What do polar bears eat?
Polar bears (Ursus maritimus) eat seal blubber almost exclusively. Ringed seals and bearded seals account for more than 90% of their annual calories. An adult bear needs about 2 kg of pure fat per day, equal to roughly 12,000 kcal, and kills 50 to 75 seals per year to stay alive.
A Carnivore Built Around One Food
The polar bear is the only member of the family Ursidae that the IUCN classifies as a marine mammal. It earned that classification through its food. Unlike the omnivorous brown bear, which eats salmon, grasses, berries, and roots in rough proportion, the polar bear has evolved into a near-obligate predator of a single taxonomic group: phocid ice seals.
Isotope analysis of bear tissue, stomach content studies dating back to the 1970s, and modern GPS-and-accelerometer fieldwork all converge on the same picture. More than nine of every ten calories a wild polar bear consumes comes from seal fat. Everything else the animal eats, from walrus calves to snow geese to dumpster scraps in Churchill, Manitoba, is a rounding error in the annual energy budget.
That dietary specialisation is the defining ecological fact of the species, and it is also the reason climate change threatens polar bear survival more than any other large carnivore on Earth. Take away the sea ice and you take away the seals.
"Polar bears are the most specialised of the eight bear species. They are, in essence, seal-eating machines, and every aspect of their ecology, behaviour, and physiology reflects that fact."
-- Ian Stirling, Polar Bears: The Natural History of a Threatened Species (2011)
The Two Seals That Matter
Ringed seal (Pusa hispida)
The ringed seal is the smallest and most abundant ice seal in the Arctic and the primary prey of polar bears across every one of the 19 recognised subpopulations. Adults weigh 50 to 70 kg. They maintain breathing holes through sea ice up to 2 m thick by scraping with their foreclaw claws, and they give birth to pups in snow-covered subnivean lairs between March and April.
That denning habit is a gift to polar bears. Pups are born with a white lanugo coat, weigh 4 to 5 kg, and double their body mass within six weeks on milk that is 45% fat. A bear that finds a birth lair can collapse the snow roof with a single forepaw strike and take a high-calorie meal that cannot run, swim, or dive.
Bearded seal (Erignathus barbatus)
Bearded seals are much larger, averaging 200 to 300 kg for adults, and they prefer drifting pack ice over broken landfast ice. They are the second staple in most polar bear diets and become disproportionately important for large adult males, who have both the size to subdue a bearded seal and the caloric demand to justify the effort. A mature bearded seal delivers 100+ kg of blubber in a single kill.
How the two species divide the menu
| Prey species | Typical share of diet | Seasonal peak | Blubber yield per adult |
|---|---|---|---|
| Ringed seal | 60 to 80% | March to July (pupping and weaning) | ~30 kg |
| Bearded seal | 10 to 25% | April to June | ~80 to 120 kg |
| Harp seal | 0 to 10% (regional) | Spring whelping patches | ~20 kg |
| Hooded seal | 0 to 5% (regional) | Drift ice | ~40 kg |
| Walrus (calves and weak adults) | <5% | Summer haul-outs | ~150 kg |
| Beluga carcass, narwhal carcass | <3% | Opportunistic | variable |
| Seabirds, eggs, small mammals | <2% | Summer ice-free | negligible |
| Terrestrial vegetation, berries, kelp | <1% | Late summer | negligible |
Percentages vary by subpopulation. Southern Beaufort bears consume more bearded seal than Western Hudson Bay bears, who rely almost entirely on ringed seal during their short spring hunting season.
The Three Hunting Methods
Polar bears catch seals in three ways, each adapted to a specific prey behaviour. The technique a bear uses on a given day depends on ice conditions, season, wind direction, and individual preference.
1. Still-hunting at breathing holes
Still-hunting is the default method and accounts for the majority of successful kills. A bear locates a seal breathing hole (called an aglu) by smell, often from more than a kilometre away, then settles motionless beside it. Seals must surface every 5 to 20 minutes to breathe. When the seal's nose touches the water surface inside the aglu, the bear strikes down with both forepaws and teeth, killing the seal and then dragging the 50+ kg carcass up through an opening often only 20 cm wide.
