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Living Organisms / Animalia / Craniata / Mammalia / Carnivora / Ursidae / Ursus / Species

Ursus maritimus - Polar bear (Click photographs/illustrations for full picture & further details)

INDEX - INFORMATION AVAILABLE

Alternative Names (Synonyms)

• [Genus] eogroenlandicus, [Genus] groenlandicus, [Genus] jenaensis, [Genus] labradorensis, [Genus] marinus, [Genus] polaris, [Genus] spitzbergensis, [Genus] ungavensis. (B141)

Names for new-borns / juveniles

• Cub
• Cub-of-the-year (COY)
• Yearling (12 months to two years)

Names for males

Names for females

General Appearance

"Bears have a big head; a large, heavily build body; short, powerful limbs; a short tail; and small eyes. The ears are small, rounded, and erect." (B147)

• Bears are strongly built, with a broad, longish head bearing short round ears and relatively small eyes. The lips are protrusible; the molars are broad and nearly flat. They have a heavy body and a very short tail. They are plantigrade, with five toes, approximately equal in length, to each paw; the paws are wider than those of canids, and the curved, non-retractile claws are longer and stronger. (B144, B288, B424)
• Ursus maritimus - Polar bear has an elongated body, a relatively small head and long neck (compared to other bears), white fur, and the combined length of the first and second molars is less than the width of the palate. The large feet have membranes up half the length of the toes. The soles of the feet are hairy. The fur is shiny and yellowish-white. (D244, B144, B147, B180.w4, B285.w4, B288.w11, D244)

Newborn:

• Polar bear cubs are altricial; short fine white fur is present but newborn cubs are blind (closed eyes). (B147, B285.w4, B288.w11, D244)

Similar Species

• Distinguished from Ursus arctos - Brown bear by the white, not brown, coat, the combined length of the first and second molars being less, not more, than the width of the palate between the first and second molars, the small, inconspicuous ears and the head shape being "Roman nosed" rather than dished. A small muscular hump may be seen on the shoulders, but is much less prominent than in Ursus arctos - Brown bear. (B421.w1, B288.w11, D244, B490.27.w27, V.w100)

Sexual Dimorphism

• Males are larger than females in all the bears, on average their body length is about 20% greater than in females. (B147, B422.w14)
• Males have a mass about 2.1 times that of females. (J332.86.w1)
• In polar bears, for cubs newly emerged from the den, sexual dimorphism is detectable in head measurements, but not in body length or mass. The size difference is marked in bears one year old. Adult males are 2.1 times the mass of females. The size difference in adults results both from a higher growth rate in males and a longer period of growth in males, with males reaching 97% of their asymptotic body length by five years of age and 97% of asymptotic weight by 7.3 years, while males reach 97% of asymptotic length at 7.2 years and 97% of asymptotic weight by 13.5 years. Males also have longer guard hairs on the foreleg than do females. (J46.256.w1, J332.86.w1)

References

Species Authors & Referees

• See DIRECTORY- Organisations working with Bears

• Bears Status Survey and Conservation Action Plan
• See also: The Electronic Library- further reading for "Bears- Health and Management"

Husbandry Information

Notes

• Bears are large, strong mammals, adapted to climbing trees and/or difficult terrain, and with claws adapted for climbing and/or digging. Their ability to climb and to claw open trees should be remembered in designing enclosures. 
• Bears are intelligent, curious and adaptable. They are predominantly diurnal, as seen in undisturbed habitats in the wild, and are mainly solitary. 
• The behavioural, social and psychological requirements of bears must be taken into consideration in enclosure design and husbandry.

