The ultimate role of the Polar Bear as the most powerful predator of the sea Ice is what defines its importance in the ecology and evolution of the arctic marine ecosystem. The ringed seal is the primary prey for polar bears. It is the largest and most widely distributed seal in the Arctic. However, the adult ringed seal weighs only 4070kg (90-150 Ib). Polar bears appreciate the small size of ringed seals. It allows small bears to successfully hunt them down and kill them. Ringed seals can be found as one animal or in small groups throughout large areas.
Arctic sea ice
While polar bears can hunt seals at any time of the year, they prefer to be on ice during spring and summer. Winter and spring are when adult ringed seals defend their territories below stable frozen landfast and interisland channel ice.
These seals are spread over large areas in winter and spring at relatively low densities. Seals need stable ice to breathe because they use their heavy claws to remove refreezing ice from their foreflippers. If one uses a hydrophone (an underwater microphone) to listen for the vocalizations below the ice of seals, the most common sound is actually the periodic scratching of nearby seals as it keeps a breath hole open. Access to breathing holes is crucial in order to avoid damage from unstable ice. Seals are able to pack ice. Bears can easily capture large areas of ice when they come to the surface to breathe. Ringed seals have multiple breathing holes and other openings, along with pools of water or along leads. This means that bears cannot anticipate where their prey will appear next. The snow-like, windblown, rock-hard snow that forms over seals breathing holes provides some protection. Ringed seals reach up through their nostrils and pull out small haul-out lairs from the snow drifts. They can then rest. In spring, single pups are born to pregnant females in these lairs.
Born around April 1, ringed-seal pups weigh in at 5.5 kg (12 Ib) and are approximately 12 Ib at birth. After six weeks, the pups are weaned. They weigh approximately 22 kilograms (48 Ib) and have gained approximately 0.43 kg (1.9 Ib) each day since birth. The seal pups born in spring are the fattest. These pups have not yet been exposed to predators. They are most vulnerable to the bears from the moment they are born until the ice melts in summer. The ice is the only way for polar bears to hunt seals. Although seals can be killed by bears at the shoreline, hunting success in open water is uncommon. Seals can swim faster than bears and swimming is more efficient than walking on ice.
Many bears, especially adult females with newborn cubs and/or subadults, move to stable landfast areas close to the coast or deep bays for hunting by April. For smaller and lighter bears, it may be more difficult to penetrate the hard snow covered with seal liars. Because adult males can sometimes kill and eat both cubs,
Young independent bears and their habitat may be used to decrease the risk of being preyed on by other more vulnerable bears.
Even between localized areas, success rates vary greatly. Overall, however, it seems that while polar bears may sometimes travel long distances in hunting seals at their birth and haulout lairs for seals, they have relatively low success rates overall. Below are some examples. We followed bears for several thousand kilometers during a three-year period with high seal productivity. Only 48 (7.6%) of the 556 attempts were successful. Then followed a low-seal productivity period. Scientists traveled similar distances, but only 120 attempts were made in the same area. This confirms our findings from other sources about seal productivity. 8 (8.7%) of these attempts were successful. This indicates that, even though the productivity of seals was low the success rate of bears at their birth lairs was comparable. After 172 attempts to capture the pups at their lairs, 11 (6.4%) killed bears were captured over several hundred kilometers. While the majority of kills were pups, there were some adults and subadults as well. A polar bear will appreciate capturing a fat female seal prior to she starts nursing a pup.
Tom Smith trained dogs to find subnivean (below-snow) lairs of ringed sea seals. He used this information to determine the quality and importance different sea ice areas for breeding habitat. The importance of subnivean lairs in protecting seals against predation is further revealed by Smith’s record of the number of lairs that bears predated. Smith and his dogs discovered 310, 363, 239 and 239 lairs in Amundsen Gulf (SE Beaufort Sea), the High Arctic and southeastern Baffin Island over a period of eight years. Bears had dug into five (1.6%), 110 (30.3%) and 47 (19.6%), respectively. The bears made kills at 37 (23%) of 162 lairs.
