Editing Polar bear (section)

==Behaviour and ecology==
Polar bears may travel areas as small as {{cvt|3500|km2}} to as large as {{cvt|38000|km2}} in a year, while drifting ice allows them to move further.<ref>{{cite journal|last1=Auger-Méthé|first1=M.|last2=Lewis|first2=M. A.|last3=Derocher|first3=A. E.|year=2016|title=Home ranges in moving habitats: polar bears and sea ice|journal=Ecography|volume=32|issue=1|pages=26–35|doi=10.1111/ecog.01260|bibcode=2016Ecogr..39...26A }}</ref> Depending on ice conditions, a bear can travel an average of {{cvt|12|km}} per day.<ref>{{cite journal|last1=Ferguson|first1=S. H.|last2=Taylor|first2=M. K.|last3=Born|first3=E. W.|last4=Rosing-Asvid|first4=A.|last5=Messier|first5=F.|year=2001|title=Activity and movement patterns of polar bears inhabiting consolidated versus active pack ice|journal=Arctic|volume=54|issue=1|pages=49–54|doi=10.14430/arctic763|doi-access=free}}</ref> These movements are powered by their energy-rich diet.{{sfn|Derocher|2012|p=12}} Polar bears move by walking and [[galloping]] and do not [[trot]].<ref>{{cite journal|last1=Gasc|first1=J-P|last2=Abourachid|first2=A|year=1997|title=Kinematic analysis of the locomotion of the polar bear (''Ursus maritimus'', Phipps, 1774) in natural and experimental conditions|journal=Netherlands Journal of Zoology|volume=48|issue=2|pages=145–167|doi=10.1163/156854298X00156}}</ref> Walking bears tilt their front paws towards each other.{{sfn|Derocher|2012|p=21}} They can run at estimated speeds of up to {{cvt|40|km/h}}<ref name="Brook"/> but typically move at around {{cvt|5.5|km/h}}.{{sfn|Stirling|2011|p=140}} Polar bears are also capable swimmers and can swim at up to {{cvt|6|km/h}}.{{sfn|Ellis|2009|p=88}} One study found they can swim for an average of 3.4 days at a time and travel an average of {{cvt|154.2|km}}.<ref>{{cite journal|last1=Pagano|first1=A. M.|last2=Durner|first2=G M.|last3=Amstrup|first3=S. C.|last4=Simac|first4=K. S.|last5=York|first5=G. S.|year=2012|title=Long-distance swimming by polar bears (''Ursus maritimus'') of the southern Beaufort Sea during years of extensive open water|journal=Canadian Journal of Zoology|volume=90|issue=5|pages=663–676|doi=10.1139/Z2012-033|bibcode=2012CaJZ...90..663P |url=https://zenodo.org/record/1235909 }}</ref> They can dive for as long as three minutes.<ref name="Stirling & van Meurs 2015">{{cite journal|last1=Stirling|first1=Ian|last2=van Meurs|first2=Rinie|title=Longest recorded underwater dive by a polar bear|journal=Polar Biology|volume=38|issue=8|date=2015|pages=1301–1304|doi=10.1007/s00300-015-1684-1|bibcode=2015PoBio..38.1301S |s2cid=6385494}}</ref> When swimming, the broad front paws do the paddling, while the hind legs play a role in steering and diving.<ref name="DeMaster1981"/>{{sfn|Derocher|2012|p=21}}
[[File:Mother cubs.JPG|thumb|right|Mother bear and cubs sleeping]]
Most polar bears are active year-round. [[Hibernation]] occurs only among pregnant females.{{sfn|Derocher|2012|p=28}} Non-hibernating bears typically have a normal [[Circadian rhythm|24-hour cycle]] even during days of [[Polar night|all darkness]] or [[Midnight sun|all sunlight]], though cycles less than a day are more common during the former.<ref>{{cite journal|last1=Ware|first1=J. V.|last2=Rode|first2=K. D.|last3=Robbins|first3=C. T.|last4=Leise|first4=T.|last5=Weil|first5=C. R.|last6=Jansen|first6=H. T.|year=2020|title=The clock keeps ticking: circadian rhythms of free-ranging polar bears|journal=Journal of Biological Rhythms|volume=35|issue=2|pages=180–194 |doi=10.1177/0748730419900877|pmid=31975640 |s2cid=210882454 |doi-access=free|bibcode=2020JBioR..35..180W }}</ref> The species is generally [[Diurnality|diurnal]], being most active early in the day.<ref>{{cite journal|last1=Stirling|first1=I.|year=1974|title=Midsummer observations on the behavior of wild polar bears (''Ursus maritimus'')|journal=Canadian Journal of Zoology|volume=52|issue=9|pages=1191–1198|doi=10.1139/z74-157|bibcode=1974CaJZ...52.1191S }}</ref> Polar bears sleep close to eight hours a day on average.{{sfn|Stirling|2011|p=141}} They will sleep in various positions, including curled up, sitting up, lying on one side, on the back with limbs spread, or on the belly with the rump elevated.{{sfn|Ellis|2009|p=79}}{{sfn|Stirling|2011|p=140}} On sea ice, polar bears snooze at [[Pressure ridge (ice)|pressure ridges]] where they dig on the sheltered side and lie down. After a snowstorm, a bear may rest under the snow for hours or days. On land, the bears may dig a resting spot on gravel or sand beaches.{{sfn|Stirling|2011|pp=140–141}} They will also sleep on rocky outcrops.{{sfn|Derocher|2012|p=68}} In mountainous areas on the coast, mothers and subadults will sleep on slopes where they can better spot another bear coming.{{sfn|Stirling|2011|p=141}} Adult males are less at risk from other bears and can sleep nearly anywhere.{{sfn|Derocher|2012|p=68}}

