or lake. A brown bear swims with his body below the water and his head and nose slightly above the waterline. Although bears are strong swimmers, they seem ill-at-ease and vulnerable when swimming, and when approached by a boat, a bear may give up his plan to swim across the bay and return to the shore he just left, even if he is closer to the opposite shore. On sunny summer days, it is common to see Kodiak bears lying in water or splashing in the ocean to cool themselves, and some bears while even dive underwater to catch salmon. Snorkeling is a funny fishing technique employed by a few bears where the bear walks through chest-deep water and submerges his head to look for fish.
I never grow tired of watching bears. Sometimes they amuse me when I watch the interactions between a sow and her cubs, and other times I get caught up in the drama when two bears square off against each other. I am always amazed, though, by their tremendous strength and their ability to cover a great deal of distance in the blink of an eye. The combination of these two characteristics makes them the rulers of their domain.
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You don’t have to spend much time watching Kodiak bears to realize how intelligent they are. Some researchers consider bears to be as intelligent as primates, and others believe a bear is as smart as a dog. Intelligence is difficult to measure, though, and to compare the intelligence of bears to that of other animals is a guessing game. It is clear that bears learn quickly and remember what they learn, and unfortunately, this can be to the bear’s detriment if he learns to associate food with humans. Bears can adapt to environmental changes or unique situations, and they will remember what they learned from a single situation or experience.
Bears are only able to make a limited range of sounds, and they do not have the necessary muscles for facial expressions. They can’t curl a lip like dogs do, and their small ears don’t allow the expressive maneuvers of cats, but bears do communicate with each other by posturing, attitude, and vocalization. A sow may send her cubs up a tree with a woofing sound or call them to her side by popping her jaws. Many bear vocalizations sound alike to a human’s ears, but bears can differentiate the sounds and understand what they mean.
We often hear bears growl while fishing near each other, and sows frequently growl at their cubs to reprimand them. A loud roar is a much more serious vocalization than a growl, and a grunt or a woofing noise often signifies a distressed or upset bear. A bear will grunt or woof at us if he is surprised by our presence, and this vocalization sometimes precedes a lunge or a false charge. The message delivered by a vocalization has as much to do with the message giver as it does with the vocalization. A large boar needs only to stomp his feet or issue a sharp “woof,” and smaller bears flee his presence. Those same actions and vocalizations delivered by a sub-adult bear likely would go unnoticed.
Bears communicate with humans just as they do with other bears, and understanding their language or choosing a guide who understands their language is important if you plan to spend time in the wilderness in bear country. Correctly interpreting vocal signals as well as body language and posturing may alert you to back away from a stressed or agitated bear.
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Last week I posted about the mechanics of bear hibernation, but how does a large mammal manage to curl up in a ball in a cave and sleep for five months? Humans and other mammals would die if they tried to hibernate. During hibernation, bears do not eat, urinate or defecate. What physiological adaptations allow them to do this?
While in hibernation, a brown bear’s breathing drops from 6 to 10 breaths per minute to one breath every 45 seconds. His heart rate drops from forty to fifty beats per minute to nineteen beats per minute, but his body temperature decreases only a few degrees and does not drop below 88° F (31°C), which is within 12°F (6°C) of his normal body temperature. Some scientists consider bears to be “super hibernators.” Because they have thick fur and also a lower surface area to mass ratio than do smaller hibernators such as rodents, bears lose body heat slowly, which allows them to cut their metabolic rate by 50-60%. Physiologist Øivind Tøien at the University of Alaska Fairbanks has discovered that while a black bear’s body temperature only drops an average of 9.9° F (5.5° C), the bear’s metabolism plunges to 25% of the average summer rate. Furthermore, his studies indicate that when a black bear comes out of hibernation in the spring, it takes several weeks for the bear’s metabolism to return to normal.
The amazing physiological adaptations of bears during hibernation are of much interest to human medical researchers. If a human must endure prolonged bed rest due to paralysis or illness, if a broken limb is immobilized, or if an astronaut spends several months in space; the human body faces such risks as blood clots, heart failure, significant loss of muscle mass, a breakdown of carbohydrates, proteins, and fats, as well as life-threatening bedsores. A hibernating bear has none of these risks, including no loss of muscle function. Scientists are interested in determining what specific changes in metabolites, proteins, and hormones allow bears these physiological adaptations during several months of inactivity. Humans, as well as all other mammals who maintain non-weight-bearing positions for an extended period, suffer from osteoporosis, but bears do not lose bone mass during hibernation. When the secret to how bears accomplish this feat is discovered, it may help people with weak bones, patients who become bedridden for a prolonged period, people who suffer paralysis, and astronauts on long space missions.
