I've attached a couple scans of photographs I had published this month. One was a 2 page spread on a bear viewing article I wrote for Fish Alaska. The other were some bear photos to go along with a fishing story that took place in SW Alaska that appeared in the winter issue of Horns and Hooks. Scans don't have the quality I like but I wanted to show where your bear pictures may end up if you submit enough to editors.
HIBERNATION (or is it?)
Most of my discussion will be on Alaska's brown bears since that's what my customers are interested in seeing, but I've included information on all bears, even in my home state of Arizona for those more interested.
When do the bears go into hibernate?
That depends on the sex, but generally late October or early November. Pregnant females are the first to go in, followed by females with older cubs and younger males. The larger males are last and may not hibernate until late November or early December. Occasionally a bear will skip hibernation but that is rare in colder areas like Alaska. A male, or even a barren female may rise briefly for a few days during the winter, and some will even leave one den and dig another, but this is not the norm. Most bears stay in the same den and rarely rise unless bothered.
When they leave the den is the opposite with respect to order. Larger boars are first and may leave in April. The last to leave are sows with new cubs. They will be awake by mid May but she will probably stay in very close proximity to her den until as late as mid June. The rest of the bears will leave between the 2 extremes.
You may find it interesting that bears all over the world, including black bears as far south as Mexico will go into and exit their dens about the same time as brown bears in Alaska or Kamchatka. This certainly indicates a genetic component to it.
Where do bears den in Alaska, and what do dens look like?
Generally, coastal brown bears will den in the higher elevations on steep slopes just off the coast. They will dig a fairly substantial hole with somewhat of a tunnel and a "main sleeping room". The primary concern with den placement for a bear is to keep moisture out. If water does get in, they may have to leave and dig another.
In their dens, they build a nest. Studies done in Alaska found dens lined with alder and willow branches along with dried grass. You may think a bear den as a smelly musty area with all kinds of bones over in the corner, but it's quite the opposite. Since bears don't urinate or defecate when they hibernate they have a nice nest with dried vegetation and it can actually be quite nice. Although no one has been crazy enough to crawl into a brown bear den while occupied, it's frequently done by black bear biologists to check reproduction. In the 30 odd black bear dens I entered during my research I was always amazed how sweet they smelled and how clean they were.
Do they reuse the same den?
No, surprisingly not given the amount of work that goes into it. They do however have a strong fidelity to den in the same area each year and the new den will not be far from last year's.
Why do bears hibernate?
The fact that bears spend the winter hibernating is known by all school kids. But "skipping" the winter is not unique to bears. In fact all animals that are dependent on a seasonal food source, be it vegetation covered by snow, salmon that are no longer available, or insects that die must do something to survive a season of no food. Birds and some large mammals migrate to find their food. Bears don't have that option; there is nothing to eat during winter so they hibernate. They don't hibernate to skip the cold, although it probably helps. They have advanced hair that keeps them warm and a good layer of fat (blubber) that maintains their temperature. In good food seasons male polar bears are known not to hibernate, and in wet years black bears in Mexico skip hibernation because berries are available all year.
What happens to the bear physiologically when they hibernate?
Well, if you were to ask a hibernation specialist they would tell you that bears don't actually hibernate. So what you thought you knew from grade school is not entirely true. A specialist would tell you that bears go into long term torpor. In contrast, the arctic ground squirrel, a neighbor and food source for brown bears, is what they would consider a true hibernator. The difference being that bears don't allow their body temperature to drop but 6 to 8 degrees below normal (100 F, 38 C). Bears slow their heart rate from an average of 40 beats per minute (bpm) to 8 to 10, and there is a general slowing of all other the body functions. But the definition of a true hibernator is one that allows it's body temperature to drop to the temperature in the den. So in an arctic ground squirrel den, if the temperature drops to 34 degrees F, then that's the body temperature of the animal. They are" totally out of it", so much so that you can pick a true hibernator up, hold it, twirl it, anything you want as long as its humane and the animal is never aware of it. A torpid animal however does not allow its body temperature to drop that low, and one of the advantages, specifically for that of a bear, is that it can wake up quicker when it finds itself in danger and protect itself. When I visited those 30 odd occupied black bear dens I would have liked the bear to be totally out, they never were. In fact each and every one of them was looking right at me and was probably as aware as I was that there was nothing but 4 feet of solid air in between us. Yes they could move, and fast if they wanted to.