Management Techniques

• Accommodation Design for Mammals
• Mammal Behavioural Requirements
• Food and Feeding for Mammals
• Mammal Handling & Movement
• Mammal Identification
• Preventative Medicine for Mammals
• Rearing of Mammals
  • Hand-rearing Polar Bears
• Reproductive Management of Mammals
• Management of Unwanted or Illegally Held Animals

Measurement & Weight

EDITORIAL SUMMARY

LENGTH
Adult: Males reach about 2.0 - 2.6 m (79 - 102 inches) nose tip to tail tip; females are slightly shorter at 1.8 - 2.0 m (71 - 79 inches). 
Newborns: Cubs have been measured as 24 - 30.5 cm (9.5 - 12 inches) nose to tail base, and one was 34 cm (13.4 inches) nose to tail.

HEIGHT
Adults and sub-adults: Adult polar bears may measure 1.3 - 1.6 m at the shoulder (51 - 63 inches).
Juveniles: --

WEIGHT
Adult: Polar bears show a cline in size, with the smallest bears at Spitzbergen and the largest found in the Bering Strait. Weight of males varies from 300 - 730 kg (660 - 1,610 lb), but they can reach 1,000 kg (2,200 lb). Females weigh 150 - 400 kg or more (330 - 880 lb), exceptionally to 500 kg (1,100 lb) or over.
Newborns: Newborn cubs weigh about 0.6 kg (1.3 lb) at birth.

GROWTH RATE: Cubs may reach 3.5 kg at one month, 5.5 kg by two months and 11 kg by three months (based on zoo data). When they leave the maternity den in March or April, wild cubs weigh 10 - 15 kg (22 - 33 lb). At one year old, yearlings weight 90 - 160 kg (98 - 353 lb) and at two years old, 170 - 200 kg (375 - 441 lb). Females reach adult weight by about five years, males not until eight to twelve years of age.

(References are available in detailed literature reports below)

Head and Neck

EDITORIAL SUMMARY

GENERAL HEAD STRUCTURE:
Adult: Polar bears have a long neck and a relatively small head with a smooth facial profile and small ears. As with other bears, the vibrissae are vestigial. The skull is massive and the tympanic bullae are not inflated.
Newborn: The ears of newborn cubs are hairless and closed, lying pointing towards the back of the head.

DENTITION: 
Adult: Polar bears have the dental formula i3/3, c1/1, p2-4/2-4, m2/3, total 34 - 42. The canine teeth are massive and conical, reaching up to 5 cm (2 inches) long (outside the gum) while the molariform teeth have cusps elevated further than those of other bears.
Newborn: --

EYES:
Adult: The eyes are small and black; the polar bear can pull its well-developed nictitating membrane across the eye.
Newborn: The eyes are closed at birth.

(References are available in detailed literature reports below)

Legs, Spine and Tracks

EDITORIAL SUMMARY

• Polar bears have large legs and large, oar-like feet, each with five toes and large, curved, non-retractable claws 5 - 7 cm long (2.0 - 2.9 inches). 
• The soles are covered in hair around the foot pads, which both reduces heat loss through the feet and increases traction on ice. 
• The hind foot print is 305 - 330 mm (12-13 inches) long and usually 230 mm (nine inches) wide or more; the forepaw may exceed 24 cm (9.5 inches) wide in a large male.

(References are available in detailed literature reports below)

Tail

EDITORIAL SUMMARY

• Polar bears have a short tail, only about 76 - 130 mm long.

(References are available in detailed literature reports below)

Skin / Coat / Pelage

EDITORIAL SUMMARY

Adult: Adult polar bears are basically white. The dense woolly underwool traps a layer of water when the bear swims, reducing heat loss. The skin is black. The bear moults once yearly, gradually, between May and August.

Adult Colour variations: The fur may look pale to dark yellow, depending on the season, how dirty the bear is, its age and physical condition, and the light conditions. Grey or brown colouration may be seen due to dirt or sand/soil from summer earth pits. In zoos, green coats have been noted sometimes in summer, which is due to algae growing inside the shafts of the guard hairs. 

Newborn/Juvenile: Cubs have fine white hair. Some longer light brown guard hairs may be present soon after they leave the den.