Predation of Marine Mammals and Seals
Bearded seals are the other major prey species of the Polar Bear. They are much bigger, but far more abundant than the Ringed Seal. The name “bearded” comes from the large whiskers it uses to hunt for food in the bottom of ocean. Based on the rusty faces of some people, it is believed that they often delve into the bottom sediments in search for prey. Adults can weigh anywhere from 225 to 360 kilograms (500-800 lb). Large bearded seals are often killed by large male bears. Smaller bears can however benefit from the remains of kills and may capture younger seals. The Arctic is home to many bearded. They are found in areas where pack-ice is overly shallow. Although they can maintain their own breathing, like ringed seals, I prefer them to do so. They usually remain in drift ging packice, which is typically found over shallow water.
In certain areas like Davis Strait, the Labrador Sea and the Labrador Sea in March, harp seals and hooded ones make their way to the pack ice to give birth to their pups. While hundreds of thousands of seals can be present at once, most of them stay there for just a few days. There is a risk that a bear might hunt too far from land, on ice floes, which can easily break up at any time, but the caloric benefit of having so many pups on the surface of ice is immense. Many polar bears travel hundreds of kilometres from southern Baffin Island to feed and then continue walking north across the pack ice, which is constantly being carried further southward by the Labrador Current. Polar bears may also hunt harbour seals that are found in areas with pack ice where they can be seen around the leads or taken out to seashores during the open-water season. However, harbour seals do not appear to be abundant in most areas where polar bears live and they probably don’t account for much of their annual energy requirements.
There are some areas where polar bears can also kill walruses. These include the West Coast of Alaska, in the Bering, Chukchi, and Canadian Arctic Islands. The adults are too large and protected by thick skin, so only smaller and younger walruses can be successfully preyed on. It is only the adult males of polar bears who are capable to kill walruses. Sometimes, walruses will panic when they are approached by polar bears. This can lead to them running to the water, sometimes leaving their young or pups in danger. Natural causes may also be a problem in areas where there are many walruses. Sometimes, different sizes and ages of bears may find the same carcass.
Another dramatic situation that is less common but still quite common is when belugas whales (sometimes called “white whales”) become trapped in a small, enclosed pool of water. The water is surrounded with solid ice and there is no escape route. In Greenlandic, this type of entrapment can be called a “sassat”. This is a common occurrence in the Arctic. These situations can be caused by large male bears harassing the whales as they come to breathe. Eventually, the bears become tired enough to take one of the bears with their teeth and claws, and drag it onto the Ice, where many bears will then be able to feed at the same moment. Biologists from Alaska discovered a spot where polar bears had pulled more than 40 belugas onto the ice, in an amazing example. Similar entrapment occurred in Jones Sound in Canada’s High Arctic. Polar bears trapped 20-30 whales and exhausted them until a large male was strong enough to grab hold of the weak animal and drag it out onto the ice. Many gulls and bears ate the abundant carrion.
Beluga whales are found in the Arctic. In summer, they go to the mouths of rivers, where the gravel bottom helps them remove their skin. Cunningham Inlet is a coastal area on Somerset Island in the High Arctic. Because the water is often very shallow, especially at low tides, it’s possible for a whale to become stranded there for hours or even days until the next high tide. Tom Smith and his collaborators have documented 10 cases of strandings over nine years of monitoring belugas in Cunningham Inlet during summer. This can sometimes happen with up to three whales at once. These whales could have been preyed upon by bears if they had been present.
The same time, scientists studying polar bears witnessed four unsuccessful attempts to capture belugas from shallow water. Two of the three attempts were made by the same large male bear that was hunting from drifting pans. Both cases involved young calves measuring 200-250 cm (79 to 99 in) in length. They were caught by the bear lying on an ice floe. The calves then swam close enough that he could jump onto them. After that, he was able to hold onto them long enough to lift them off the ice. A second occasion was when a scientist was flying over another High Arctic estuary to observe eight polar bears as well as several whales. The bears had taken five belugas, four narwhals, and a calf. Two of the adult female Narwhals were still breathing and had been pulled 150-200m (490-666 ft) inland to stop them from running back into the sea. These remarkable observations prove that bears can learn to capture narwhals and belugas when given the right circumstances.
Despite the regular appearance of belugas in estuaries like Cunningham Inlet every year, it seems that not many bears have learned to exploit this situation. Polar bear scientists only recorded 24 bear sightings in nine seasons. Most of them were young animals too small to be able to kill large mammals like the beluga. Over the years, only a few successful predations on belugas and narwhals were reported in Arctic. This, along with the fact that two of the most successful hunts of whales on water by polar bear scientists, suggests that most whales are too large for most polar Bears to be able capture them on a regular basis.