Another reason to maintain temperature is that pregnant bears have to keep their body temperature warmer. Remember, that the cubs don't start growing beyond the 300 cell stage until the female enters the den. If the female allowed her body temperature to drop to the just above freezing temperature in her den, then the young 1) would not be able to develop fast enough, and 2) they would likely freeze to death after birth since the mother's warmth and fur keeps them insulated against the cold temperature in the den.
Why would bears need to be aware when hibernating?
What the heck is going to crawl into the den, especially of North America's largest carnivore? Well, it does happen, much rarer today than probably historically, but more on that slight chance later (Can you guess what animal [not humans] might crawl into a brown bear den, kill it and eat it?) But behaviors we see today are a product of the species evolution, in other words their past. So from 500,000 to just 20,000 years ago brown (and black) shared their habitat with other large carnivores, larger wolves, large hyena like animals, a stronger cave bear, and large cats such as the sabre toothed tiger. These formidable creatures probably had the ability to take a brown bear while it was not hibernating, and certainly would have been able to when it was incapacitated. A bears ability to waken quickly and flee or try and defend itself would have an advantage over those that didn’t. And that's how natural selection works, those with traits that let them live longer and reproduce successfully have traits that become more and more common and end up "fixed" in the population. How often bears were killed in their dens historically is difficult to determine, but some bone remains found in caves do indicate it happened. And as humans became more advanced with better weapons (> 10,000 ya), indigenous people would take advantage of bears while hibernating as that was the easiest time to kill them, even with their ability to recover from torpor quickly. So today, bears do have an advantage by going "torpid" instead of hibernating as well as historically. OK, so what did you guess that is a current brown bear predator in its' circumpolar distribution from northern NA through Asia, all the way to Europe? As I said, it doesn't happen often because this predator is endangered, but in a recent brown bear study in Kamchatka, 3 radio collared female bears were killed and eaten in their dens by Siberian tigers. A 700 lb cat is just unfair! No animal has a chance against that.
Are you wondering why arctic ground squirrels don't do what bears do, keep their body temperature higher "in case of emergency". Then simple answer is they can't. Only animals as large as a bear can carry enough fat for the energy to stay at a warmer temperature all winter, a small ground squirrel can't. A bear can lose 25% of it's weight over the winter, a pregnant female may lose 40%, a true hibernator can't or won't. So ground squirrels have the advantage of not having to put so much weight on, but the disadvantage is if a weasel finds a way into their den, they are dinner.
What are some of the mysteries scientist may be able to solve by knowing more about bears hibernation?
Medical Doctors, endocrinologists, biomedical engineers, and others are all studying bears in hopes of learning more of their physiological adaptations. Understanding how bears survive and thrive in hibernation could have huge benefits for our species. They are particularly intrigued by how bears maintain their muscular and bone strength while immobile; the processes their kidneys, liver, and endocrine glands utilize to actually recycle waste products, and what substance or compound causes the bear to start the less dramatic form of hibernation.
Bear bone density does not decline while in the den, when in humans or most animals periods of disuse result in the lack of strength commonly known as osteoporosis. The recovery period needed in humans for the bone to regain strength is often 2 to 3 times the length of disuse. So spinal injuries, disease, or even space travel can result in reduced bone strength and increase in fractures, particularly in the large femur (leg) or humerus (arm). Bear bones do not lose their strength. Researchers know that during hibernation that the Parathyroid Hormone is higher, and that is an important part of bone rebuilding in mammals. They also know that one of the benefits of not urinating is that calcium is not lost, which is the principle building block of bones. Humans, or other mammals of course continue to urinate when bed ridden, and the elevated calcium ions due to bone disuse leave the body that way. Somehow the bear has a trigger that recycles the calcium, and triggers bone "rebuilding" just as if it were active.