(References are available in detailed literature reports below)

Detailed Anatomy Notes
(Summary information provided for pertinent species-specific data cross-referenced in Wildpro)

EDITORIAL SUMMARY

• Bears do not have any major anatomical specialisations. The large size of polar bears reduces loss of body heat.

Further information is available within this section on the musculo-skeletal system, male and female reproductive organs, gastrointestinal system, urinary system, hepatic system and adipose tissue. 

(References are available in detailed literature reports below)

Natural Diet

EDITORIAL SUMMARY

NATURAL DIET:

• The main food is the ringed seal Phoca hispida (Phoca - (Genus)); the bearded seal Erignathus barbatus (Phocidae - Seals (Family)) is also important. 
• Other seals eaten include Pagophilus groenlandicus - Harp seal and Cystophora cristata - Hooded seal (Phocidae - Seals (Family)). Walrus (Odobenus rosmarus) (Odobenidae - Walrus (Family)) and occasionally beluga Delphinapterus leucas (Monodontidae - Narwhal, white whale (Family)) are also eaten. Whales are eaten when carcasses are found. 
• When other food is unavailable, small mammals, birds, eggs, marine invertebrates and vegetation such as grasses, sedges, marine algae, seaweed, mosses, broad-leafed herbs and berries are eaten.
• Further information on feeding is provided in Polar bear Ursus maritimus - Feeding Behaviour (Literature Reports)

QUANTITY EATEN: About 4.4 kg (9.7 lb) of seal may be eaten daily (on average) over the eight months of the winter period, in Hudson Bay. Data from captive bears indicates that given a choice, polar bears will take about 80% of their diet as blubber, 20% as meat.

STUDY METHODS:

• Polar bear diets have been determined by observation of bears, tracks and carcasses.

(References are available in detailed literature reports below)

Hibernation / Aestivation

• Pregnant female polar bears den and hibernate for a period of four to eight months, from mid-October or early November to between February (in the south) to as late as May in the north. During this time they do not eat, drink, urinate or defecate, but they give birth to and suckle their cubs.
• Other polar bears may spend seven weeks to nearly three months in a den in autumn, possibly to avoid heat-stress during the ice-free period, and/or in winter to avoid inclement weather or to reduce energy expenditure when food availability is reduced.
• Polar bears appear to be able to enter a hibernation-like physiological state any time of the year if food is unavailable.

(References are available in detailed literature reports below)

Haematology / Biochemistry

HAEMATOLOGY:

• The haematology values of bears are similar to those of domestic dogs. 
• Also see Reference Page:
  •   Normal Haematology Values for Ursus maritimus - Polar bear 

BIOCHEMISTRY:

• The biochemistry values of bears are similar to those of domestic dogs. 
• Also see Reference Page
  •  Normal Biochemistry Values for Ursus maritimus - Polar bear

(References are available in detailed literature reports below)

Detailed Physiology Notes
(Summary information provided for pertinent species-specific data cross-referenced in Wildpro)

EDITORIAL SUMMARY

METABOLISM (TEMPERATURE): The normal rectal temperature of adult polar bears may vary from about 36.5 - 38.8 °C (97.7 - 101.8 °F). Polar bears use behavioural and physiological mechanisms to regulate body temperature. Polar bears use both their coat and subcutaneous fat for insulation. Excess heat is lost by conduction through the foot pads and the shoulders, and by evaporative cooling through panting.

RESPIRATORY SYSTEM (RESPIRATION): The normal respiratory rate of bears is 15 - 30 breaths per minute (the higher rates have been recorded in hot weather). Rates as low as five breaths per minute have been recorded for a sleeping bear, while panting involves 105-133 open-mouth breaths per minute.

CIRCULATORY SYSTEM (PULSE/HEART RATE): The normal heart rate of bears is 53 - 90 beats per minute (the higher rates are found in cubs) and up to 130 bpm in an active bear. 

