The World of Polar Bears

  • Introduction

    The polar bear (Ursus maritimus) is a carnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is a large bear, approximately the same size as the omnivorous Kodiak bear (Ursus arctos middendorffi). A boar (adult male) weighs around 350–700 kg (772–1,543 lb), while a sow (adult female) is about half that size. Although it is the sister species of the brown bear, it has evolved to occupy a narrower ecological niche, with many body characteristics adapted for cold temperatures, for moving across snow, ice and open water, and for hunting seals, which make up most of its diet. Although most polar bears are born on land, they spend most of their time on the sea ice. Their scientific name means “maritime bear” and derives from this fact. Polar bears hunt their preferred food of seals from the edge of sea ice, often living off fat reserves when no sea ice is present. Because of their dependence on the sea ice, polar bears are classified as marine mammals.

    Because of expected habitat loss caused by climate change, the polar bear is classified as a vulnerable species, and at least three of the nineteen polar bear subpopulations are currently in decline. However, at least two of the nineteen subpopulations are currently increasing, while another six are considered stable. For decades, large-scale hunting raised international concern for the future of the species, but populations rebounded after controls and quotas began to take effect. For thousands of years, the polar bear has been a key figure in the material, spiritual, and cultural life of circumpolar peoples, and polar bears remain important in their cultures. Historically, the polar bear has also been known as the white bear.

  • Scientific Classification

    A. Order – Carnivora

    1. The scientific order Carnivora includes bears, dogs, cats, raccoons, otters, weasels, and their relatives. All typical carnivores have well developed claws and a pair of specialized cheek teeth for cutting hard foods.

    B. Family – Ursidae

    1. All bears belong to this family. The family is divided into three subfamilies, Ursinae (black bears, brown bears, polar bears, sloth bears, and sun bears), Tremarctinae (spectacled bears), and Ailuropodinae (giant pandas).

    C. Genus, species – Ursus maritimus

    1. There are five other species in the genus Ursus: brown bears, American black bears, Asiatic black bears, sun bears, and sloth bears. Species can be distinguished by size, build, coloration, and habitat.
    2. Ursus maritimus is Latin for “sea bear”.
    Polar bear in the water

    D. Fossil record

    1. The oldest known polar bear fossil is less than 100,000 years old. Polar bears probably developed during the Pleistocene era from an ancestral brown bear. Polar bears and brown bears are still closely related; when cross-bred, they produce fertile offspring.
  • Habitat und Distribution

    A. Distribution

    1. Polar bears are found throughout the circumpolar Arctic.
    2. Polar bears, or their tracks, have been reported almost as far north as the pole; however, scientists believe few bears frequent areas north of 82 north latitude. The northern Arctic Ocean has little food for them.
    3. The polar bears’ southern range is limited by the amount of sea ice that forms in the winter. Polar bears prefer to travel on sea ice.
      a. In the south, polar bears are annual visitors to St. Lawrence Island, southern Labrador, and Svalbard.
      b. In heavy ice years, polar bears have travelled as far south as the Pribilof Islands, Kamchatka, Newfoundland, and Iceland.
      c. The most southerly dwelling polar bears live year-round in James Bay, Canada.
    4. The majority of polar bears are found near land masses around the edge of the polar basin.
    5. Scientists believe there are 15 relatively discrete polar bear subpopulations (Wiig, 1993-94). A subpopulation is a group of polar bears with a home range independent of but overlapping that of other polar bears. For example, two subpopulations live in the James/Hudson Bay area, one in western Hudson Bay and the other in north-western Ontario and James Bay (Stirling, 1988).

    B. Habitat

    1. Polar bears inhabit Arctic sea ice, water, islands, and continental coastlines.
    2. Polar bears prefer sea ice habitat with leads, next to continental coastlines or islands(Stirling, 1993).
      a. Leads are water channels or cracks through ice which may remain open (ice free) for only a few minutes to several months, depending upon weather conditions and water currents.
      b. Polar bears hunt seals in the leads, using sea ice as a platform.
      c. The “Arctic ring of life” is a biologically rich system of leads and polynyas. It runs parallel to the polar basin coastline.
      (1) Polynyas are areas of water, surrounded by ice, that remain open throughout the year due to winds, upwellings, and tidal currents.
      (2) Polynyas are important breathing and feeding areas for wintering or migrating marine mammals and birds.
    3. Some polar bears spend part of the year on land.
      a. Polar bears in warmer climates may become stranded on land. In summer, sea ice melts along the coastlines, and pack ice (floating sea ice, or floes, not connected to land) moves north.
      b. Most pregnant females spend the autumn and winter on land in maternity dens.
    4. Air temperatures in the Arctic average -34C (-29F) in winter and 0C (32F) in summer. The coldest area in winter is north-eastern Siberia, where the temperature has been recorded as low as -69C (-92F). The warmest areas in summer are inland regions of Siberia, Alaska, and Canada where temperatures can reach as high as 32C (90F).
    5. The ocean temperatures in the Arctic are about -1.5C (29F) in summer. In winter the ocean temperatures can drop to -2C (28F), at which point seawater freezes.