===Social life===
[[File:Play fight of polar bears edit 1.ogv|thumb|right|Young bears play-fighting]]
Polar bears are typically solitary, aside from mothers with cubs and mating pairs.{{sfn|Stirling|2011|p=105}} On land, they are found closer together and gather around food resources. Adult males, in particular, are more tolerant of each other in land environments and outside the breeding season.<ref name=Derocher1990>{{cite journal|last1=Derocher|first1=A. E.|last2=Stirling|first2=I.|year=1990|title=Observations of aggregating behaviour in adult male polar bears (''Ursus maritimus'')|journal=Canadian Journal of Zoology|volume=68|issue=7|pages=1390–1394|doi=10.1139/z90-207|bibcode=1990CaJZ...68.1390D }}</ref><ref name=Ferguson1997>{{cite journal|last1=Ferguson|first1=S. H.|last2=Taylor|first2=M. K.|last3=Messier|first3=F.|year=1997|title=Space use by polar bears in and around Auyuittuq National Park, Northwest Territories, during the ice-free period|journal=Canadian Journal of Zoology|volume=75|issue=10|pages=1585–1594|doi=10.1139/z97-785|bibcode=1997CaJZ...75.1585F }}</ref> They have been recorded forming stable "alliances", travelling, resting and playing together. A [[dominance hierarchy]] exists among polar bears with the largest mature males ranking at the top. Adult females outrank subadults and adolescents and younger males outrank females of the same age. In addition, cubs with their mothers outrank those on their own.<ref name=Ovsyanikov2005>{{cite journal|last=Ovsyanikov|first=N. G.|year=2005|title=Behavior of polar bears in coastal congregations|journal=Zoologicheskiĭ Zhurnal|volume=84|issue=1|pages=94–103|url=https://www.arlis.org/docs/vol1/E/Walrus/Russian/Ovsyanikov.2005.BehaviorPolarBearCoastalCongreg.ZoolZhurnal.pdf}}</ref> Females with dependent offspring tend to stay away from males,<ref name=Ferguson1997/> but are sometimes associated with other female–offspring units, creating "composite families".<ref name=Ovsyanikov2005/>