GASTROINTESTINAL SYSTEM (FAECES AND GUT MOTILITY): Faeces are dark, liquid and gelatinous in the wild when feeding on a low-fibre diet of mainly seal blubber. Gut transit time varies depending on the diet, particularly the fat content, as indicated by a study in which transit times varied from 12.3 +/- 1.9 hours for a diet of fish and 13.8 +/- 5.4 hr for seal muscle and viscera to 38.0 +/- 8.0 hr for a diet of seal blubber and skin.

URINARY SYSTEM (URINE): --

CHROMOSOMES: 2n = 74 Chromosomes.

MUSCULO-SKELETAL SYSTEM: --

SPECIAL SENSES AND VOCALISATIONS: Polar bears have good vision; they may be able to see moving objects as far away as 3 - 5 km (2-3 miles) although stationary objects probably only are recognised to about 1 km (0.6 miles). Their hearing is also good. Their sense of smell is excellent and may be used to detect prey at a distance, even under snow. Adults vocalise (chuffing) mainly during agonistic behaviour; young nursing cubs will "chuckle".

(References are available in detailed literature reports below)

Feeding Behaviour

EDITORIAL SUMMARY

• Polar bears hunt their main prey, seals, mostly by still-hunting, waiting near a breathing hole, usually while lying down, for up to an hour (but for shorter times if sitting or standing). They also stalk seals, crawling slowly until about 15 - 30 m (50 -100 ft) from a basking seal, then making a final rush. Very rarely, seals are hunted while swimming. 
• Once a seal is killed, the bear will eat the blubber first, starting in the middle of the seal.
• Washing is considered to be an integral part of feeding behaviour; bears will alternately rinse and lick their paws and face at a pool of water.
• A bear does not always eat all of its kill; for inexperienced, recently-independent bears, scavenging on kills of older bears is probably important.
• In summer, in areas where seals are not available, polar bears hunt seabirds such as waterfowl, catching flightless Branta canadensis - Canada geese on land and coming up under birds sitting on the water. They have been found predating various nesting sea birds, eating eggs, chicks and adults.
• Polar bears also hunt small mammals and some will hunt large ungulates such as Rangifer tarandus - Reindeer and even Ovibos moschatus - Musk ox.
• When females and their cubs emerge from the maternity den, the female may dig for grasses, sedges and moss near the den in the first weeks while the family remains near the den.
• Polar bears are attracted to carcasses and congregate at large whale carcasses.
• Polar bears will scavenge in human rubbish dumps and field camps.

Further information on diet is provided in Polar bear Ursus maritimus - Natural Diet (Literature Reports)) 

(References are available in detailed literature reports below)

Parental Behaviour

EDITORIAL SUMMARY

• Immediately after parturition, the female licks the cub.
• Observations of a zoo bear showed that the mother lay on her side, keeping young cubs in a pocket formed between the chest and upper forelegs, and covered by her head and neck. To nurse newborn cubs, the female lay on her side or back; later, the female nursed her cubs while in a sitting position. Cubs were picked up and moved by a limb or with the cub's whole head in its mother's mouth. The female was often observed licking her cubs and presumably stimulating urination and defecation.
• In the wild, females and their cubs usually stay together for 2.5 years.
• Litter switching and adoptions occur occasionally in wild polar bears.

Further information on reproduction is provided in Polar bear Ursus maritimus - Life Stages (Literature Reports)

(References are available in detailed literature reports below)