Whales are most likely contributing the most to the diets of polar bears by bringing in animals that occasionally die from natural causes. These animals can then be washed up on beaches, where they can be scavenged by polar bears of all sizes and ages. For local bears, larger whales, such as bowheads, sperms, minke, fins and fins, can offer abundant food that lasts up to a year.
Polar Bears Eat a variety of Foods
The collective observations of Inuit hunters as well as scientists, eco tourists and explorers over many years have provided a wealth of information on the species of marine mammals that polar bears consume. Anecdotal and observational observations of hunting bears as well as the interpretation of their tracks in snow have revealed a lot about how bears capture different species. Although we were aware that bears hunt a wide variety of prey, it was difficult to estimate how much each species could contribute to the diet. However, most people agree that ringed seals are the most important prey.
Greg Thiemann, a researcher, has recently examined the fatty acid content in the body fat of Polar Bears. He discovered a number of interesting new details about how varied the diets can be for polar bears with different sexes and the differences between bears living in different areas. For a long time, it was known that fatty acids in animals’ adipose tissue (fat) tissue can be derived directly from the food they eat. Polar bears can digest fat at 97%. The simple idea is that one could analyze the fat and determine what it had eaten. Additionally, it is possible estimate the nutritional contributions of each species. Bears store fat on different parts. Therefore, it was crucial to find out if different fat samples gave the same results. It was amazing to see that regardless of the location, the results were identical. This allowed us to analyze specimens from bears killed by Inuit hunters and immobilized for research.
Thiemann used fat samples taken from polar bears in several areas to confirm the species that they were eating and also assess their relative importance, both within one area and across seasons. For all the areas shown here, as well as those not included in this survey, the generalization that ringed are the most important prey species still holds. The importance of other species is highly variable, even bearded seals vary in their importance in different areas. There are many things we can learn from the high importance of belugas in certain regions. For example, how much may come from the direct hunting of bears and how much from the scavenging of naturally dead whales.
Davis Strait had the highest prey diversity out of all the areas. It was not surprising that harp were more significant in Davis Strait due to their >6 million population and the fact = that they mainly breed in large numbers in spring to give birth to their puppies in predictable places. The bears’ diet was about three-quarters of that of harp seals. Although harps seals are less common in winter, their presence is still significant. They accounted for 15% of the diet, which is higher than any other recorded species. In summer, harp seals can also be taken by polar bears north of Svalbard. However, it isn’t known what portion of the diet they consume.
Canada has hooded seals that are only available to polar bears in Davis Strait. These seals form when they gather on the ice to give rise to their pups. The two small areas where they do this for a few weeks in March are off the coast of southern Labrador, and near the southeast Baffin Island. After the pups are weaned the entire population will remain primarily pelagic on the Greenland coast. Polar bears cannot reach them there once they’re older. The diet included only 2-3% of hooded seals and was more important in spring than it is in winter. However, the inclusion of hoodeds seals in bear’s diet shows that bears have a good understanding of where and when these animals are available. They also know how to make concentrated use of them for short periods of time. The adult male and female male hooded seals can be large and aggressive so they are often killed by large male bears. The pups are weaned in a shockingly short time, only four days. The pups are free to roam the sea ice on their own, and they don’t fear predators. It seems that bears of all ages and genders may selectively hunt their pups. These are highly vulnerable and extremely fat after weaning.
Thiemann’s research in Foxe Basin showed that walruses are still more important to bears than the four other species of seals. The most important prey species was still the ringed seals. Other areas that have walruses, such as Baffin Bay and Davis Strait or Lancaster Sound, only small amounts of their diet were available. This is consistent despite the fact that polar bears have difficulty killing them. The walrus likely gets their food from eating dead animals.
While not illustrated, the ubiquitous ringed and bearded seals are the most important prey in both the southern and northern Beaufort Seas. Bearded seals in the southern Beaufort Sea are more prominent than those in the northern areas. This could be because they have greater access to their preferred habitat of pack-ice that lies above the shallower water of continental shelf.