Another key difference is that bears don't lose the muscle strength that you or I would when they are immobile. If you don't use a muscle, for a series of reasons it begins to break down and is known as muscle atrophy. If you or I were bed ridden for 6 months, the average human would lose 80% of their strength. Both brown and black bears have been tested for strength both pre and post hibernation and at most they lose an average of 10%. Imagine the benefits to us, or other animals if researchers could find how they retain strength during long bouts of inactivity.
At present they know 2 things are going on that reduce muscle atrophy. It does not matter if an animal is active or resting, the proteins in the muscle are slowly breaking down and need to be replaced, and movement helps the formation of the key muscle proteins. A byproduct of protein break down is ammonia, a toxic substance, which mammals quickly break down to urea. Urea is one of the key constituents of a mammal's urine because even though it's much less toxic than ammonia, it still can create problems if levels get to high in the blood. Since bears are not urinating, scientists were first interested in how high the levels of urea were and how much they could endure. From blood samples taken from hibernating bears, it was actually found that urea levels were slightly less than those of active bears which had researchers totally perplexed. It has since been hypothesized that bears use the waste urea and to build back proteins in the muscles. So as the muscle breaks down, it is rebuilt from a normal waste product that is not urinated. How exactly bears do this is not known, and the mechanism is of real interest to medical researchers.
A more recent discovery was made with miniature temperature sensors that were surgically implanted in wild bears before they hibernated. Sensors planted near the central body cavity showed the temperature dropped the initial 8 degrees in early hibernation, but never varied by more than one degree the rest of the hibernation period. Sensors planted near the skin however showed that temperatures varied from near freezing (the temperature of the den) but then would frequently rise again to the central body temperature. Although this may sound strange, you need to realize that not all parts of your body are 98.6. When you are outside and it's cold, your hands and feet and even muscles directly below the exposed skin are much cooler. This is normal until they get too cold and then the pain/numbness will force you to try and do something about it from putting on gloves to going inside to shivering. Hopefully that's possible for you, but for sleeping bear it's not. Researchers wanted to see how cool bear extremities (feet, exposed skin) could cool. From further study is was determined that on average of 4 times a day hibernating bears go through a shivering period where the muscles near the skin would move so much that they would produce enough heat for the body surface to warm back up to the body core temperature. Then they would stop shivering, cool down, and then warm up again. These bouts of shivering serve 3 purposes in a bear. They help the bear maintain it's whole body temperature from getting to cool, they keep the outer surface of the bear warm enough that there is no tissue damage during extremely cold periods, and they work the muscles enough that the atrophy is discontinued and the movement helps the rebuilding of key muscle proteins with waste urea. So by frequent shivering that does not cause them to wake and mystically using a waste product to rebuild muscles bears are able to maintain strength while hibernating.
The search for the compound that circulates throughout the bears body to slow it down, yet not completely, is an important and ongoing research project as well. In their search, researchers have dubbed the still unknown compound as Hibernation Induction Trigger, known as HIT. Their hopes are that if they can find this substance, it could be crucial in slowing down the decay of organs used in transplants. At present, an organ lasts about 16 hours before tissue deterioration makes them unusable. It is hoped that HIT might increase the life of an organ threefold, so we could all benefit from the physiological secrets of a hibernating bear.
