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

Daily pattern

• Most active during mid-day, except during the onset of spring hunting season when peak activity shifts to overnight (Ware et al. 2020)
• Amount of time spent hunting changes, depending on season and availability of seals
  • Time-intensive; generally, less than 2% of hunting attempts are successful
• Self-grooming occurs after 30 minutes of feeding during summer

Yearly pattern

• Late February-April: mother and cubs leave den
  • Usually remain at den site for 7 to 10 days so cubs can adjust to cold conditions
    • Den may be 20 degrees warmer
• March-April: adult males begin to search for mates
• April-June: mating occurs over ~2-week period
  • Likely induces egg ovulation in females
  • Implantation of embryo delayed until autumn
• April-August: bears most active
  • Hunt Ringed Seals, especially pups, which are often born in April
• August-September:
  • Activity varies by ecoregion
    • Where sea ice remains, polar bears may continue hunting (although with less success during spring)
    • If forced to migrate from sea ice to land, may forage terrestrially, dig sleeping pits and temporary dens, and are generally less active than in the rest of the year (Messier et al. 1994)
• Late October-early November: denning by pregnant females begins, and the embryo implants into the uterus to begin pregnancy
  • In ecoregions where sea ice melts, polar bears migrate back onto the ice as it returns
• November-January: females give birth and begin nursing young in den

Adult females remain in a den for half the year or longer

(Atkinson & Ramsay 1995) (Folk et al 1976) (Kurt 1990)

• Prior to denning, pregnant females store energy by gaining massive amounts of body weight
• While denning, do not eat, drink, urinate, or defecate
• Body wastes are recycled biochemically, eliminating the need to urinate and preventing dehydration
• Most stored energy comes from burning body fat, which supplies 90% of energy used during denning
• Use of stored energy results in loss of about 40% of body weight (varies among individuals)
• Females may show site fidelity to quality den sites from year-to-year (e.g., Ramsay and Stirling 1990; Zeyl et al. 2010)
  • Zeyl et al. (2010) found that daughters tend to den in similar locations as their mothers
  • Females sometimes change locations (move locally or immigrate to new areas) to take advantage of better den sites

All polar bears use dens

(Harrington 1968) (Van de Velde et al 2003)

• Shelter-dens: for short term use by males and non-pregnantfemales (Schweinsburg 1979; Jonkel et al. 1992; Derocher 2010)
  • For during times of no Ringed Seals, bad weather (too hot or too cold), too many insects or other bears
    • May use from 0.5 - 4 months, according to data from Greenland in 1920s to the 1960s (Ferguson 2000)
  • Made of snow (similar to dens used for giving birth to cubs) or earth or natural shelters like caves or even suitable overhanging blocks of ice

Changes in physiology due to denning activity

(Nelson et al. 1980)

• Heart rate
  • Sleeping heart rate can fall as low as 8-10 beats/minute (Folk et al. 1980)
    • 40-50 beats/minute when active in summer
• Bone health
  • Cellular mechanisms prevent significant bone loss during prolonged denning period (Lennox and Goodship 2008; McGee-Lawrence et al 2008)
• Body temperature
  • Falls from 37–38 °C to 35 °C after giving birth (Whiteman et al. 2015)
  • Cellualr metabolism may be fine-tuned for thermoregulation (Welch et al. 2014)
    • Possess unique genes 
• Metabolism (Derocher et al. 1990; Whiteman et al. 2015; Whiteman et al. 2018)
  • Pregnant female polar bears seem to use biochemical adaptations to survive the long denning fast without ill health effects, similar to other bear species
  • Outside of maternal denning, polar bears are mostly incapable of using those biochemical adaptations and long fasts can cause health problems

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
• Multiple bears may simultaneously scavenge at the same large food resources, such as whale carcasses on the shoreline
  • Surprisingly, during summer and autumn, may be driven away from whale carcasses by smaller brown bears (Ursus arctos) (Miller et al. 2015)
    • Also see Feeding

Dominance interactions

• Dominance among males loosely based on size
• Risk of injury in male-male fights is high (Derocher et al 2005)
• Mothers with cubs may be out-competed by other bears for high quality foraging habitat (e.g., Pilfold et al. 2014)
  • In part, females may be avoiding males that might harm their cubs

Aggression

• Males compete intensely for breeding partners
  • Most females reproduce only once every 3 years; only a third of the females are available during any breeding season
• Male bears may kill cubs (a behavior also observed in other bear species)
  • Females defend cubs by challenging or attacking the much-larger male
  • Older cubs can sometimes 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

Home ranges and habitat use

• Larger home ranges than terrestrial carnivores
• Range size varies, depending on reliability of prey, and use of drifting sea ice vs. stationary ice or land-based habitats during summer (e.g., Ferguson et al. 1999; Auger-Méthé et al. 2016; Pagano et al. 2021)
  • Also body size and reproductive status (e.g., solitary females and mothers with cubs tend to have smaller home ranges)
• Movements and range size vary most when ice is freezing and breaking up (e.g., Cherry et al. 2013; McCall et al. 2015)
• Often large, overlapping home ranges among individuals
  • Except when activity centered on concentrated resources (e.g., access to carcasses discarded by native subsistence hunters)
  • Habitat use between males and females similar (e.g., Laidre et al. 2014)
• Some polar bears (e.g., in the Beaufort Sea) have expanded their ranges, likely due to loss of sea ice habitat (Auger-Méthé et al. 2016; Durner et al. 2019; Pagano et al. 2021)
  • Habitat use of some individuals shifted farther north and northeast
    • More time spent in open water