Polar Bear watching
While we did learn a lot from watching bears hunt and their tracks in the snow, talking with scientists and Inuit ha hunters, there was nothing more informative than just simply watching them for weeks. It was a simple act of watching the animals hunt and listening to their stories. Radstock Bay provided a unique opportunity to understand how wild polar bears live.
Hunting Seals in the Sea Ice during Summer
Bears will wander along packs of ice in summer to find seals. Their huge heads swing from side to side while they walk, giving them the impression that they are completely unaware of their surroundings. If given the choice, bears will usually choose to move towards or across the wind. This probably allows them to sense a seal’s scent and detect it. Sometimes, bears will stop to look around and raise their noses to feel the wind. It is easy to miss the little things, despite their casual appearance.
While their eyesight is comparable to that of a human, it is their keen sense of smell that they use for information. Like an invisible code that identifies a location to hunt on ice, their sense of smell tells them if bears are upwind and if there is a seal carcass for them to scavenge from, or anything else that might be interesting enough to warrant investigation. As these animals become more complex, one can see that there is nothing casual about them. Their entire existence is based on hunting and energy conservation. They get energy as efficiently as they can and then expand it as sparsely as possible between meals. If you’re patient enough to look closely, their actions and how they behave over the course of a day, or week will show you what it means being a polar bear.
If a bear has seen a seal sitting on the ice or heard it breathing, or because of its extraordinary sense of smell, it may choose to hunt in a particular spot. The strong fishy smell of seals can leave traces on the snow or ice. Bears may be able to tell if a seal has been there recently by their strong breath. Due to the constant threat from predation, ringed seals often have multiple breathing holes or alternate locations along leads or pools of open water. Radstock Bay long-term observations revealed that ringed seals may move from one location to another to make their movements more predictable to a s bear. Sometimes, bears will pass a spot quickly. We knew that a seal had been there and stopped hunting. It was apparently aware of a location where there is a greater chance for a seal to surface to breathe again before moving on. We were often very baffled to witness a bear hunt at a certain spot.
Two basic methods are used by polar bears to hunt seals on the sea-ice in late spring and early summer before it breaks down: still-hunting or stalking. The most popular and thrilling method to observe is the stalking a seal that has been pulled out onto the sea ice. It can be done when the bear and its prey are fully visible. The weather should be warm enough to allow for the seals to stalk. When a bear first sees a seal lying on ice, it begins planning for a stalk. This is usually at a distance between a few hundred meters and a few hundred metres. Instantly, the uncoordinated walking stops and the bear stops. Sometimes it freezes in mid-step just like a bird dog. It stares intently at its seal, standing motionless. Sometimes, the bear will stay still for several minutes to assess how close it can get to the seal in order to make a final charge. When the bear starts to stalk the seal it will lower its head and walk slowly and steadily toward it, sometimes in a semi-crouching position as it approaches. When basking on ice, ringseal seals are usually on alert and raise their heads to check for potential predators. Inuk hunters will not move if a seal is being stalked by them. Instead, they will keep their heads down until it falls back. Curiously, however, polar bears don’t do this. It just keeps moving slowly, steadily, towards the seal in as straight as possible, while keeping its head low. This position makes it’s dark nose and eyes more visible. It charges quickly to the seal within 30-40 m (100-133 ft) of the prey. The terrified ringed seals bolts for its hole in panic when the bear reaches this distance. Ringed seals often go on their own to find a place to breathe. It is not difficult to understand why. When there are more than one seal within a single breathing hole (which is often the case in late spring when a female might still be accompanied with her pup), they can become incompatible when trying to escape from a charging bear. This gives the polar bear a quick advantage to reach one seal with its claws and teeth. After grasping a seal, the bear quickly bites its head several times before pulling the carcass from the hole. Sometimes, this can take up to 100m (330+ ft) before it begins to eat it. This ensures that the seal does not escape and is actually dead.