In my Animal Physiology class, I have several Pre - Med students that at first just can't seem to understand why we have not learned more from the bears. Why with such possible human benefits has bear hibernation been more well studied, causes identified, and cures for humans developed? The answer is relatively simple, bears just don't make good laboratory subjects and are not easy to get to in the field. A wild bear will not allow you to visit several times to take the samples that are necessary to solve such complex questions. They have tried with captive bears as well, but they are still large and powerful, and not really tame in the sense of a dog. Plus captive bears often change their physiological status due to continued interruptions, and captive bears often go through a much lighter torpid or hibernation phase, or if well fed, don't go into hibernation. As more sophisticated micro electronic sensors that can be implanted in animals are developed, researchers may be able to learn much more about how bears can do things that other animals, including humans, can't.
So there is literally a wealth of information to be gleaned from even a torpid or hibernating bear.
I went for a scouting trip to Bosque del Apache in December for just a couple days but was very happy with the images I took in such a short time. It was crowded as the week before Christmas is a popular time for many of the tours but my fellow photographer and long time friend Bruce Taubert had an excellent time. Birds are back at the major roosting pond for the evenings and the magnificent fly outs, not in huge numbers as they are roosting in other ponds as well, but it still made for a nice fly out. The sunrises were spectacular as you can see below. The colors there never cease to amaze me and I slightly desaturated the images below as the red was overwhelming. There were approximately 65,000 geese there, 7,000 sandhills, and over 40,000 ducks of various species. As usual the northern pintails were the most numerous. The fly in to the major roosting pond by the sandhills was different than I have ever seen it before and it provided some great opportunities for flying birds. They were coming in from the east so you could set up on the west shore and get some excellent shots with the front of the cranes completely illuminated by the softer late afternoon light. I was dissapointed I only had one afternoon to shoot them in this light, but I still have many photos to process so I should not complain. Bruce and I headed to Albuquerque where he met his tour group and we all went to the zoo to shoot wood ducks, many to choose from at quite close distances as usual. The next morning I skipped the zoo in search of an area I might be able to photograph flying wood ducks and was lucky enough to find a few. Shooting flying birds is always tough and these little guys average around 45 miles per hour. I was able to get a few landing that I'm happy with but just didn't have the time to get a side view. I had to get back to work and make a Christmas shopping stop in Gallup which both my wife and son appreciated less than a week later.
In this new year I have many exciting photo trips lined up including south Florida, High Island in Texas, a few more trips to Bosque, my annual brown bear shoots in AK, back to Colorado for leaf color changes and elk again, and the pinnacle, 6 weeks in South Africa as I design a study abroad class on Wildlife Biology for ASU. I'll also have several local trips lined up. This late winter, early spring I hope to center on waterfowl, smaller predators through calling, and the desert breeding birds as the season is just around the corner. Happy New Year and Happy shooting to you all. I hope you feel as blessed as I do!
Here is the press release from the Boyce Thompson Arboretum:
Marvels of Migration Photography-Lecture By Stan Cunningham Dec. 9 Last winter Arizona birders and photographers were surprised when a wayward Common Goldeneye spent a few days at Boyce Thompson Arboretum State Park, near the scenic copper-mining town of Superior, about 45-minutes drive due East of Mesa. Would you believe that of the 850 bird species in North America, more than 300 leave the continent and spend the winter in Central and South America and the Caribbean? In preparation, some transform themselves into “super birds”: gorging until they accumulate fat reserves that almost double their body weight in order to have the energy for transcontinental flight? Others take an opposite approach - flying just a few hours each day. And how do they find their way? An internal magnetic compass, eyes that can see polarized light or even magnetic directions, memorized celestial maps along with many other methods have all have been hypothesized and some convincing data collected. Research biologist and ASU Polytechnic Wildlife Professor Stan Cunningham will share these and more insights into avian migration during a lecture Dec. 9 at Boyce Thompson Arboretum accompanied by his impressive photography of birds on the wing. The presentation begins at 1:30 p.m. in the lecture room of the Smith Building and is open to the public, included with Arboretum daily admission of $9, and no pre-registration required. For the past three decades Cunningham has lived an adventurous life you'd expect to see depicted on film: crawling into black bear dens during wintertime as a wildlife biologist for the Arizona Game & Fish Department and spening a month each summer in Alaska as a professional photographer, shooting vivid pictures of Brown bears for magazines, tourist lodges and leading Alaskan photo safaris and ecotourism trips. A professor of wildlife biology at Arizona State University Polytechnic since 2006, Cunningham is known for his decades of research about bears, mountain lions, and the ecological effects of wildfire. On Sunday, Dec. 9, he will share some of the secrets scientists have learned on migration and navigation along with some of his most breathtaking avian photography.