Social Behaviour / Territoriality / Predation / Learning

EDITORIAL SUMMARY

• Home range sizes are very variable; some individuals may use only a few hundred square kilometres, while others may move several thousand kilometres annually and use over 500,000 square kilometres over their lifetimes.
• Population density estimates vary from one bear per 27 km² to one per 139 km². Along the coast of Hudson Bay, Ontario, there may be 0.1 - 0.5 bears per km of coastline (0.2 - 0.8 bears per mile). Maternity dens of females may be found at very high densities: one per 50 square metres.
• Polar bears are non-territorial; there is extensive overlap between home ranges. 
• Tracking studies use radio-transmitters. Collars are used on females, but easily slip over the head of males, since this is smaller in diameter than the neck. Ear-mounted transmitters have been used. Hair-mounted transmitters remain attached for only a short time. Transmitters have also been implanted subcutaneously, with either a subcutaneous antenna (limited range) or a percutaneous antenna.
• Polar bears caught in traps may watch warily, or slide slowly towards a human. Some may threaten, "growling, huffing, champing the teeth, and laying back their ears", and some will charge.
• The main social group is the family (mother and cubs). In winter, other polar bears are solitary. As the breeding season approaches, pairs may be seen together. In some regions where bears are ashore during summer, groups may be seen, mainly of adult males, who may be very tolerant of one another, even being seen in groups with bodies touching, and sometimes engaging in social play.
• Carcass remains from polar bear kills of seals are scavenged by Alopex lagopus - Arctic foxes and this may be important for arctic fox survival. Larus spp. gulls and Corvus corax - Common raven also scavenge from polar bears. Polar bears interact with Ursus arctos - Brown bears where their ranges overlap, but little is known about these interactions. One wild hybrid polar bear x Ursus arctos - Brown bear has been confirmed; a number have been bred in zoos.
• Polar bears have few predators. Adult male polar bears may kill cubs-of-the-year, yearlings and even sometimes adult females. Walrus Odobenus rosmarus, while sometimes taken as prey, also sometimes kill polar bears. Very rarely, wolves may kill a polar bear.
• Maternity dens are used by pregnant female polar bears to produce their cubs and raise them to about three months old. Other bears use dens or day nests for shorter periods. In summer, they use shallow pits or earth dens to get away from the heat and reduce problems with biting flies. In both autumn and winter they may use dens for up to about three months, possibly to avoid heat-stress during the ice-free period and/or winter to avoid inclement weather or to reduce energy expenditure when food availability is reduced.
• Learning is important for polar bear survival and continues throughout the time the cubs spend with their mother. Hunting methods are passed on by mothers to cubs. Polar bears show great curiosity towards new objects, and investigate them.

(References are available in detailed literature reports below)

Sexual Behaviour

EDITORIAL SUMMARY

• Polar bears are promiscuous. Because females mate only about every third year, in any one year more males than females are available to mate. A male may stay with a female for some days and the pair may mate several times. Several males may follow a female at one time and males may fight for access to a female. Males often attempt to isolate females from other males by herding them into remote areas.

(References are available in detailed literature reports below)

Activity Patterns, Self-grooming and Navigation

EDITORIAL SUMMARY

ACTIVITY PATTERNS: Polar bears are good swimmers, using their front legs for propulsion and their back legs as a rudder. They can swim distances as long as 65 km over open water. They can dive and swim underwater for up to two minutes. Usually they dive head-first, but when stalking in the water they just raise their head or nose out of the water then slip back under the surface. When lack of ice prevents hunting, polar bears can spend much of the time inactive.

SELF-GROOMING: Washing of the paws and face at a pool of water is an integral part of feeding behaviour. Polar bears also slide along snow to clean or dry wet fur.

CIRCADIAN RHYTHM: Polar bears may be active at any time of the day or night. Their activity follows that of their main prey; seals are most active in the morning, so polar bears are most active hunting at that time. They show longer hours of activity during the months when seals are most accessible. On coasts away from food sources in summer, polar bears may spend most of their time resting.

SPEED OF MOVEMENT: Polar bears can swim at about 10 km/hr (6.5 mph) and may reach 30-40 km/hr when running.

NAVIGATION: Polar bears have well-developed navigational abilities.