A few bears have a specialization in what I call the aquatic stalk. As with the bears that follow the 5th seal across the ice surface, the aquatic stalk seems to help them remember the route before they enter the water. There are two types: one is the aquatic stalk. The first is when the bears swim under water between holes in the ice, or along the edge an ice floe. They breathe so stealthily, that only the tip is allowed to touch the water. The bears move closer to seals to make their surface breath. My longest time between breathing holes was 72 seconds. Finally, the bear has reached the seal’s last breathing hole. The bear then disappears from view. After an eternity filled with suspense, water in front seal explodes. The bear then uses its powerful forelimbs immediately to jump onto the ice and catch its prey. The seal often manages to escape the lethal claws, and reach the water where the bear can easily outswim it. In one case, I witnessed a bear chase a bearded seals from a distance over 300 m (985 feet) but it missed the seal by less than a metre within the final seconds. Because the seal appeared to be nervous, it may have seen him come up through the water. The adult bearded seals are big and powerful and can spin and escape into the water even with a partial hold.
In areas like Hudson Bay and Foxe Basin on the eastern coast of Baffin Island the sea ice completely melts in late summer. This forces bears back to the land to wait for the sea temperature to rise. Since ringed seals don’t tend to be able to haul out on the ground, they are more agile in water than polar bears, this makes it difficult for them to hunt seals. Young bearded and harbor seals often rest on sandbars at the mouths of rivers. However, bears occasionally capture them from rocks or along the coast.
Hunting Seals in Open Water
A bear has caught a seal in the open waters. This is an interesting and unusual observation. Don Furnell, a Northwest Territories Wildlife Service biologist, and David Oolooyuk an Inuk hunter were watching a large, adult male Polar Bear swim in relatively shallow waters near Wager Bay in northwestern Hudson toe- Bay. At 75 m (254.5 ft), a ringed sea seal was visible swimming in shallow water near Wager Bay, northwestern Hudson toe-bay. The seal seemed to be alternately diving to feed on itself and surfacing when it needed to breathe. The bear flew towards the seal’s surface. The seal swam towards the bear and took a deep breath. However, the bear was still motionless in water. Finally, the seal was only half a metre away. The bear managed to reach the bear and lunge at it, biting its back. They saw a male swimming with a dead sea seal in its mouth several days later. They thought that the seal could have been swimming near a dead seal in the water, as its colour would make it believe it was a small piece of ice. This is plausible. Biologists and Inuk hunters are well aware that seals can be attracted to pieces ice during open water season. This may be because they feed on invertebrates or small fish living in the channels under the ice. Small pieces of ice are often used by seals as a place to rest and haul out their cargo. Furnell, Oolooyuk and others did not know whether more than one bear was hunting in this way. However, they reported seeing some other fresh seal carcasses at the beach. It is possible that this hunting technique was learned from a small group of bears. The lack of similar reports from other people in the Arctic suggests that polar bears are not successful at hunting in open water. This is despite the fact that many people visit coastal regions for extended periods of time every summer.
Still-hunting in Summer
After the snow melts from the ice surface sufficiently to permit seal breathing holes and nar1 row leads in ice to be visible, the main hunting technique for polar bears is “still-hunting”. The bear waits for a seal’s surface to breathe while sitting, standing, or lying motionless near a breathing hole or the edge of J. A lead. The most common of these three methods is lying still hunting. This is because the bear uses very little energy while waiting for prey. After spending considerable time watching bears hunt, we were able 5 to identify them.
This was the main method of hunting. It is possible that early explorers and naturalists may have believed that a distant bear lying on ice was asleep, but it was actually actively hunting in the most efficient way. The amazing nature of a stalking hunt with a last-minute charge was probably the most well-known type of hunting that was described in early writings. It was also not surprising that lying-still was so rarely used. It is common to still hunt by lying on your stomach or chest, with your chin close enough to your mouth. It is vital to remain still when hunting in breathing holes. Seals are very sensitive to noises and will flee to safer places if they hear any. I was able to test the transmission of noise from snow-covered glaciers by inserting a hydrophone into water through a seal breathing hole, and then making a series grading of disturbances. The water immediately emits a loud, scratchy or crunching noise from my boat when it moves on the snow or ice surface. A person’s or a polar bear’s walking sound can be clearly heard up to 400m (1300 ft). It is no wonder that a polar bear has to remain still!
Although most still-hunts last no more than an hour, there are some that can last up to several hours. Another reason bears like to save energy is to lie down where they are less likely make unintended sounds. A seal might also see the advantage of lying down, as it presents the lowest silhouette to the sky.