I also will be talking about photographing migrating birds. I hope to see you there.
My passion for wildlife is so great I rarely make the time to get out and photograph the beautiful scenery here in AZ. I've made a pact with myself to change that this year and I've joined a couple landscape oriented photo groups for encouragement. A couple weeks ago I found myself in the Westfork of Oak Creek Canyon near Sedona to try and capture the colors and reflections of the turning maple trees. It was a wonderful day with bright colors every where. I found myself frustrated however as there was so much beauty over such a wide area I found it difficult to capture it with a camera. It wasn't until I got really serious with photography that I realized what a wonderful filter and exposure meter the human eye and brain is. Even with the wonders of modern digital today's cameras can't do that and I suspect never will. It was a wonderful day and I do look forward to going back next year, and I will need to bring Lori (my wife) along as she was pretty jealous of my opportunity. I also think she often has a better eye for color, light and landscape shots than I.
One of favorite things to do in the fall is to head to the high country when the elk are in rut. The sounds of the bugles reverberating through the mountains all night long is music to sleep by. And to have the opportunity to chase and "talk" to them with my selection of calls is as exciting as anything I do with a camera.
This year my scouting over the past few years in Arizona paid off with some great photos. And additional trip in northern Colorado to the Rocky Mountain National Park paid even bigger dividends. For 4 1/2 days I hiked and drove through the park in search of elk. They were not hard to find, especially if you were willing to walk a little. I did realize it had been a while since I've worked at 9,000 feet though. I had to delete a few nice video snips I took because of my hard breathing that was recorded when filming the video.
But I've posted a couple on You Tube and you can see one of them just below.
I was also hoping to hit the aspen turning at the same time but I was about a week late. It still was beautiful and I've posted some of my elk and landscape photos from this fall below. I hope you enjoy them. I sure enjoyed taking them.
And in case you are wondering I'm already working on finding good accomodations for taking a photo natural history tour to Estes starting in either 2013 or 2014 at the latest.
Coastal brown bears are one of the largest land carnivores in the world with males weighing up to 1500 lbs. On average polar bears are larger but the largest bear ever weighed was an Alaskan brown bear over 1800 lbs. This guy is probably a mere 1000 lbs, and will probably be 200 to 300 more after the salmon season.
This sow is probably just over 500 lbs while her 2 cubs are near a 100 lbs at 14 - 16 mos old.
How large do Coastal brown bears get?
The size of course depends on the age and the sex of the bear. A brown bear male (also known as a boar) is usually fully grown at 8 years old, and gains about 100 lbs a year from 3 to 8. His final weight will be from 800 - 1000 pounds, but brown bear males over 1500 pounds have been measured. A female (aka sows) usually stops growing at 5 years old and weighs about 350 -500 pounds midsummer. Both the male and female can easily gain a couple hundred pounds from early summer to late fall when they go into hibernation. An interior brown or grizzly boar could range from 500 up to 700 (but that's very large) and a female will be from 3 to 500 lbs.
Why are the Coastal Brown Bears larger?
The larger predictable supply of the vegetation and berries growing along the coast helps, but it’s primarily the salmon diet that helps them attain and keep a large size. Not only are coastal brown bears up to twice as large as inland browns, their populations are up to 10 to 20 times denser than interior populations, another facet based on the abundance of food. Females tend to have larger litters and are more successful at raising them. The predictable supply of the high fat/protein salmon diet gives them a tremendous ability to succeed.