    C. Migration

    1. Polar bears travel throughout the year within individual home ranges.
      a. Home range size varies among individuals depending upon access to food, mates, and dens (Stirling, 1988).
      b. Home ranges tend to be larger than for other mammal species because sea ice habitat changes from season to season and year to year.
      (1) A small home range may be 50,000 to 60,000 square km (19,305/23,166 square mi.). Small home ranges can be found near Canadian Arctic islands.
      (2) A large home range may be in excess of 350,000 square km (135,135 square mi.). Large home ranges can be found in the Bering or Chukchi Seas.
      c. Polar bears don’t mark or defend their home ranges.
    2. Polar bears show “seasonal fidelity”: they remain in the same area during the same season (Stirling, 1988).
    3. Polar bears are capable of traveling 30 km (19 mi.) or more per day for several days (Stirling, 1988). One polar bear was tracked traveling 80 km (50 mi.) in 24 hours (Sage, 1986). Another polar bear travelled 1,119 km (695 mi.) in one year (Macdonald, 1987).

    D. Population

    1. The world polar bear population is estimated to be between 21,000 and 28,000 individuals (Wiig, 1993/94).
    2. Due to governmental regulations on hunting, the population has increased from an estimated 10,000 polar bears in 1968 (Stirling, 1988).
    3. The ratio of males to females is approximately one to one.
  • Physical Characteristics

    A. Size

    1. Polar bears are the largest land carnivore.
    2. Male polar bears (boars) grow two to three times the size of female polar bears (sows). Boars weigh about 350 to more than 650 kg (772-1,433 lb.) and are about 2.5 to 3 m (8.2-9.8 ft.) long (Stirling, 1988).
    3. Sows weigh about 150 to 250 kg (331-551 lb.) and are about 2 to 2.5 m (6.6-8.2 ft.) long. Pregnant females can weigh as much as 500 kg (1,102 lb.) (Stirling, 1988).
    4. The largest polar bear ever recorded was a male weighing 1,002 kg (2,209 lb.) and measuring 3.7 m (12 ft.) long (Domico, 1988).

    B. Body shape

    Compared to other bears, polar bears have elongated bodies and long slender necks.

    C. Coloration

    The coat can vary from pure white to creamy yellow to light brown depending upon season and angle of light.

    D. Limbs

    1. The hind limbs are longer than the forelimbs. This makes the large, muscular hind end stand higher than the shoulders.
    2. Polar bear legs are large and stocky.
    3. Feet are five-toed paws.
      a. Polar bears have large paws compared to body size, reaching 30 cm (12 in.) in diameter. The large paws of a polar bear act like snowshoes, spreading out the bear’s weight as it moves over ice and snow.
      b. The forepaws are round, and the hind paws are elongated.
      c. Each toe has a thick, curved, nonretractable claw. The claws are used for grasping prey and for traction when running or climbing on ice.
      d. The sole of a polar bear’s foot has thick, black pads covered with small, soft papillae (dermal bumps). The papillae create friction between the foot and ice to prevent slippage. Long hairs growing between pads and toes also help prevent slippage.

    E. Head

    1. A polar bear’s head is oblong and relatively small compared to body size. The muzzle is elongated with a “Roman-nosed” (slightly arched) snout.
    2. The nose is broad and black.
    3. Teeth.
      a. Polar bears have 42 teeth, which they use for catching food and for aggressive behaviour.
      b. Polar bears use their incisors to shear off pieces of blubber and flesh.
      c. Canine teeth grasp prey and tear tough hides.
      d. Jagged premolars and molars tear and chew.
      e. Polar bears swallow most food in large chunks rather than chewing.
    4. A polar bear’s eyes are dark brown, set relatively close together, and look forward.
    5. The ears are small and rounded and lay flat when under water.

    F.Tail

    The tail is small, about 7 to 12 cm (2.8-4.7 in.) long.

    G.Hair

    1. Polar bears are completely furred except for the nose and footpads, which are black.
    2. A polar bear’s coat is about 2.5 to 5 cm (1.2 in.) thick. A dense, woolly, insulating layer of underhair is covered by a relatively thin layer of stiff, shiny, clear guard hairs.
    3. Polar bear fur is oily and water repellent. The hairs don’t mat when wet, allowing the polar bears to easily shake free of water and any ice that may form after swimming. Ice forms when the wet fur is exposed to air temperatures at or below freezing.
    4. The hairs reflect light, giving a polar bear its white coloration. Oxidation from the sun, or staining, can make the hairs look yellow or brown.
    5. Polar bears completely molt (shed and replace their fur) annually, in May or June. The molt can last several weeks.

