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Polar Bear (Ursus maritimus) Fact Sheet: Behavior & Ecology

Activity Cycle

Daily Pattern

  • Most active during first third of the day. Least active in last third.
  • In summer, grooming/washing occurs after 30 minutes of feeding.
  • Amount of time spent hunting changes depending on availability of seals.
    • In general, less than 2% of hunting attempts are successful.
    • An experienced adult catches a seal every 4-5 days.

Yearly pattern

  • Late February-April: mother and cubs leave den.
  • Usually remain at den site for 7-10 days so that cubs can adjust to cold (den may be 20 degrees warmer) and have a chance to exercise.
  • March-April: adult males begin search for females.
  • April-May: ovulation induced in female due to intense 1-2 week mating period.
  • April-August: bears most active. Ringed Seals give birth in April.
  • August-September: bears of both sexes dig sleeping pits and temporary dens and remain somewhat sedentary in Canadian Arctic (Messier et al 1994).
  • Late October-early November: denning by females.
  • Delayed implantation of embryo occurs in fall.
  • November-January: females give birth, nurse young in den.

Hibernation & Denning

Adult females remain in a den for at least half the year. (Atkinson & Ramsay 1995) (Folk et al 1976) (Kurt 1990)

  • In these months, do not eat, drink, urinate or defecate.
  • Body wastes recycled biochemically (without kidneys) to prevent dehydration.
  • As much as 30% of body mass lost; 43% of body weight
  • Massive weight gain before denning protects against extended fasting during pregnancy and denning.
  • Stored fat broken down to supply 90% of energy requirements.

All polar bears use dens. (Harrington 1968) (Van de Velde et al 2003)

  • Maternity dens - long term use over winter. (Watts and Hansen 1987) (Messier et al 1994)
    • For pregnancy, birth, and first months of cubs' life.
    • Average use: 6 months
    • Adult females excavate in snow throughout their ranges.
  • Shelter-dens - short term use autumn-spring by males and females (Schweinsburg 1979) (Jonkel et al 1992) (Derocher 2010)
    • During times of no Ringed Seals, bad weather (including too hot), too many insects or other bears.
    • Periods varying from 0.5 - 4 months, according data from Greenland in 1920's -1960's. (Ferguson 2000)
    • Made of snow or earth or natural shelters like caves or even suitable overhanging blocks of ice.
    • Use in dark winter not easily observed until advent of satellite telemetry (Ferguson et al 2000

Polar Bears alter their physiology throughout the year. (Nelson et al 1980)

  • Other bears' physiology more tied to seasons.
  • Switch between feeding and fasting metabolism at any time of year, depending on food supplies. (Derocher et al 1990) (Nelson et al 1984)
    • Begin fasting within 7-10 days after food is gone.
  • Avoid significant bone loss during prolonged hibernation. (Lennox and Goodship 2008) (McGee-Lawrence et al 2008)
    • Sleeping heart rates during hibernation as low as 8-10 beats/minute. (Folk et al 1980)
      • 40-50 beats/minute in summer.
  • Polar Bear body temperature during hibernation only slightly lower than their normal. (Harrington 1968) (Folk et al 1980)
  • Body temperature may be fine-tuned on a cellular level by varying levels of nitric oxide (Welch et al. 2014)
    • Genetic differences between polar and brown bears suggest that polar bears may have increased ability to regulate the production of this molecule which can influence whether energy from food is used to power cellular functions (in the form of ATP) or whether it is used to generate heat (thermogenesis)

Social Groups

General

  • Solitary except for females with cubs.
  • Cubs learn by following and imitating mother during the 2.5 year period they are with her.
  • Sexes come together only briefly for up to two weeks during mating season, March-June (may remain together for up to two weeks).
  • Several bears may scavenge at the same whale carcass but each animal behaves independently.

Aggression

  • Most females reproduce only once every 3 years.
    • Only a third of the females are available during any breeding season
    • Males compete intensely for breeding partners.
  • Male bears of all species sometimes kill cubs.
    • Females will defend cubs by challenging or attacking a male twice her size
    • A 6 month-old cub can outrun an adult male.
  • In late fall when male bears fast and wait for ice to freeze, display little aggression but engage in mock ritualized battles.
  • A "loose dominance hierarchy" among males is based on size; risk of injury in male/male fights is high. (Derocher et al 2005)

Hunting

  • More predatory than other bears (less omnivorous).
  • Locate birth lairs and breathing holes of Ringed Seals by smell and sound.
    • Approach slowly to minimize their own sound.
    • May break into lair immediately or wait motionless for several hours for seal to return.
    • Studies on polar bear hearing of bears raised in managed care indicate that "auditory cues play an important role" (Cushing et al 1988)
    • Swim underwater to stalk seals lying at the edge of an ice floe.
  • Hunting in summer months: 77% still-hunting, 23% stalking.
  • Hunting in winter and early spring: almost all hunting is still-hunting (far more successful than stalking).
  • Small size of major prey probably eliminates any advantage in group hunting
    • Large numbers of bears scavenge together at a whale carcass or human garbage dump.
  • Consume fat of prey first (to get the most calories quickly).
  • Considerable competition between Polar Bears for a kill; larger bears will run off smaller bears.
  • Wash and lick themselves while feeding; spend up to 15 minutes grooming afterward.