At an average of 4000 calories per fish stored, this is when the coastal brown bears really put on the weight, eating from 10 to 50 fish/day
When do the bears begin to eat the salmon?
The answer to this is easy, but not exact. It's as soon as they can! Bears seem to have an uncanny knack for knowing when the salmon begin to run and will show up within a few days, often congregating at shallow spots along the creek where it is easier for them to catch the fish. Depending on the geographic location in either Katmai or Lake Clark National Parks, salmon may be available as early as late June or as late as August-September in other areas.
How many salmon does a bear eat a day? Do they eat the whole
The short answer to both questions is it depends. How many salmon they eat depends how many they can catch, and how large of a bear they are. If the salmon are numerous and each bear can catch the number of salmon they want, they will catch somewhere between 10 and 20 a day, but large males have been seen catching and eating as many as 50.
Each salmon is roughly worth 4,000 calories in entirety, and 20,000 calories ingested a day is common. In the height of a salmon run, bears are estimated to gain from 2 to 4.5 lbs in fat a day. That’s very important for that winter hibernation period. If the salmon numbers are high, and the bear is skilled at catching fish (something they get better at with age), bears are known to switch to just eating the fatty parts of the fish. Fat has twice the calories of protein, so it's possible to see a bear just eat the brains, the skin, and the eggs if it's a female salmon. They may lay that carcass down and then go get another. Although you may consider that wasteful, nature won't allow it and the red mass of protein will be utilized later by less skilled bears, cubs, or even other species such as bald eagles, gulls, magpies, or even other fish like the dolly varden that follow the salmon.
This large bear is skinning the just caught salmon. When the fish are really running in large numbers some good fishing bears may only eat the skin, roe (eggs), and brains. The rest does not go to waste however, and the waste is quickly devoured by less skilled fishing bears and/or eagles and trout waiting near by.
Before I start this particular blog (or chapter may be more appropriate) I think it's important to point out that the life of a bear could be defined as a race. Each year is a race to put fat on before there is no food and the bear must hibernate. When they enter hibernation they have to count on the fat reserves they were able to store over summer. If there is not enough fat they could die during hibernation, or during the following spring before the summer growing period starts.
A female will only produce cubs if she has enough fat reserves when she goes into hibernate. Years of poor vegetation growth or salmon runs are followed by years of little to no cub production. A study of Katmai brown bear females found that they averaged losing 150 lbs when hibernating (approximately 30 to 40 % of their fall weight), most of which was fat. They need to get all of that back each year.
The questions below are one's I commonly receive so I put this blog in a question and answer format. I hope you enjoy reading it!
What do bears eat?
Coastal brown bears have access to 4 different food groups: 1) vegetation, 2) clams and other intertidal invertebrates, 3) berries, and 4) the food item they are most associated with, salmon. Vegetation is the most available, and green areas along the tidal zone appear first (as early as May 15). These early green ups are critical for bears emerging from dens that have lost so much weight.
What type of vegetation do the bears eat?
They won't graze on all the plants but brown bears have been recorded eating over 200 plant species so they are probably much more herbivorous than you thought. Goose tongue and arrow grass are some of their favorites in the Lake Clark National Park area.
The vegetation itself benefits from it's coastal location. First, the warming effects (just above freezing is warm for coastal Alaska in April-May) allow these zones to be the first ice free areas and the plants begin to grow. Second, each time the area is flooded with high tides it's essentially fertilized from nutrients in the water from the ocean. The slow retreat of the tide allows the vegetation to capture additional large particulates that adds important nutrients. A high tide essentially fertilizes the vegetation, and the bears take advantage of the extra growth and essential nutrient the plants provide.
Do bears digest vegetation as well as a cow?