    H.Skin

    A polar bear’s skin is black.

  • Senses

    A. Hearing

    A polar bear’s hearing is probably as sensitive as human hearing. Humans can hear sounds with frequencies as low as 0.02 kHz and as high as 20 kHz.

    B. Eyesight

    The eyesight of polar bears appears to be similar to human’s. Polar bears have a protective membrane over their eyes, that may help shield the eyes from ultraviolet light.

    C. Tactile

    Little is known about a polar bear’s sense of touch; however, polar bears have been observed delicately moving or touching objects with the nose, tongue, and claws.

    D. Taste

    Polar bears prefer certain foods, but researchers don’t know how acute the sense of taste is or how important it is in food preference.

    E. Smell

    A polar bear’s sense of smell is acute, and it is the most important sense for detecting prey on land. A polar bear can smell a seal more than 32 km (20 mi.) away (Domico, 1988).

  • Adaptations for an Aquatic Environment

    A. Swimming

    1. Polar bears are strong swimmers; they swim across bays or wide leads without hesitation. They can swim for several hours at a time over long distances. They’ve been tracked swimming continuously for 100 km (62 mi.) (Stirling, 1988).
    2. A polar bear’s front paws propel them through the water dog-paddle style. The hind feet and legs are held flat and are used as rudders.
    3. A thick layer of blubber (fat), up to 11 cm (4.3 in.) thick, keeps the polar bear warm while swimming in cold water (Stirling, 1988).
    4. Polar bears can obtain a swimming speed of 10 kph (6.2 mph) (Stirling, 1988).
    5. The hair of a polar bear easily shakes free of water and any ice that may form after swimming.
    6. A polar bear’s nostrils close when under water.

    B. Diving

    1. Polar bears make shallow dives when stalking prey, navigating ice floes, or searching for kelp.
    2. Polar bears usually swim under water at depths of only about 3 to 4.5 m (9.8-14.8 ft.). They can remain submerged for as long as two minutes (Domico, 1988).
    3. No one knows how deep a polar bear can dive. One researcher estimates that polar bears dive no deeper than 6 m (20 ft.).

    C. Thermoregulation

    1. Body temperature, which is normally 37C (98.6F), is maintained through a thick layer of fur, a tough hide, and an insulating layer of blubber. This excellent insulation keeps a polar bear warm even when air temperatures drop to -37C (-34F) (Stirling, 1988).
    2. Overheating.
      a. Polar bears are so well insulated they tend to overheat.
      b. Polar bears move slowly and rest often to avoid overheating.
      c. Excess heat is released from the body through areas where fur is absent or blood vessels are close to the skin. These areas include the muzzle, nose, ears, footpads, inner thighs, and shoulders.
      d. Polar bears will also swim to cool down on warm days or after physical activity.
  • Behavior

    A. Daily activity cycle

    1. Polar bears are most active the first third of the day and least active the final third of the day.
    2. In the Canadian Arctic, adult female polar bears with cubs hunt about 19% of their time during the spring and about 38% of their time during the summer. Adult male polar bears hunt about 25% of their time during the spring and about 40% of their time during the summer (Stirling, 1978).
    3. When not hunting, polar bears are often sleeping or resting.
      a. On warm days polar bears sprawl out on the ground or ice, sometimes on their backs with their feet in the air. They may also make temporary snow or earthen pits to lie in.
      b. On cold days polar bears curl up and often cover their muzzle area. During the winter, some polar bears excavate temporary dens or find natural shelters to stay warm. They may use these shelters for several months at a time.

    B. Walking and running

    1. Like humans, polar bears walk on the soles of their feet with their heels touching the ground first. Like other bears, they can also stand on their hind feet and walk upright for short distances.
    2. Polar bears generally walk with a steady, lumbering gait. The front paws swing outward with each step, landing slightly pigeon-toed. The head swings gently from side to side. The walk has a four-beat pattern, first the right front foot touches the ground, then the left hind foot, then the left front foot, and lastly, the right hind foot.
    3. The bulky build and swinging gait cause polar bears to use more than twice as much energy to move at a given speed than most other mammals (Stirling, 1988).
    4. The average walking speed of a polar bear is 5.5 kph (3.4 mph) (Stirling, 1988).
    5. When being chased or charging prey, polar bears can run as fast as 40 kph (25 mph) for short distances (Domico, 1988).

    C. Social structure

    1. Polar bears are basically solitary. Usually, only two social units exist: (1) adult females with cubs and (2) breeding pairs.
    2. Polar bear aggregations.
      a. Polar bears will aggregate to feed on large whale carcasses and at dump sites.
      b. In some southern regions, like Hudson Bay, bears aggregate on land during the ice-free summer and autumn months.
    3. On occasion, adult and sub adult (ages 30 months to five or six years) polar bear males will feed and travel together for short periods of time.