A seal’s appearance to breathe instantly transforms the scene from one of peace and quiet into one of action. In one movement, the bear grasps the seal’s head or upper bodies in its teeth, flipping them out onto the ice and letting them wiggle about like a fish just pulled from the stream. The bear then begins to eat by biting the seal around its neck and head several times.
Seal hunting in winter and spring before the snow melts
In cold weather, seals rarely venture out on the ice. Therefore, almost all hunting is done by still hunting: waiting for the bear to approach the seal. Seals will breathe wherever there is water. Seals will continue to breathe in cracks in ice until they freeze. This is because it’s easier, requires less energy and doesn’t limit their movement as much. Seals must ensure that their breathing passages remain open after the ice has frozen.
They will be there for the remainder of the winter. A seal can push its head through ice that is thin and young. These holes are easily accessible by bears so it is not surprising that freshly frozen narrow leads with new = breathing hole make a great hunting spot for seals. As winter progresses, and any remaining cracks freeze, seals are limited to the area surrounding the breathing holes. They maintain this by scraping the ice with their heavy claws on the foreflippers. Over time, drifting snow builds up over cracks and pressure points, covering all signs of the location of the breathing holes. Later in winter,
When the snow drifts above the breathing holes get deeper and the wind makes the snow stick to the surface, some ringed seals dig small lairs like snow caves to rest above their breathing holes. These sub nivean (below the snow) lairs are used by pregnant females to give birth to their puppies in spring.
The arctic sea-ice’s white, icy surface appears as lifeless in winter and spring as deserts. The horizon is dotted with jagged ice pressure ridges that run along its edges. Snowdrifts can be found there. There are no seals to be seen. The occasional tracks of an arctic Fox or polar bear remind you that animals exist. However, there is plenty of life if you know how to find it. However, for polar bears, looking is not as effective as sniffing. The extraordinary sense of smell of the polar bear allows it to find ringed seal breathing holes under the snow from more than a kilometer upwind. However, at first, we didn’t realize how amazing its abilities were.
The polar bear seems to be unaware of the possibility that anything is about as it plods along the ice. The bear is constantly smelling the wind while it walks. Sometimes, the bear will stop to check for any scents it may have caught and look around again.
The distance between the point of interest and the bear’s behavior when it crosses the sea ice is typically 50-100m (164-135 ft). This distance was initially thought to indicate how far a bear could sense a breathing hole beneath the snow. I was impressed considering how poor a human’s senses of smell are. My long-time friend, Tom Smith (arctic seal biologist), and Bug, his amazing dog, allowed me to participate in studies on ringed sealing birth lairs. We wanted to compare the importance of different types of ice and snow used by seals, as we were able to do so with Jimmy Memorana (who was an encyclopedia on life on the sea-ice). We thought this would allow us to understand the hunting behavior of polar bears, and how they choose their habitat. We were also asked to assess the importance of various sea ice habitats for seals to help determine how different industrial activities such as year-round shipping or offshore drilling in ice-covered water might have minimal impact. No one knew how to approach such a daunting problem quantitatively. Jimmy suggested that we use a frozen seal pup, which had been eaten by a bear but killed, to teach Bug how to spot seals like the old folks used to do. Bug, an intelligent Labrador retriever, was extremely motivated so we told Bug that the frozen seal pup was a bird and placed it in snowdrifts. Then, we sent her off to search for it. She was able to pick up almost immediately. She was soon able to utter the command “Go find those birds!” She ripped it across the sea ice and sniffed out seal lairs. We were amazed at the number of structures she discovered so quickly, and often in very small areas. Most impressive was the distances she could sense things. From a distance of at least a kilometer, Bug was able to detect a seal’s breathing hole. We were stunned.
I believe that the sense of smell that a polar bear has, which is its survival mechanism, is at least as sophisticated as that of a Labrador retriever.
We were shocked at how far the dog could see seals from. It was obvious that the bear we saw casually walking over the sea ice, occasionally testing the wind, but not showing any indication of being aware of anything, was anything other than casual. Working with Bug revealed that any bear walking on sea ice should be smelling a variety of smells. These smells could indicate breathing holes, abandoned lairs or lairs being used by seal pups. We could not see the cues used by the bears, but it was obvious that they were very selective in where they hunted.