Even though they seem to graze like cattle, bears are not near as efficient as extracting calories and nutrients from vegetation as a cow. One research model predicted that a brown bear must eat for at least 12 hours and ingest 20 lbs to just maintain it's weight This large amount of forage is necessary partly because of their poor ability to digest vegetation and partly due to their large size. There have been numerous studies with conflicting results on how bears fare as herbivores, which is the most common part of their diet when salmon are not available. Interior bears may eat up to 90% vegetation in a season, but most coastal bears switch to more nutritious salmon when they begin to show up. Most studies found emerging coastal brown bears continue to lose weight after hibernation at least until the vegetation green up occurs in Mid May. Most scientists estimate they maintain the weight after the green up by grazing, with maybe some minor weight gain. It's obvious that coastal brown bears must have access to more nutritious sources to put on weight, and reach their large size. As a fellow photographer I know the frustration of following grazing brown bears that seemingly never lift their heads. And Murphy always rules as their head seems glued down when you get that rare sweet light. I do ask however that you remain patient and not disturb the grazing bears. All that effort they are putting in for up to 12 hours just to maintain weight is a lot, and we don't want to negatively affect them by scaring them and reducing that valuable grazing time. They will pick that head up, just be ready!
Berries can be important very early or late in their active season. The high sugar content can be crucial to provide the extra fat, especially after the salmon run, that bears need as they near the end of their race to regain weight in late fall. Key berries in Katmai and Lake Clark that brown bears consume include blue berries, salmon berries, elder berries, and nagoon berries. Berry crops not eaten the fall before also may provide forage just after hibernation if not covered by snow and ice.
Are the bears really clamming out at low tides?
You bet! Along the coast, many bears will hunt for the clams uncovered during low tides. The majority of clams eaten on the Alaskan coast are Pacific razor clams. Studies of Alaska bears found they like razor clams, soft shell clams, and a few types of molluscs, and polychaete or tube worms they find in the sand. They probably use all of their senses to find them as they walk around with their nose close the ground. Smell, vision, and even feeling the clam move though it's paws make them so successful. A study where bears were observed clamming on 233 days over a 3 year period found that the average bear ate a clam almost each minute it foraged. Many ate from 50 to 100 in the short periods the tide was low enough. Researchers found some bears are right or left pawed, but I've seen the same bear use both. How they break and extract the clam from the shell can be different between bears as well. Clams are only available for a few hours and only about 15 days a month when the tide is low enough to expose them so not all bears use them. However, they provide another important pre salmon food source, which contains 3 times the amount of protein as a similar amount of vegetation. One study found that a brown bear that ate 50 - 100 clams in a couple hours was able to reduce it's necessary grazing time by 25%. As I mentioned above, this valuable time could allow her to add more fat, and be more successful in making sure she can make it through the winter.
Why don't more bears make use of the clams that are exposed during low tides?
That is an excellent question and not one easily answered. Observations of clamming bears throughout the coast discovered 2 key points, sows with cubs are seen clamming more than you would expect based on their numbers, and large boars are rarely seen on the beach. In fact, in the study above, 45% of the bears observed were females with cubs, and 55% were "unidentified gender and smaller (< 500 lbs) bears". Why large boars don't frequent beaches given the higher protein content is unknown. Some scientists hypothesized that because of their large size, the energy required to walk that far for a smaller amount of food may not be worth it for a large boar. Why females with cubs are found more seems fairly easy to explain. First, lactating females need more and richer foods, as do their rapidly growing cubs. Second, for a Mother bear to find an area to forage where the main cub predator, large boars, is absent makes life easier on them.
I've posted over 70 new images I took on the Katmai 2012 trip. You can view them just under the description for the 2013 Katmai trips to see what kind of opportunities await. Or you can click here to see them on Flicker but note I keep the size of images small due to photo theft so if you enlarge them too much they won't maintain their quality. Drives me crazy but I've had one photo stolen and don't want it to happen again.