While bears are hibernating and metabolizing body fat, their cholesterol levels are twice as high as respective cholesterol levels in humans. Bears, however, do not suffer from arteriosclerosis or gallstones, conditions which plague humans with high cholesterol. Furthermore, a bear’s liver secretes a substance that dissolves gallstones in humans. Insight into how bears recycle urea during hibernation could lead to advances in treatments for kidney failure and dialysis in humans. Also, bears gain a great deal of weight in the fall before going into hibernation, but unlike many obese humans, they remain insulin-sensitive. Conversely, they become insulin-resistant once they are in hibernation, so their fat does not break down too quickly, but when they wake in the spring, they once again respond to insulin. In other words, bears can put themselves into a diabetic state while in hibernation and then reverse out of it in the spring. Understanding what allows bears to do this could lead to breakthrough medical advances in the treatment of diabetes and obesity in humans.
There’s so much more going on with hibernation than simply curling up for a long winter’s nap. I look forward to reading new scientific studies on bear hibernation.
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Hibernation is one of the most amazing physiological adaptations in nature, and the more I learn about bear hibernation, the more the process fascinates me. Most bears have recently left their dens here on Kodiak, and they are slowly restarting their digestive systems as they prepare for the summer feeding season. Over the next two weeks, I’ll post about denning and hibernation for Kodiak bears. I wrote a post a year ago about den emergence on Kodiak, but this time, I will discuss hibernation in more detail.
Bears hibernate in the winter to conserve energy when weather conditions are harsh, and food is scarce. While hibernating bears experience a degree of dormancy, it is nowhere near as extreme as it is in many other species such as bats, squirrels, and rodents. On Kodiak where winters are relatively mild, bears often go into and out of hibernation and some bears (mostly boars) do not hibernate at all. It is common to see bear tracks in the snow all winter on Kodiak.
Bears typically enter their dens in the order of pregnant females followed by lone females and then females with cubs. Males are the last to enter their dens, and large, old boars in particular may not hibernate at all. Denning conditions vary from year to year depending on the weather conditions and the availability of food.
The time of den emergence in the spring is also dependent upon temperature and weather conditions and varies by sex and age. Males typically leave their dens first, followed by single females and then sows with cubs. Sows with newborn cubs are the last to emerge Males usually spend three to five months in hibernation while pregnant females may hibernate as long as seven months.
While there is an instinctual aspect to denning, it also appears to be a learned behavior that sows teach their cubs. Perhaps the most important information the mother bear relays to her cubs is how to choose a den site. On Kodiak, there are few natural rock caves, so bears must dig their dens into the sides of the mountains or the sides of snow banks. Lawrence Van Daele, Victor Barnes Jr., and Roger Smith studied and compared denning behaviors on the northern part of the island to those on southwestern Kodiak. On the northern portion of Kodiak where the mountains are taller, they determined that the bears in their study group denned at an average elevation of 2180 ft. (665m). The bears in this region preferred steep slopes in alpine habitat for their dens, probably because the dens were high enough that the soil remained frozen throughout the winter, and the den structure remained stable. On southwestern Kodiak Island with its gentler topography, bears denned at an average elevation of 1499 ft. (457 m) and preferred midslope habitats near alder thickets. The researchers believe that the alder roots help stabilize these dens that were dug in loose, unfrozen soil. It is important that a bear chooses an area for his den that will remain stable throughout the winter and won’t collapse, but dens often do collapse in the spring and summer after the bears have emerged, and the bears are forced to dig new dens the following fall.
Before a bear digs and enters his den, he eats a large amount of food to build his fat layer. Berries provide natural sugars, and a bear may gain as many as 20,000 calories per day from eating berries in the late summer and fall. Bears also drink large quantities of water and consume foods high in protein, such as salmon. Brown bears add six to eight inches (15.24 to 20.32 cm) of fat before hibernation. They stop eating shortly before they enter their dens.
During hibernation, bears do not eat, urinate, or defecate. They curl up to conserve heat, but they may change position in the den. They are sensitive to their surroundings, and hey may awaken and move about or even temporarily leave the den. Pregnant sows give birth while in hibernation, and they can lactate to nurse their cubs. They can also lick and groom their cubs.
Bears emerge slowly from their dens in the spring. A bear may go in and out of his den many times over the course of several days before leaving his den for good. This is especially true of sows with newborn cubs who may stay near the den for one to two weeks, slowly allowing the small cubs to adapt to the outside world. Upon emergence, bears are groggy and sluggish, and it takes time for their bodily functions to return to normal. Soon after leaving the den, a bear will pass a fecal plug that may be as long as two feet in length (61 cm). This plug consists of digested food that has accumulated in the lower intestine as a result of not defecating all winter. After leaving the den, bears drink large quantities of water and slowly begin to eat new plant shoots.
Next week I will write about the amazing physiological adaptations bears employ during hibernation and how and why these adaptations are being studied by human medical researchers.