Polar bears are generally quiet but can produce various sounds.{{sfn|Derocher|2012|p=30}} [[Prusten|Chuffing]], a soft pulsing call, is made by mother bears presumably to keep in contact with their young.<ref name=Wemmer1976/> During the breeding season, adult males will chuff at potential mates.{{sfn|Derocher|2012|p=31}} Unlike other animals where chuffing is passed through the nostrils, in polar bears it is emitted through a partially open mouth.<ref name=Wemmer1976>{{cite journal|last1=Wemmer|first1=C.|last2=Von Ebers|first2=M.|last3=Scow|first3=K.|year=1976|title=An analysis of the chuffing vocalization in the polar bear (''Ursus maritimus'')|journal=Journal of Zoology|volume=180|issue=3|pages=425–439|doi=10.1111/j.1469-7998.1976.tb04686.x}}</ref> Cubs will cry for attention and produce humming noises while nursing.<ref>{{cite journal|last1=Derocher|first1=A. E.|last2=Van Parijs|first2=S. M.|last3=Wiig|first3=Ø|year=2010|title=Nursing vocalization of a polar bear cub|journal=Ursus|volume=21|issue=2|pages=189–191|doi=10.2192/09SC025.1|s2cid=55599722}}</ref> Teeth chops, jaw pops, blows, huffs, moans, [[growling|growls]] and [[roar]]s are heard in more hostile encounters.{{sfn|Derocher|2012|p=31}} A polar bear visually communicates with its eyes, ears, nose and lips.<ref name=Ovsyanikov2005/> Chemical communication can also be important: bears secrete their scent from their foot pads into their tracks, allowing individuals to keep track of one another.<ref>{{cite journal |author1=Owen, M. A. |author2=Swaisgood, R. R. |author3=Slocomb, C. |author4=Amstrup, S. C. |author5=Durner, G. M. |author6=Simac, K. |author7=Pessier, A. P. |year=2014 |title=An experimental investigation of chemical communication in the polar bear |journal=Journal of Zoology |volume=295 |issue=1 |pages=36–43 |doi=10.1111/jzo.12181}}</ref>

===Diet and hunting===
[[File:Polar bear (Ursus maritimus) with its prey.jpg|thumb|right|Bear feeding on a [[bearded seal]]]]
The polar bear is a [[hypercarnivore]],<ref name=Sacco2004/> and the most carnivorous species of bear.<ref name=Slater2010/> It is an [[apex predator]] of the Arctic,{{sfn|Stirling|2011|p=155}} preying on [[Ice seal|ice-living seals]] and consuming their energy-rich [[blubber]].{{sfn|Derocher|2012|p=69}} The most commonly taken species is the [[ringed seal]], but they also prey on [[bearded seal]]s and [[harp seal]]s.<ref name="DeMaster1981"/> Ringed seals are ideal prey as they are abundant and small enough to be overpowered by even small bears.{{sfn|Stirling|2011|pp=155–156}} Bearded seal adults are larger and are more likely to break free from an attacking bear, hence adult male bears are more successful in hunting them. Less common prey are [[hooded seal]]s, [[spotted seal]]s, [[ribbon seal]]s and the more temperate-living [[harbor seal|harbour seal]]s.{{sfn|Derocher|2012|pp=73, 76–77}} Polar bears, mostly adult males, will occasionally hunt [[walrus]]es both on land and ice. They mainly target young walruses, as adults, with their thick skin and long tusks, are too large and formidable.{{sfn|Stirling|2011|p=161}}