(References are available in detailed literature reports below)

General Habitat Type

EDITORIAL SUMMARY

• Polar bears may be considered marine mammals; they are found on coasts and pack ice, sometimes hundreds of kilometres from shore, most of the time. Individuals also may wander as far as 200 km inland.
• Polar bears need habitats which provide maternity denning areas, feeding areas, summer retreats and breeding areas; more than one of these functions may be met by the same area.
  • Preferred habitat for hunting is periodically active ice (movements and ice fracturing, followed by refreezing, due to wind and sea currents) causing intermittent lanes or patches of recently refrozen ice. This occurs in tidal zones along coastline, across the mouths of bays, and at the landfast ice/drifting pack ice interface.
  • Maternity denning areas must provide sufficient snow to cover the bear. For details see: Polar bear Ursus maritimus - Nests - Burrows - Shelters (Literature Reports)
  • For mating, polar bears may use certain land and ice formations - headlands, ice islands and pressure ridges as scent-posts, congregation sites and lookouts. 
  • In summer, polar bears use a variety of habitats, depending on sex and reproductive status as well as local conditions; coasts, offshore islands and inland habitats are all used.

(References are available in detailed literature reports below)

Nests / Burrows / Shelters

EDITORIAL SUMMARY

• Maternity dens are dug in the snow, usually on land but sometimes on pack ice. On land, they are usually within 8 km of the coast, but in some areas are at much greater distances away from the water. A maternity den may be a simple chamber with a tunnel leading to the surface, or may have several interconnected chambers. Sometimes they are dug over earth dens. Within the den the temperature may stay slightly above 0 °C (32 °F), while outside it may be as low as -50 °C (-58 °F).
• Polar bears also dig depressions or burrows in which to stay cool on land in summer, and dens in snow which are used for periods of a few weeks to three months in autumn and/or in winter. 

(References are available in detailed literature reports below)

Distribution and Movement (Migration etc.)

EDITORIAL SUMMARY

• Polar bears are found circumpolar in the arctic. 
• The limits of their range southward is determined by the distribution of pack ice and annual winter landfast ice. They may be found as far north as 88°N (and even further north) and as far south as 52 °N. Their southern limits reach in the Bering Sea to St Matthew Island and the Pribilof Islands, in Canada to the southeastern coast of Labrador, Newfoundland and the south of James' Bay, and in the North Atlantic to Iceland.
• The IUCN Polar Bear Specialist Group recognises 19 subpopulations of polar bears.
  • See: "Status of the polar bear" (P100.14.w1) [Full text included]

(References are available in detailed literature reports below)

Maps of their range are provided in B442 - Bears. Status Survey and Conservation Action Plan - Chapter 14 [full text provided] and "Status of the polar bear" (P100.14.w1) [Full text included]

Species variation

EDITORIAL SUMMARY

• There are no subspecies of polar bears.

(References are available in detailed literature reports below)

Conservation Status

EDITORIAL SUMMARY

WILD POPULATION - IMPORTANCE: The total world population of polar bears at present may exceed 20,000.

GENERAL LEGISLATION: Polar bears are protected under the 1973 Agreement on the Conservation of Polar Bears.

CITES LISTING: Appendix II

RED-DATA LIST STATUS: The most recent listing is Vulnerable. This change from the previous listing of Lower Risk, conservation dependent, is due to global warming, associated changes in polar bear habitat and expected substantial (>30%) population declines related to this.

THREATS: The main threat historically has been over-hunting. More recently, the implications of global warming have been recognised. This is expected to cause dramatic reductions in sea ice cover over the next 50 to 100 years, and in the quality of remaining sea ice. Polar bears, with their low reproductive rates and long generational spans are unlikely to be able to adapt well to significantly reduced ice coverage. Additional threats are associated with petroleum exploration, toxic chemicals such as PCBs, and nuclear waste storage.

PEST STATUS / PEST POPULATIONS: Polar bears may become nuisances when looking for human-associated food during the summer period when natural foods are scarce or unavailable.

CAPTIVE POPULATIONS: There are about 390 polar bears in zoos.

TRADE AND USE: Polar bears are hunted, including traditionally by local peoples.

For more information see: B442: Bears. Status Survey and Conservation Action Plan - full text provided

(References are available in detailed literature reports below)