Migration

• Large movements in summer when seasonally move to shore as sea ice melts and retreats, and in autumn back onto ice to hunt (e.g., Parks et al. 2006; Cherry et al. 2013)
• May make extensive northern and southern migrations

Heat retention and loss

• Fur provides primary insulation
• Body fat also insulative but not as effective as blubber found in seals and other marine mammals (e.g., Pond et al. 1992)
• Body: low surface area-to-volume ratio favors heat retention
• Overheating
  • Overheat easily when running (i.e., speeds over 5 kph or 3.5 mph)
    • Wild polar bears very rarely run at these speeds (<3% of movements) (Whiteman et al. 2015; Pagano et al. 2018)
• Susceptibility to cold
  • Occurs in thin adults and young cubs up to 6 months old with little body fat
  • However, temperature when begin to shiver (lower critical temperature) not yet known
• Body temperature
  • As long as bear isn't exposed to wind, body temperature and metabolic rate remain normal at -37ºC (-35°F)
  • Body temperature drops to 31 to 35ºC (88 to 95ºF) when in winter dens (Harrington 1968; Whiteman et al. 2015)
• Metabolism
  • Polar Bear has a high metabolism, especially during active months (similar to other carnivores)
    • Varies with climate and season, as in all bears

Vocalizations

(Wemmer et al 1976; Cushing et al 1988)

• Polar bear sounds and vocalization descriptions, from Polar Bears International
• Bear vocalizations (and hearing) still being studied
  • Knowledge of the bears' hearing range important for establishing effects of noise disturbance on these bears (Owen 2007; Owen et al. 2021)
• 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 between adults
  • May signal stress or agitation
• Bears snort /chuff, growl, and chomp teeth when showing aggression
• Polar Bears raised in managed care "groaned and chuffed" when presented with underwater call of Ringed Seals, their preferred prey (Cushing et al. 1988)

Olfactory communication

• Highly developed sense of smell
  • Unusually large surface area inside snout; dedicated to sense of smell (Green et al. 2012)
  • Detect breathing holes of Ringed Seal from at least 1 kilometer (0.6 mi) away
• Use of pheromone scents not documented but probably present when males seek/track females on ice
  • Adult male may walk 10 km in a straight line in search of a breeding female

Visual communication

• Includes body language, including head movements, charging, and circling (e.g., near a kill)
• 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.
• Also see Vision

Walking and resting

• Adapted primarily for walking
  • Swimming incurs a higher metabolic cost than in most other semiaquatic mammals (Durner et al. 2011; Griffen 2018; Pagano et al. 2019)
    • Each swimming stroke requires 1.5 times as much energy as the stride of a walking polar bear
    • Estimated that swimming at the same speed as walking requires 5 times as much energy
• Move with ease and agility over rough terrain and jumbled ice floes
• Conserve energy when moving at slow speeds (e.g., Pagano et al. 2018a)
  • Prefer lying down and still-hunting to chasing prey due to energy costs of running
• Most plantigrade (soles flat to the ground) 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 per sec (25 mph)
  • Speed sacrificed in favor of tremendous strength/mobility of limb movement

Swimming and diving

• Excellent swimming ability, like other carnivores
  • However, is energetically costly
• Capable divers (Lønø 1970; Lone et al. 2018a)
  • By one report, dives of up to 5m (15 ft) most common
  • Can dive up to 14 m (46 ft)
• Swim using oar-like 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 2 km/hr (Pagano et al. 2012; Pilfold et al. 2016)
• Able to swim up to 15 miles easily
  • Adapted for swimming nearshore
• Can swim for multiple days, if needed (Durner et al. 2011; Pagano et al. 2012)
• Swimming more common during summer and fall/autumn, when smaller ice pack (Lone et al. 2018a)
• Females with cubs less likely to swim (Pilfold et al. 2017; Lone et al. 2018a)
  • Young cubs at risk of hypothermia and drowning
• As ice packs melt, bears in some areas swim farther across open water
  • Longest known sim: Durner et al. (2011) report a female polar bear swimming 687 km (427 mi) over 9 days (mild sea/weather conditions)
    • Lost cub and 22% of her body mass (insulation against cold)
  • DeMaster and Stirling (1981): report of a 40-mile swim across open water
• Longer swims may be becoming more common (e.g., Pagano et al. 2012)
  • Longer swims (hundreds of kilometers), especially in open seas with waves can be dangerous
    • Can result in drowning (Monnett and Gleason 2006)

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

• Ringed seals
  • Each year kill about 44% of newborn 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 unafraid (Stirling 1977, Amstrup 2003)
• Arctic foxes, ravens, gulls scavenge remains of seals killed by Polar Bears (Rosing 2006)
• Also see Diet & Feeding

A polar bear dives underwater at the San Diego Zoo.

Image credit: © San Diego Zoo Wildlife Alliance. All rights reserved.

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)