Besides seals, bears will prey on [[cetacea]]n species such as [[beluga whale]]s and [[narwhal]]s, as well as [[reindeer]], birds and their eggs, fish and [[marine invertebrates]].{{sfn|Derocher|2012|pp=80–88}} They rarely eat plant material as their digestive system is too specialized for animal matter,<ref>{{cite journal |last1=Ramsay |first1=M. A. |last2=Hobson |first2=K. A. |date=May 1991 |title=Polar bears make little use of terrestrial food webs: evidence from stable-carbon isotope analysis |volume=86 |issue=4 |pages=598–600 |doi=10.1007/BF00318328 |pmid=28313343 |journal=Oecologia|bibcode=1991Oecol..86..598R |s2cid=32221744 }}</ref> though they have been recorded eating berries, moss, grass and [[seaweed]].{{sfn|Derocher|2012|pp=88–89}} In their southern range, especially near Hudson Bay and James Bay, polar bears endure all summer without sea ice to hunt from and must subsist more on terrestrial foods.<ref name="ReferenceB">{{cite journal |last1=Russell |first1=Richard H. |title=The food habits of polar bears of James Bay and Southwest Hudson Bay in summer and autumn |journal=Arctic |date=1975|volume=28 |issue=2 |pages=117–129 |doi=10.14430/arctic2823 |doi-access=free }}</ref> Fat reserves allow polar bears to survive for months without eating.{{sfn|Ellis|2009|p=89}} [[Cannibalism]] is known to occur in the species.<ref name=Taylor1985/>

Polar bears hunt their prey in several different ways. When a bear spots a seal [[Hauling-out|hauling out]] on the sea ice, it slowly stalks it with the head and neck lowered, possibly to make its dark nose and eyes less noticeable. As it gets closer, the bear crouches more and eventually charges at a high speed, attempting to catch the seal before it can escape into its ice hole. Some stalking bears need to move through water; traversing through water cavities in the ice when approaching the seal or swimming towards a seal on an ice floe. The polar bear can stay underwater with its nose exposed. When it gets close enough, the animal lunges from the water to attack.{{sfn|Stirling|2011|pp=170–171}}

During a limited time in spring, polar bears will search for ringed seal pups in their birth lairs underneath the ice. Once a bear catches the scent of a hiding pup and pinpoints its location, it approaches the den quietly to not alert it. It uses its front feet to smash through the ice and then pokes its head in to catch the pup before it can escape. A ringed seal's lair can be more than {{cvt|1|m}} below the surface of the ice and thus more massive bears are better equipped for breaking in. Some bears may simply stay still near a breathing hole or other spot near the water and [[sit-and-wait predators|wait]] for prey to come by.{{sfn|Derocher|2012|pp=127–129, 131}} This can last hours and when a seal surfaces the bear will try to pull it out with its paws and claws.{{sfn|Ellis|2009|p=91}} This tactic is the primary hunting method from winter to early spring.<ref name="DeMaster1981"/>
[[File:Polar Bear ANWR 10.jpg|thumb|left|Bear with whale carcass]]
Bears hunt walrus groups by provoking them into stampeding and then look for young that have been crushed or separated from their mothers during the turmoil.{{sfn|Stirling|2011|p=161}} There are reports of bears trying to kill or injure walruses by throwing rocks and pieces of ice on them.<ref>{{cite journal|last1=Stirling|first1=I.|last2=Laidre|first2=K. L.|last3=Born|first3=E. W.|year=2021|title=Do wild polar bears (''Ursus maritimus'') use tools when hunting walruses (''Odobenus rosmarus'')?|journal=Arctic|volume=74|issue=2|pages=175–187|doi=10.14430/arctic72532|s2cid=236227117|doi-access=free}}</ref> Belugas and narwhals are vulnerable to bear attacks when they are stranded in shallow water or stuck in isolated breathing holes in the ice.{{sfn|Derocher|2012|pp=80–83}} When stalking reindeer, polar bears will hide in vegetation before an ambush.<ref name="Brook">{{cite journal |last1=Brook |first1=R. K. |last2=Richardson |first2=E. S. |year=2002 |title=Observations of polar bear predatory behaviour toward caribou |journal=Arctic |volume=55 |issue=2 |pages=193–196 |doi=10.14430/arctic703|doi-access=free }}</ref> On some occasions, bears may try to catch prey in open water, swimming underneath a seal or [[aquatic bird]]. Seals in particular, however, are more agile than bears in the water.{{sfn|Derocher|2012|pp=84–85, 132}} Polar bears rely on raw power when trying to kill their prey, and will employ bites and paw swipes.<ref name=Sacco2004>{{cite journal|last1=Sacco|first1=T.|last2=Van Valkenburgh|first2=B.|year=2004|title=Ecomorphological indicators of feeding behaviour in the bears (Carnivora: Ursidae)|journal=Journal of Zoology|volume=263|issue=1|pages=41–54|doi=10.1017/S0952836904004856}}</ref> They have the strength to pull a mid-sized seal out of the water or haul a beluga carcass for quite some distance.{{sfn|Ellis|2009|p=112}} Polar bears only occasionally [[Hoarding (animal behavior)|store]] food for later—burying it under snow—and only in the short term.<ref>{{cite journal|last1=Stirling|first1=I.|last2=Laidre|first2=K. L.|last3=Derocher|first3=A. E.|last4=Van Meurs|first4=R.|year=2020|title=The ecological and behavioral significance of short-term food caching in polar bears (''Ursus maritimus'')|journal=Arctic Science|volume=6|issue=1|pages=41–52|doi=10.1139/as-2019-0008|s2cid=209575444}}</ref>