    D. Social behaviour

    1. The most constant social interaction occurs between mother and cubs. Polar bear mothers are attentive, frequently touching and grooming their cubs.
    2. Polar bear breeding pairs remain together for one week or more, mating several times.
    3. Aggression occurs between males during the breeding season and when males attempt to steal food caught by other polar bears.
    4. Play fighting has been observed between aggregating sub adult and adult male polar bears.
    5. Young polar bear cubs chase and tackle their siblings.

    E. Hibernation

    1. Hibernating means to pass the winter in a dormant or lethargic state. Animals that hibernate store body fat when food is plentiful. When food is scarce, they hibernate, living off their stored body fat.
    2. Polar bears don’t enter deep hibernation. Deep hibernation applies to an animal whose body temperature drops to 5C (41F) for a period of days or weeks. Deep hibernators also show a marked drop in heart rate, and are slow to wake up when disturbed.
    3. Only pregnant female polar bears hibernate.
      a. Polar bears aren’t deep hibernators, but enter a state of carnivore lethargy. Though hibernating females sleep soundly, they’re easily and quickly aroused.
      b. The female polar bear’s heart rate slows to about 27 beats per minute from a normal resting heart rate of about 46 beats per minute (Stirling, 1988).
      c. When hibernating, a female’s body temperature may drop slightly, perhaps to 35C (95F), or it may remain normal at 37C (98.6F). Unlike most other hibernators, female polar bears give birth while hibernating. High body temperature is needed to meet the demands of pregnancy, birth, and nursing (Stirling, 1988).
    4. Researchers have found that nonhibernating polar bears, during times of food scarcity, can efficiently utilize their energy reserves much like hibernating bears (Stirling, 1988).

    F. Tracking

    1. Scientists use radio collars to track the movements of polar bears.
      a. Once a polar bear is fitted with a radio collar, the collar sends signals to a receiving station via satellite. Scientists can enter the data into a computer program that plots the polar bear’s path.
      b. Only female polar bears can be tracked using radio collars. Male polar bears have necks wider than their heads, and the collars simply fall off.
    2. The movements of polar bears can also be studied by following their tracks in the snow, usually by aircraft.
    3. Other behaviours are recorded by observing polar bears directly, or finding evidence of polar bears, such as a partially eaten seal.
    4. Most polar bear research is conducted in the spring or summer when weather conditions are more favourable to humans.

    G. Attacks on humans

    1. Humans may encounter polar bears wherever human and polar bear habitats overlap. Polar bear attacks occur most often at sites of human habitation, such as hunting camps, weather stations, and towns. Compared to other bears, polar bears are more willing to consider humans as prey. Consequently, the person attacked is usually killed unless the polar bear is killed first.
    2. Polar bear subadults and females with cubs attack most often. They’re also the chief scavengers (among polar bears) of human dump sites. Both groups tend to be thinner and hungrier; subadults are inexperienced hunters, and females with cubs must feed themselves and their young.
  • Diet and Eating Habits

    A. Food preferences and resources

    1. Polar bears feed mainly on ringed seals and bearded seals. Depending upon their location, they also eat harp and hooded seals and scavenge on carcasses of beluga whales, walruses, narwhals, and bowhead whales.
    2. On occasion, polar bears kill young walruses and beluga whales.
    3. When other food is unavailable, polar bears eat reindeer, small rodents, seabirds, ducks, fish, eggs, vegetation (including kelp), berries, and human garbage.

    B. Food intake

    1. A polar bear’s stomach can hold an estimated 15% to 20% of its body weight. It can assimilate 84% of the protein and 97% of the fat it eats (Stirling, 1988).
    2. Polar bears need an average of 2 kg (4.4 lb.) of fat per day to survive. A ringed seal weighing 55 kg (121 lb.) could provide up to eight days of energy for a polar bear (Stirling, 1988).