Most still-hunting in the winter and spring is done standing, rather than lying down. A bear will choose a spot to hunt and then creep slowly and stealthily up to it. It then stands still, with its hind feet closer than its front feet. Sometimes, bears in this position may appear to be about to urinate. This oddly-shaped posture allows the bear to shift its weight onto its hind feet, without having to move them. Seals below would hear the sound through the snow. The bear will then slowly shift its weight onto its hind legs if it smells or hears a seal under the snow. It will raise its forelimbs up above its head briefly before falling to the ground with its front paws in an attempt to reach the snow beneath. Sometimes, the snow is so hardened from the winter wind, even large bears must pound down on their forepaws multiple times in rapid succession to try to break through the snow. Sometimes the bear can break through snow in one go, but it is more common to need several hits to get the snow’s hard surface out of reach. If the bear has to wait for a long time before it can break into the lair, the lair will be empty. This illustrates how crucial a subnivean roof can be for the survival of seals and pups.
While accounts of seal hunting in journals of early naturalists and explorers tend to concentrate on the bear-snapping of seals, it is evident that Inuit hunters were much more attentive. Many of the techniques they used to hunt seals seem to have been copied from polar bears. Charles Francis Hall’s journals contain vivid stories of hunters waiting patiently with spears over seal breathing holes for hours in freezing temperatures. Hunters know that seals will not be able to breathe if the lair is broken into. After clearing the snow from a breathing hole, the hunter would cover it with snow. To keep the light out, he would place a feather or small stick in the tiny hole. The hunter would know when to insert his harpoon if the feather moves because it indicated that a seal was present. The hunter used to stand on a piece polar bear fur to keep his feet warm and make less noise during long hunts. Inuk hunters may have had the idea to make a white cloth screen for themselves after watching polar bears chase seals across open ice. Although it’s impossible to know if these speculations are true, it seems plausible that Inuk hunters learned a lot from polar bears about seal hunting.
Polar bears enter seal lairs right above the breathing hole. If a bear captures a young pup with very little body fat, it may kill it but not eat it. The most amazing thing I have ever seen a hunting bear do is to head-first descend a hole after it has broken into a birth lair deep in the snow. Sometimes, the bear may continue hunting in this way for long enough to leave a clear impression of his forearms in the snow near the breathing hole. This behavior may block sunlight from reaching the breathing hole. According to Inuk hunters, this behavior may cause the mother of a ringed seal to believe that her lair is safe and intact. Sometimes, the fe male might return to check on her pup and get caught. The pups of nursing female seals are more fat than the pups, and they provide much more nutrition to a polar bear.
Learning to Hunt
For two and a quarter years, polar bear cubs stay with their mothers. They watch her hunt in many different conditions in all seasons. As with all predators, cubs learn from their mother first and then by copying her behavior. Cubs-of the-year hunt almost nothing in the first spring or summer after they leave the maternity den. They follow their mother closely, following her every move and looking curiously in the same places. They learn to recognize changes in their mother’s behavior and to immediately spot a location to rest or lie down. The cubs are instructed to immediately lie down and wait for her to finish. The cubs usually wait patiently and are well-behaved. However, some cubs get bored or just curious and start to approach the mother before she is done. It is common for two cubs to become distracted after waiting a while, and then start playing. One cub will usually initiate the play by pushing or biting its sibling. The other cub responds quickly. Soon, the two cubs are chasing each other across the ice, biting, rolling over and chasing each others. They seem to enjoy running through the shallow pools of meltwater on the ice surface in the summer. If they disrupt their mother’s hunt, such as running around or playing with each other, she might show her displeasure by giving them a few sharp cuffs. After that, the cubs will be much more cooperative… for a while anyway.
They learn to observe their mother and to look at the site she hunts. They still hunt very little at 18 months old. Their hunts are shorter than those of adult bears and they rarely catch a seal. They rarely catch a seal, but it is often a young ringed seal pup who has just learned to avoid polar bears.
It was comical to see one cub so interested in her mother’s hunting. Its mother was an expert at the aquatic stalk. She would then flatten herself in a channel of water in the ice, and then slowly push herself towards the seal. G her cub, following her closely, followed her with its head down, just a few meters behind her. She was watching every move of her cub, but she was also visible to every seal she chased. The mother did not seem to be able to notice that her cub was being shadowed.