[[Arctic fox]]es routinely follow polar bears and scavenge scraps from their kills. The bears usually tolerate them but will charge a fox that gets too close when they are feeding. Polar bears themselves will scavenge. Subadult bears will eat remains left behind by others. Females with cubs often abandon a carcass when they see an adult male approaching, though are less likely to if they have not eaten in a long time.{{sfn|Stirling|2011|pp=191–193}} Whale carcasses are a valuable food source, particularly on land and after the sea ice melts, and attract several bears.<ref name=Derocher1990/> In one area in northeastern Alaska, polar bears have been recorded competing with [[grizzly bear]]s for whale carcasses. Despite their smaller size, grizzlies are more aggressive and polar bears are likely to yield to them in confrontations.<ref>{{cite journal|last1=Miller|first1=S.|last2=Wilder|first2=J.|last3=Wilson|first3=R. R.|year=2015|title=Polar bear–grizzly bear interactions during the autumn open-water period in Alaska|journal=Journal of Mammalogy|volume=96|issue=6|pages=1317–1325|doi=10.1093/jmammal/gyv140|doi-access=free}}</ref> Polar bears will also scavenge at garbage dumps during ice-free periods.<ref>{{cite journal|last1=Lunn|first1=N. J.|last2=Stirling|first2=I.|year=1985|title=The significance of supplemental food to polar bears during the ice-free period of Hudson Bay|journal=Canadian Journal of Zoology|volume=63|issue=10|pages=2291–2297|doi=10.1139/z85-340|bibcode=1985CaJZ...63.2291L }}</ref>

===Reproduction and development===
[[File:Встреча 2.jpg|thumb|right|Courting male approaching female]]
Polar bear mating takes place on the sea ice and during spring, mostly between March and May.<ref name="DeMaster1981"/><ref name=Ramsay1986>{{cite journal|last1=Ramsay|first1=M. A.|last2=Stirling|first2=I.|year=1986|title=On the mating system of polar bears|journal=Canadian Journal of Zoology|volume=64|issue=10|pages=2142–2151|doi=10.1139/z86-329|bibcode=1986CaJZ...64.2142R }}</ref><ref name=Derocher2010/>{{sfn|Stirling|2011|p=105}} Males search for females in [[estrus]] and often travel in twisting paths which reduces the chances of them encountering other males while still allowing them to find females. The movements of females remain linear and they travel more widely.<ref>{{cite journal|last1=Laidre|first1=K. L.|last2=Born|first2=E. W.|last3=Gurarie|first3=E.|last4=Wiig|first4=Ø|last5=Dietz|first5=R.|last6=Stern|first6=H.|year=2013|title=Females roam while males patrol: divergence in breeding season movements of pack-ice polar bears (''Ursus maritimus'')|journal=Proceedings of the Royal Society B: Biological Sciences|volume=280|issue=1752 |page=20122371|doi=10.1098/rspb.2012.2371|pmid=23222446 |pmc=3574305 }}</ref> The mating system can be labelled as female-defence [[Polygyny in animals|polygyny]], [[serial monogamy]] or [[Promiscuity#Other animals|promiscuity]].<ref name=Derocher2010>{{cite journal|last1=Derocher|first1=A. E.|last2=Anderson|first2=M.|last3=Wiig|first3=Ø|last4=Aars|first4=J.|year=2010|title=Sexual dimorphism and the mating ecology of polar bears (Ursus maritimus) at Svalbard (''Ursus maritimus'') at Svalbard|journal=Behavioral Ecology and Sociobiology|volume=64|issue=6|pages=939–946|doi=10.1007/s00265-010-0909-0|s2cid=36614970 }}</ref><ref name=Zey2009/>