    C. Methods of collecting and eating food

    1. Still hunting.
      a. Still hunting is the most common method of hunting year-round.
      b. The polar bear remains motionless beside a breathing hole or lead edge waiting for a seal to surface. When a seal surfaces, the polar bear bites onto the head or upper body, then flips the entire seal onto the ice.
      c. Still hunting usually takes less than one hour, but polar bears will wait much longer.
    2. Stalking on land.
      a. Stalking is a hunting method used in summer when seals haul out on sea ice.
      b. Once spotted, the seal is slowly and steadily stalked by the polar bear. At 15 to 30 m (49.98 ft.) away, the polar bear suddenly charges the seal. With its claws or teeth, the polar bear grabs the seal before the seal can leave the ice.
    3. Aquatic stalk.
      a. The aquatic stalk is a method also used in summer when seals haul out on sea ice.
      b. The polar bear swims toward a hauled-out seal. Once the polar bear reaches the ice edge, the bear quickly emerges from the water and grabs the seal with its claws or teeth.
    4. Stalking birth lairs.
      a. Stalking ringed seals at their birth lairs is a hunting method polar bears use in spring, when ringed seals give birth to their pups.
      b. Ringed seal birth lairs are caves built under snow drifts next to a hole in the ice. The snow drifts are on stable sea ice attached to land.
      c. Once a polar bear identifies a birth lair, it slowly and quietly positions itself next to the lair. If a polar bear smells or hears a seal in the lair, it slowly raises up on its hind legs and crashes down with its front paws to break through the lair roof.
      d. To break the roof’s hard surface, several tries are sometimes needed, which may allow the seal to escape into the water.
      e. This method is most commonly used by polar bear females with cubs under one year old.
      (1) Mother seals and pups have the high fat content needed for hungry polar bear mothers and their growing cubs.
      (2) Male polar bears that may attack young polar bear cubs don’t normally hunt seals in birth lairs.
      (3) Birth lairs are usually on sea ice attached to land, allowing young cubs (who have little protective blubber) to avoid crossing water.
    5. Eating.
      a. Once a seal is captured, a polar bear bites it several times on the head and neck before dragging it several meters from the water to feed.
      b. The skin and fat are eaten first, followed by the meat.
      c. Polar bears often stop to wash during feeding, using water nearby or rubbing in the snow.
      d. Polar bears don’t always eat the entire kill. Carcass remains are scavenged by other bears, arctic foxes, and gulls.
  • Reproduction

    A. Sexual maturity

    1. Female polar bears reach sexual maturity at about 4 years (Stirling, 1988).
    2. Male polar bears reach sexual maturity at about 6 years (Stirling, 1988).
    3. Most male polar bears don’t successfully mate until 8 to 10 years and older.

    B. Mating activity

    1. Breeding takes place in April and May on the sea ice.
    2. During the breeding season, males and females find each other by congregating in the best seal-hunting habitats.
    3. Male polar bears have been seen following the tracks of breeding female polar bears for more than 100 km (62 mi.). Scientists are uncertain what signals males use to track breeding females.
    4. Competition for females is intense. Females breed about once every three years; therefore, there are about three adult males to every breeding female.
    5. Before mating, a female polar bear may be accompanied by several males. The males fight fiercely among themselves until the strongest or largest male succeeds in chasing the others away.
      a. A polar bear threatening to attack another polar bear usually lowers its head, flattens its ears back, and gives an open mouth threat with a hisslike roar.
      b. Fights are rarely fatal, but do result in broken canines and scars on the head, neck, and shoulders.
    6. Dominant males may succeed in breeding several females in a season.
    7. Once paired, the male and female stay together for a week or more.
      a. Females are induced ovulators, which means the act of mating causes a female to release an egg for fertilization.
      b. Several days of mating interactions may be required to stimulate ovulation and guarantee fertilization of the egg.
    8. Polar bears may have many different mates over their lifetime.
  • Birth and Care of Young

    A. Gestation

    1. The total gestation period is about eight months.
    2. Gestation includes a period of delayed implantation.
      a. The fertilized egg divides into a hollow ball of cells one layer thick (a blastocyst), then stops growing and lies free-floating in the uterus for about four months. The blastula then implants in the uterine wall and continues to develop.
      b. Delayed implantation assures that the cub is born during the best time of the year for survival and allows the female to get into good physical condition and use her energy for nursing her new-born cubs.
      c. The actual embryonic development is estimated to be four months.

    B. Denning

    1. Once mated, females begin depositing fat in preparation for cubbing. Females need to gain at least 200 kg (441 lb.) for a successful pregnancy (Stirling, 1988).
    2. Some females may seek out maternity dens as early as late August, but most enter dens in mid to late October. Dens protect new-born cubs from winter’s temperature extremes.
    3. Females usually dig dens in snowdrifts on southerly facing slopes. Some dig earthen dens that later become covered by snow.
    4. Most dens are on land, within 16 km (10 mi.) of the coast. In some areas, dens are more than 100 km (62 mi.) from the coast. A few polar bears make dens on the sea ice (Harington, 1968).
    5. Den elevations range from sea ice level to 548.6 m (1,800 ft.) above sea level (Harington, 1968).
    6. Most dens consist of a single chamber slightly elevated from a short entrance tunnel. On average, the chamber is 2 m (6.6 ft.) long, 1.5 m (4.9 ft.) wide, and 1 m (3.3 ft.) high. Polar bears maintain a ventilation hole through the chamber ceiling to provide fresh air (Stirling, 1988).
    7. Because of body heat and snow insulation, the den stays warmer than the outside air temperature.

    C. Birth seasons

    Polar bear cubs are born November through January in a den. Mother and cubs emerge from their den in late March or April.