Territorial Behavior

Home range

  • Large overlapping home ranges.
    • Varies greatly in drifting sea ice

Migration

  • May make extensive northern and southern migrations

Thermoregulation

Retaining and losing heat

  • In bears, the basal metabolic rate varies with climate and season
    • Polar Bear has the highest
  • Overheat easily when running; can't travel any great distance at speeds more than a walk.
    • Low surface-area to volume ratio favors heat retention.
    • Tendency to overheat enhanced by thick layer of fat
    • Thin adults and young cubs up to 6 months old, with little body fat, are susceptible to cold.
  • Use more than twice the predicted energy for moving at a given speed, perhaps due to bulky body.
  • Fat and fur both insulate.
  • As long as bear isn't exposed to wind, body temperature and metabolic rate remain normal at -37 degrees C (-35 degrees F).
  • Body temperature drops to 31-35 degrees C (88-95 degrees) when in winter dens; this temperature is only slightly below normal body temperature. (Harrington 1968)

Communication

Vocalization (Wemmer et al 1976; Cushing et al 1988)

Audio of polar bears, from Polar Bears International.

  • Bear vocalization (and hearing) not well known.
    • Knowledge of the bears' hearing range important for establishing effects of noise disturbance on these bears. (Owen 2007)
  • Females and cubs use chuffing call with each other.
    • 1-32 low intensity sound pulses emitted in rapid succession
    • Most frequent in cub's early months.
  • Chuffing call infrequent in adults; may signal stress/agitation.
  • Bears snort /chuff, growl, and chomp teeth when aggressive
  • Polar Bears raised in managed care "groaned and chuffed" when presented with underwater call of Ringed Seals (their favored prey). (Cushing et al 1988)
  • Preliminary investigations of acoustic communication in Polar Bears indicate they can produce low frequency sounds. (Owen 2009)

Olfactory and visual signals

  • Highly developed sense of smell.
    • Detect breathing holes of Ringed Seal from at least 1 kilometer (.6 mi)
  • Use of scents (pheromones) not documented but probably present when males seek females.
    • Adult male may walk 10 km in a straight line in search of a breeding female's track.
    • Once track crossed, recognition is instantaneous and he will proceed until he catches up to her.
  • Limited number of visual facial signals. (Kurt 1990)
    • Facial muscles poorly developed.
    • Unlike highly social cats and wolves, solitary lifestyle doesn't require elaborate mechanisms for group coexistence.

Locomotion

Walking and resting

  • Most plantigrade (soles flat to the ground similar to humans) of all the Carnivora.
    • Dogs and cats are digitigrade (stand on toes with most of sole elevated).
    • Digitigrade animals tend to be faster than plantigrade animals partly because of a longer stride.
  • Top speed recorded: 11 m/sec (25 mph).
    • Top speed for digitigrade lion and wolf: 35-40 mi/hr.
    • Speed sacrificed in favor of tremendous strength/mobility of limb movement
  • Prefer lying down and still-hunting to chasing prey due to energy costs of running.
  • Move with ease and agility over rough terrain and jumbled ice floes.

Swimming

  • Nearly all carnivores are excellent swimmers; polar bear has oarlike forepaws.
    • Forelimbs and large forepaws propel animal forward with a stroke like a dog swimming
    • Hind limbs trail behind serving as a rudder.
    • Head and shoulders held above water.
  • Swimming rate about 6.5 km/hr.
  • Able to swim up to 15 miles easily.
    • Adapted for swimming near-shore.
    • Some reports of longer swims in recent years.
      • DeMaster and Stirling (1981) - 40 mile swim across open water.
      • Longer swims, especially in open seas with waves can be dangerous
    • As ice packs melt, bears in some areas swim farther across open water
      • Researchers report a radio-collared female in the Beaufort Sea swam continuously for 687 km (427 miles) over 9 days and then swam and walked an additional 1,800 km (1,118 mi); she lost 22% of her body mass and her yearling cub (Durner et al. 2011)
    • Reports on the increase of bear drownings.

Interspecies Interactions

(DeMaster & Stirling 1981) (Regehr et al 2007) (Rosing 2006) (Stirling 1977, 1993) (Amstrup 2003)

  • Ringed seals
    • Each year kill about 44% of new-born Ringed Seal pups
    • Population size largely determined by numbers and availability of Ringed Seals
    • Ringed Seals, the Polar Bear's primary prey, have evolved into very cautious, vigilant animals; by contrast Weddel Seals living without ground predators in the Antarctic are comparatively fearless. (Stirling 1977, Amstrup 2003)
  • Arctic foxes, ravens, gulls scavenge remains of seals killed by Polar Bears (Rosing 2006).

Excellent Swimmers

polar bear under water

Polar Bear Plunge at the San Diego Zoo.

Image credit: © San Diego Zoo Global. All rights reserved.

Page Citations

Atkinson & Ramsay (1995)
Cushing et al (1988)
DeMaster & Stirling (1981)
Derocher (2010)
Durner et al. (2011)
Ferguson et al (2000)
Folk et al (1976)
Folk et al (1980)
Ginsburg (1994)
Gittleman (1989)
Herrington (1963, 1968)
Jonkel et al (1972)
Kurt (1990)
McGee-Lawrence et al (2008)
Megan (2009)
Messier et al (1994)
Nowak (1981)
Owen (2009)
Schweinsburg (1979)
Stirling (1993, 1998)
Van de Velde et al (2003)
Watts and Hansen (1987)
Welch et al. (2014)
Wemmer (1976)

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