Upon finding a female, a male will try to isolate and guard her. Courtship can be somewhat aggressive, and a male will pursue a female if she tries to run away. It can take days for the male to mate with the female which [[Induced ovulation (animals)|induces ovulation]]. After their first copulation, the couple bond. Undisturbed polar bear pairings typically last around two weeks during which they will sleep together and mate multiple times.{{sfn|Derocher|2012|pp=141, 145–147}} Competition for mates can be intense and this has led to [[sexual selection]] for bigger males. Polar bear males often have scars from fighting.<ref name=Ramsay1986/><ref name=Derocher2010/> A male and female that have already bonded will flee together when another male arrives.{{sfn|Derocher|2012|pp=145–147}} A female mates with multiple males in a season and a single litter can have more than one father.<ref name=Zey2009>{{cite journal|last1=Zeyl|first1=E.|last2=Aars|first2=J.|last3=Ehrich|first3=D.|last4=Bachmann|first4=L.|last5=Wiig|first5=Ø|year=2009|title=The mating system of polar bears: a genetic approach|journal=Canadian Journal of Zoology|volume=87|issue=12|pages=1195–1209|doi=10.1139/Z09-107|bibcode=2009CaJZ...87.1195Z }}</ref> 
[[File:Polar bear cubs in the snow.jpg|thumb|left|Polar bear cubs]]
When the mating season ends, the female will build up more fat reserves to sustain both herself and her young. Sometime between August and October, the female constructs and enters a [[maternity den]] for winter. Depending on the area, maternity dens can be found in sea ice just off the coastline or further inland and may be dug underneath snow, earth or a combination of both.{{sfn|Stirling|2011|pp=112, 115, 120}} The inside of these shelters can be around {{cvt|1.5|m}} wide with a ceiling height of {{cvt|1.2|m}} while the entrance may be {{cvt|2.1|m}} long and {{cvt|1.2|m}} wide. The temperature of a den can be much higher than the outside.{{sfn|Ellis|2009|p=85}} Females hibernate and give birth to their cubs in the dens.{{sfn|Derocher|2012|pp=28, 155}} Hibernating bears [[fasting|fast]] and internally recycle bodily waste. Polar bears experience [[delayed implantation]] and the fertilized embryo does not start development until the fall, between mid-September and mid-October.{{sfn|Stirling|2011|p=124}} With delayed implantation, [[gestation]] in the species lasts seven to nine months but actual pregnancy is only two months.{{sfn|Derocher|2012|p=171}}