    D. Frequency of birth.

    1. Most adult females give birth once every three years. In some populations, birth occurs once every two years.
    2. The most frequent litter size is two, followed by litters of one. Litters of three are less common than twins or singles, and litters of four are rare.

    E. Cubs at birth

    1. At birth, polar bear cubs weigh about 454 to 680 g (16-24 oz.) and are about 30 cm (12 in.) long. Males are born slightly larger than females.
    2. Polar bear cubs are born small and helpless, with their eyes closed.
    3. The fur is very fine at birth, making the cubs look hairless.

    F. Care of young

    1. Nursing.
      a. Female polar bears have four mammary glands. Mothers nurse their cubs in a sitting position, or lying down on their side or back.
      b. During their first few weeks of life, polar bear cubs nurse most of the time and stay close to their mother to keep warm.
      c. For the next three or four months the cubs nurse as often as six times a day. The length and number of nursings gradually decreases as the cubs grow older.
      d. Mother polar bears nurse their cubs for as long as 30 months. Some cubs stop nursing as young as 18 months of age, but remain with their mothers for survival until they are 30 months old.
      e. The average fat content of polar bear milk is 33%, similar to the milkfat of other marine mammals (Stirling, 1988).
    2. Mother polar bears are extremely protective of their young, even risking their own lives in their cubs’ defence.

    G. Cub growth and development

    1. Cubs open their eyes within the first month.
    2. The cubs begin walking while in the den at about two months. By this time, they also have thick, whitish fur and their teeth have erupted.
    3. By the time the mother and cubs emerge from the den in late March or April, the cubs weigh 10 to 15 kg (22-33 lb.).
    4. Mother and cubs remain around the den for about 12 more days, sometimes longer.
      a. This enables the cubs to acclimate to the colder weather and develop their walking muscles.
      b. During this time the cubs still spend about 85% of their time in the den, sleeping there at night.
    5. When ready, the mother polar bear leads her cubs to sea ice. Travel is slow with frequent rest and nursing stops. A mother will sometimes carry her cubs on her back through areas of deep snow or water.
    6. Cubs begin eating solid food as soon as their mother makes her first kill on the sea ice (about three to four months of age).
    7. The cubs grow quickly on their mother’s fat rich milk and on seal blubber. By eight months of age, they weigh over 45 kg (99 lb.).
    8. Polar bear cubs learn to hunt by watching their mother. Cubs will try hunting in their first year, but don’t seem to be successful until they’re over one year old. Even then, they only spend about 4% of their time hunting. By the time they’re two years old they spend about 7% of their time hunting and can catch a seal every five or six days (Stirling, 1978).
    9. When her cubs are about 30 months old, a female polar bear is ready to breed again. At this time, an adult male may begin following her. Either the mother bear or the male chases away the cubs.
  • Communication

    A. Vocalizations

    1. Adult polar bears vocalize most when they’re agitated or threatened. Sounds include hissing, growling, champing of teeth, and soft chuffing.
    2. Cubs vocalize more often and for diverse reasons. Sounds include hissing, squalling, whimpering, lip smacking, and throaty rumblings.
    3. Mothers warn cubs with a chuffing or braying sound.

    B. Other communication

    1. Polar bears also communicate through sight, touch, and smell.
    2. A male polar bear initiates play fighting by approaching another male with its head down, mouth closed, and eyes averted. The bears usually make contact by gently touching or “mouthing” each other around the face and neck. They then proceed to rear up on their hind legs and try to push each other over with their forepaws.
    3. A mother polar bear can comfort, protect, or punish her cubs by using her body, muzzle, or paws.
  • Longevity and Cases of Death

    A. Longevity

    1. Polar bears can live 20 to 30 years, but only a small proportion of polar bears live past 15 to 18 years (Stirling, 1988).
    2. The oldest known polar bear in the Arctic lived 32 years. The oldest known polar bear in a zoological park lived 41 years (Stirling, 1988).

    B. Aging studies

    Each year as a polar bear grows, a thin layer of cementum is added to the outside of each tooth. Age can be estimated by examining a thin slice of tooth and counting the layers. To estimate the age of a live polar bear, researchers can extract one small, vestigial premolar tooth.

    1. Adult polar bears have no natural predators. Males occasionally kill other males competing for mates. Males periodically kill females protecting cubs.
    2. Cubs less than one year old sometimes are prey to adult male polar bears and other carnivores, such as wolves.
    3. New-born cubs may be cannibalized by malnourished mothers.