But sometimes, single cubs can get tired of waiting. One cub that I observed was especially energetic. After a short wait, he would run long, running leaps into the melt pools of the ice. This made for some spectacular splashes. One time, as he was flying toward the water through the telescope, a seal appeared in front of him. The yearling, who was astonished, grabbed the carcass by the head and pulled it from the ice. He didn’t eat his kill right away like other bears. Instead, he raced around on the ice with it, throwing it in the air, and running after it. He then began to throw the carcass into the water, dive in and retrieve it. The yearling’s mother looked up and saw the seal. She raced to get it and began eating it right away. The seal was small and clearly only a few months old. An adult seal wouldn’t have faced the cub as energetically. Young bears learn to hunt by themselves when there is a lot of fat, but young seals.
Two-year-old yearling cubs hunt 4% and 7% respectively while their mothers hunt from 35-50%. We observed that yearlings caught one seal every 22 days while their mothers caught one every four- to five days during summer, and one every two or three days in April and may. Two-year-olds didn’t hunt as much in July. However, they did catch one seal on average every five to six hunting days in July after becoming independent and weaned. This indicates that they had learned a lot more over the year.
The way that cubs choose where to hunt is another factor that may influence the number of seals killed. Yearlings and cubs-of the-year tend to follow their mother closely and mimic her movements. These younger cubs will hunt the female when she is still hunting. They will do so more often than where they were standing before the female stopped moving. Picking a hunting spot is a decision that must be made in a group. Two-year-old cubs, however, can choose their hunting spots independently. They will still be accompanied by their mothers for a distance of 0.6 to 1.2 km. A cub can learn to hunt fairly well by the age of two-and-a-half years, but it doesn’t seem to want to practice a lot, perhaps because its mother still provides food. The cub may be lazy. Yearlings and 2-year-olds don’t hunt much in the spring. They are likely too small and light for them to break through snowdrifts fast enough to capture a seal. Polar bear cubs may stay with their mothers so long because they need more time to become large enough to hunt during winter and spring.
References & Further Reading
Canino, W. and Powell, D. 2010. Formal Behavioural Evaluation of Enrichment Programs on a Zookeeper’s Schedule: A Case Study With a Polar bear (Ursus maritimus) at the Bronx Zoo, Zoo Biology 29:503 508.
Derocher, A.E., and Wiig, O.1999. Infanticide and cannibalism of juvenile polar bears (Ursus maritimus) in Svalbard. Arctic 52:307-10.
Derocher, A.E., and Stirling 1. 1990. Aggregating behaviour of adult male polar bears (Ursus maritimus). Canadian Journal of Zoology 68:1390 1394.
Derocher A.E. et al. 2010. Nursing vocalization of a polar bear cub. Ursus 21: 189-191.
Furnell, D.J., and Oolooyuk, D. 1980. Polar bear predation on ringed seals in ice-free water. Canadian Field-Naturalist 94:88-89.
Kingsley, M.C.S., and Stirling, I. 1991. Haul-out behaviour of ringed seals in relation to defence against predation by polar bears. Canadian Journal of Zoology 69:1857-1861.
Lunn, N.J., and Stenhouse, G.B. 1985. An observation of possible cannibalism by polar bears (Ursus maritimus). Canadian Journal of Zoology 63:1516-1517.
Ramsay, M.A., and Stirling, I. 1986. On the mating system of polar bears. Canadian Journal of Zoology 64:2142-51.
Stirling, I. 1974. Midsummer observations on the behaviour of wild polar bears (Ursus maritimus). Canadian Journal of Zoology 52:1191-1198.
Stirling, I. and Latour. P.B. 1978. Comparative hunting abilities of polarClom:56:1768
Aars, J. and Plumb, A. 2010. Polar bear cubs may reduce chilling from icy water by sitting on mother’s back. Polar Biology 33:557-559
Ames, A. 1994. Object Manipulation in Captive Polar Bears Ninth International Conference on Bear Research and Management, Missoula, Montana 9:443-449.
Amstrup, S.C. et al. 2006. Intraspecific predation and cannibalism among polar bears in the Southern Beaufort Sea. Polar Biology 29: 997-1002.
The study of mtDNA nucleotide sequence shows that the brown bear ancestors separated from black bear ancestors around 1.2 – 1.5 million years ago. According to the fossil records black bears split from brown bears lineage approximately 1.5 – 2.5 million years ago.