Mother polar bears typically give birth to two cubs per litter. As with other bear species, newborn polar bears are tiny and [[Precociality and altriciality|altricial]].{{sfn|Stirling|2011|pp=124–125, 131}} The newborns have woolly hair and pink skin, with a weight of around {{cvt|600|g}}.<ref name="DeMaster1981"/>{{sfn|Derocher|2012|p=10}} Their eyes remain closed for a month.{{sfn|Ellis|2009|p=84}} The mother's fatty milk fuels their growth, and the cubs are kept warm both by the mother's body heat and the den. The mother emerges from the den between late February and early April, and her cubs are well-developed and capable of walking with her.{{sfn|Stirling|2011|pp=126–127}} At this time they weigh {{cvt|10|–|15|kg}}.<ref name="DeMaster1981"/> A polar bear family stays near the den for roughly two weeks; during this time the cubs will move and play around while the mother mostly rests. They eventually head out on the sea ice.{{sfn|Stirling|2011|p=128}}
[[File:Cub polar bear is nursing 2.OGG|thumb|right|Mother nursing her young]]
Cubs under a year old stay close to their mother. When she hunts, they stay still and watch until she calls them back.{{sfn|Derocher|2012|pp=173, 184}} Observing and imitating the mother helps the cubs hone their hunting skills.{{sfn|Stirling|2011|p=186}} After their first year they become more independent and explore. At around two years old, they are capable of hunting on their own.{{sfn|Derocher|2012|p=184}} The young suckle their mother as she is lying on her side or sitting on her rump.{{sfn|Stirling|2011|p=128}} A [[lactating]] female cannot conceive and give birth,{{sfn|Derocher|2012|p=181}} and cubs are weaned between two and two-and-a-half years.<ref name="DeMaster1981"/> She may simply leave her weaned young or they may be chased away by a courting male.{{sfn|Derocher|2012|p=184}} Polar bears reach sexual maturity at around four years for females and six years for males.{{sfn|Stirling|2011|pp=128–129}} Females reach their adult size at 4 or 5 years of age while males are fully grown at twice that age.{{sfn|Derocher|2012|p=185}}

===Mortality===
Polar bears can live up to 30 years.<ref name="DeMaster1981"/> The bear's long lifespan and ability to consistently produce young offsets cub deaths in a population. Some cubs die in the dens or the womb if the female is not in good condition. Nevertheless, the female has a chance to produce a surviving litter the next spring if she can eat better in the coming year. Cubs will eventually starve if their mothers cannot kill enough prey.{{sfn|Stirling|2011|pp=204–207}} Cubs also face threats from [[wolves]]<ref>{{cite journal|last1=Richardson|first1=E. S.|last2=Andriashek|first2=D.|year=2006|title=Wolf (''Canis lupus'') predation of a polar bear (''Ursus maritimus'') cub on the sea ice off northwestern Banks Island, Northwest Territories, Canada|journal=Arctic|volume=59|issue=3|pages=322–324|doi=10.14430/arctic318|doi-access=free}}</ref> and adult male bears. Males [[infanticide (zoology)|kill cubs]] to bring their mother back into estrus but also kill young outside the breeding season for food.<ref name=Taylor1985>{{cite journal|last1=Taylor|first1=M.|last2=Larsen|first2=T.|last3=Schweinsburg|first3=R. E.|year=1985|title=Observations of intraspecific aggression and cannibalism in polar bears (''Ursus maritimus'')|journal=Arctic|volume=38|issue=4|pages=303–309|doi=10.14430/arctic2149|doi-access=free}}</ref> A female and her cubs can flee from the slower male. If the male can get close to a cub, the mother may try to fight him off, sometimes at the cost of her life.{{sfn|Stirling|2011|p=212}}

Subadult bears, who are independent but not quite mature, have a particularly rough time as they are not as successful hunters as adults. Even when they do succeed, their kill will likely be stolen by a larger bear. Hence subadults have to scavenge and are often underweight and at risk of starvation. At adulthood, polar bears have a high survival rate, though adult males suffer injuries from fights over mates.{{sfn|Stirling|2011|pp=207–208}} Polar bears are especially susceptible to ''[[Trichinella]]'', a parasitic [[roundworm]] they contract through cannibalism.<ref>{{cite journal |last1=Larsen |first1=Thor |last2=Kjos-Hanssen |first2=Bjørn |year=1983 |title=''Trichinella'' sp. in polar bears from Svalbard, in relation to hide length and age |volume=1 |issue=1 |pages=89–96 |doi=10.1111/j.1751-8369.1983.tb00734.x |journal=Polar Research|doi-broken-date=1 November 2024 |bibcode=1983PolRe...1...89L |s2cid=208525641 }}</ref>