    D. Human interaction

    1. 1.Hunting.
      a. Polar bears have been hunted for thousands of years.
      (1) Evidence of human polar bear hunts have been found in 2,500- to 3,000-year-old ruins. Arctic peoples have traditionally hunted polar bears for food, clothing, bedding, and religious purposes.
      (2) Commercial hunting of polar bears for hides began as early as the 1500s and flourished by the 1700s.
      (3) Kills increased substantially in the 1950s and 1960s when hunters began using snowmobiles, boats, and airplanes to hunt polar bears. Public concern about these hunting methods led to an international agreement in 1973 banning the use of aircraft or large motorized boats for polar bear hunts.
      b. Hunting is the greatest single cause of polar bear mortality.
      (1) Today, polar bears are hunted by native Arctic populations primarily for food, clothing, handicrafts, and sale of skins. Polar bears are also killed in defence of people or property.
      (2) Hunting is government-regulated in Canada, Greenland, and the United States. Hunting is currently banned in Norway and Russia.
    2. 2. Environmental threats.
      a. Oil spills from drilling platforms or tankers potentially threaten polar bears.
      (1) A polar bear’s fur loses its insulating properties when covered with oil.
      (2) Oil spills could diminish or contaminate polar bear food sources.
      b. The presence of toxic chemicals in polar bears may have long-term effects on their health and longevity.
      (1) Toxic chemicals from worldwide industrial activities are carried to the Arctic by air, rivers, and oceans.
      (2) Arctic animals in higher food chain levels concentrate greater amounts of toxic chemicals in their tissues than those below them. Polar bears, at the top of the food chain, develop the highest concentrations of all.
      (3) Human-made toxic chemicals such as polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), and chlordanes are present in the Arctic. These chemicals have been found in significantly high levels in the tissues of polar bears.
      (4) Scientists continue to monitor the levels of toxic chemicals in polar bears to determine their long-term effects.
      c. Radionuclides, from nuclear waste dumping in the Russian Arctic, may have detrimental effects on polar bears, and the Arctic ecosystem as a whole.

    E. Starvation

    1. Starvation is the greatest threat to subadult polar bears. Subadults are inexperienced hunters, and often are chased from kills by larger adults.
    2. Older, weaker bears also are susceptible to starvation.

    F. Disease and parasitism

    As in any animal population, a variety of diseases and parasites can be responsible for polar bear illnesses. Polar bears are especially susceptible to the parasitic worm Trichinella, which they contract by feeding on infected seals. Trichinella larvae encyst in various parts of the polar bear’s body, usually muscle tissue. If enough larvae encyst in one area, such as the heart, the tissue becomes severely damaged. Death may result.

  • Conservation

    A. First International Scientific Meeting on the Polar Bear, 1965

    Growing public concern about polar bear hunting and other human activities in the Arctic, such as oil exploration, led to the First International Scientific Meeting on the Polar Bear in 1965. Attending were representatives from all five polar bear countries: Canada, Greenland (territory of Denmark), Norway, the United States, and the former Union of Soviet Socialist Republics. The meeting set the stage for additional international conferences and research efforts, which eventually led to an international agreement on polar bear conservation.

    B. The International Agreement on Conservation of Polar Bears and Their Habitat, 1973

    1. This agreement states that the five polar bear nations (Canada, Greenland, Norway, the United States, and the former Union of Soviet Socialist Republics) shall protect polar bear habitat, especially denning areas, feeding areas, and migratory routes; ban hunting of bears from aircraft and large motorized boats; conduct and coordinate management and research efforts; and exchange research results and data.
    2. The agreement allows the taking of polar bears for scientific purposes, for preventing serious disturbances in the management of other resources, for use by local people using traditional methods and exercising traditional rights, and for protection of life and property.
    3. Each nation has voluntarily established its own regulations and conservation practices using the knowledge gained from the international community as a whole.

    C. United States Marine Mammal Protection Act, 1972

    1. Polar bears are protected under the U.S. Marine Mammal Protection Act (MMPA).
    2. The primary objective of the MMPA is to maintain the health and stability of the marine ecosystem and to obtain and maintain an optimum sustainable population of marine mammals.
    3. The MMPA prohibits taking and importing marine mammals unless a permit is issued for the purposes of public display, native subsistence, scientific research, or sustaining a depleted species. MMPA revisions in 1994 allow U.S. citizens to import polar bear “trophies” acquired in Canadian hunts. Polar bears in Alaska can be hunted only by Alaskan natives.

    D. Convention on International Trade in Endangered Species of Wild Fauna and Flora

    In 1975, the polar bear was placed on Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Appendix II includes species identified as threatened, or likely to become endangered if trade isn’t regulated. International trade of polar bears, or their parts, is permitted with proper documentation issued by the government of the exporting country.

    E. International Union for the Conservation of Nature and Natural Resources/World Conservation Union

    1. The IUCN/World Conservation Union is a worldwide conservation organization. This organization links together government agencies, non-government agencies, and independent states to encourage a worldwide approach to conservation.
    2. The Polar Bear Specialist group works under the guidance of the IUCN/World Conservation Union’s Species Survival Commission. This group helps to coordinate and identify the management and research efforts of the five polar bear nations (Canada, Greenland, Norway, the United States, and Russia).
    3. The IUCN/World Conservation Union categorizes animal species they feel are threatened. The polar bear is listed as vulnerable by the IUCN/World Conservation Union. This means the species is likely to move into the endangered category if the negative factors affecting the population continue at their present rate.

    F. Zoological parks

    1. Having polar bears at zoological parks provides the opportunity for the public to learn about these animals and how human activities may impact their survival.
    2. In the protected environment of a zoological park, scientists can examine aspects of polar bear biology that are difficult to study in the wild. Areas of study include polar bear reproduction, birth and care of young, physiology, and communication.
  • References and Bibliography / Books

    References and Bibliography

    • Derocher, A.E. and I. Stirling. “Observations of aggregating behaviour in adult male polar bears (Ursus maritimus).” Canadian Journal of Zoology 68, 1990, pp. 1390-1394
    • Dalziel, Ian W.D. “Arctic.” The World Book Encyclopedia. Chicago: World Book, Inc., 1994
    • Domico, Terry. Bears of the World. New York: Facts On File, 1988
    • Harington, Richard C. Denning Habits of the Polar Bear (Ursus maritimus Phipps). Ottawa: Canadian Wildlife Service Report Series Number 5, 1968
    • Lyman, C. P., et al. “Hibernation and Torpor in Mammals and Birds.” New York: Academic Press, 1982
    • Macdonald, David W., ed. “Encyclopedia of Mammals”. New York: Facts on File Publications, Inc., 1987
    • Nowak, Ronald M., ed. Walker’s Mammals of the World. 5th edition. Volume 2. Baltimore: The Johns Hopkins University Press, 1991
    • Parker, Sybil P., ed. Grzimek’s Encyclopedia of Mammals. Volume 3. New York: McGraw Hill Publishing Company, 1990
    • Sage, Bryan. The Arctic and its Wildlife. New York: Facts On File Publications, Inc., 1986
    • Stirling, Ian, and P.B. Latour. “Comparative hunting abilities of polar bear cubs of different ages.” Canadian Journal of Zoology 56, 1978, pp. 1768-1772
    • Stirling, Ian. Polar Bears. Ann Arbor: The University of Michigan Press, 1988
    • Stirling Ian, et al. “Habitat preferences of polar bears in the western Canadian Arctic in late winter and spring.” Polar Record 29 (168), 1993, pp. 13-24
    • Thurman, Harold V. “Arctic Ocean.”he World Book Encyclopedia. Chicago: World Book, Inc., 1994
    • Wiig, Oystein. “Polar Bear Specialist Group.” Species 21-22, December 1993-June 1994, pp. 83-84

    Books for Young Readers

    • Biel, Timothy Levi. Zoobooks 2. Polar Bears. Wildlife Education, Ltd., 1985
    • DeBeer, Hans. Little Polar Bear. New York: North-South Books, 1987 (fiction)
    • Helgeland, Glenn, ed. Arctic Animals. Chicago: Encyclopaedia Britannica, Inc., 1979
    • Larson, Thor and Sybille Kalas. The Polar Bear Family Book. Saxonville, Massachusetts: Picture Book Studio, 1990
    • Matthews, Downs. Polar Bear Cubs. New York: Simon and Schuster Inc., 1989
    • Pfeffer, Pierre. Bears, Big and Little. Ossinging, New York: Young Discovery Library, Malboro Books, 1989
    • Rosenthal, Mark. Bears. Chicago: Childrens Press, 1983
    • Stirling, Ian. Bears. San Francisco: Sierra Club Books for Children, 1992
  • Index

    Attack on humans

    Behavior
    Birth
    Body temperature
    Blubber, polar bear
    Breeding

    Carnivore lethargy
    Classification, scientific
    Claws
    Coloration
    Communication
    Conservation
    Cub

    Delayed implantation
    Den
    Diet
    Diesease
    Distribution
    Diving

    Ears
    Eyes

    Feet
    Food and feeding
    Fossil record
    Fur

    Habitat
    Hair
    Head
    Hearing
    Heart rate
    Hibernation
    Home range
    Human interaction

    Lead
    Longevity

    Marine Mammal Protection Act
    Migration
    Molting

    Nostrils
    Nursing

    Parasites
    Population
    Predators

    Skin
    Size
    Smell
    Social structure
    Starvation
    Swimming

    Tactile
    Teeth
    Thermoregulation
    Tracks

    Vocalizations

    Zoological parks

  • Links

    Polar Bears – by Encyclopædia Britannica

    Polar Bears – by WWF

    Polar Bears – by WikiPedia

    Polar Bears – ICUN (International Union for Conservation of Nature) Red List Entry

    Polar Bears – by Polar Bear Facts

    Polar Bears – by U.S. Department of the Interior/U.S. Fish and Wildlife Service

 

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