A still-hunting session can last anywhere from a few minutes to eight hours. Bears have been documented waiting beside a single breathing hole for an entire day without moving. Success rate is low in absolute terms -- somewhere between 2% and 10% of still-hunts end in a kill -- but the energy cost of waiting is also low, so the net energy yield is positive.
2. Stalk-hunting hauled-out seals
In late spring, when ringed seals and bearded seals haul out on the ice surface to bask, bears shift to stalking. A polar bear approaches a basking seal by swimming through leads, using ice blocks and pressure ridges as cover, then explodes across the last 10 to 20 m in a sprint. The bear must reach the seal before it slips back into its aglu, a window of about two to three seconds.
Stalking carries a higher success rate on naive or sleeping seals (15 to 30%) but demands far more energy than still-hunting, and it is strongly dependent on ice surface texture. Bears cannot cross open water silently, so a widening network of summer leads degrades stalking opportunities long before ice disappears entirely.
3. Subnivean birth-lair raiding
The third method is the most specialised and the most destructive to local seal populations. Between mid-March and late April, female ringed seals give birth in snow lairs dug above breathing holes. A polar bear walking over the ice can detect the lair by smell, rear up on its hind legs, and crash down through the 50 to 150 cm of compacted snow with enough force to pin the pup, the mother, or both.
Cubs of the year and subadults learn this technique from their mothers. It is the only hunting method that reliably kills multiple seals in a single event. In good ice years, adult females teaching yearling cubs have been recorded raiding five or more lairs in a single day.
"The birth lair hunt is unique in the mammalian world. There is no other large predator that excavates a subterranean nursery through compressed snow to reach neonates. It is a hunting technique that requires both the olfactory acuity of a bloodhound and the striking force of a grizzly."
-- Andrew Derocher, University of Alberta, in Polar Bears: A Complete Guide to Their Biology and Behavior (2012)
How Much Do Polar Bears Eat?
The 2 kg-per-day floor
A resting adult polar bear burns approximately 12,000 kcal per day. That baseline is considerably higher than the textbook value scaled from terrestrial carnivore allometry, because the polar bear lives in an environment that demands near-constant thermoregulation and because its body is built almost entirely of high-cost tissues: muscle, bone, and active fat rather than inert storage fat.
Twelve thousand kilocalories translates to roughly 2 kg of seal blubber, which carries about 9 kcal per gram once ingested and digested. That is the famous "2 kg of fat per day" figure you see cited in field guides, and it is the minimum maintenance requirement for a non-reproductive adult.
The active-hunter ceiling
USGS wildlife biologist Anthony Pagano and colleagues strapped GPS video collars and triaxial accelerometers onto nine free-ranging female bears in the Beaufort Sea in April 2014, 2015, and 2016. The study, published in Science in 2018, was the first to measure field metabolic rate in wild polar bears directly rather than inferring it from laboratory work on captive animals.
"On average, these bears needed to consume 1.6 times more energy than previously calculated. Four of the nine bears lost more than 10% of their body mass over the 8 to 11-day measurement period. One bear lost 18%."
-- Anthony Pagano et al., Science 359:568-572 (2018)
The corrected figure for an active hunting bear is closer to 19,000 kcal per day, or about 3.2 kg of blubber. For a pregnant female in late autumn building reserves for denning, the target can reach 55,000 kcal per day during hyperphagia.
Annual seal kill count
Working backward from field metabolic rate, body mass, and mean blubber content per seal kill, biologists estimate that a mature polar bear must kill 50 to 75 seals per year to maintain body condition. The lower bound applies to smaller subadult females hunting efficiently in good ice; the upper bound applies to large adult males and to reproductive females feeding cubs.
Caloric demand across life stages
| Life stage | Body mass | Daily kcal requirement | Annual seals required |
|---|---|---|---|
| Cub of the year (in den) | 10-12 kg | 0 (nursing on milk) | 0 (indirect via mother) |
| Yearling cub (out of den) | 40-80 kg | 4,000-6,000 | 15-20 (shared with mother) |
| Subadult female (3-5 yr) | 150-200 kg | 9,000-11,000 | 40-50 |
| Adult male | 400-680 kg | 12,000-19,000 | 55-75 |
| Pregnant female (hyperphagia) | 300-500 kg | up to 55,000 | 70+ (condensed into weeks) |
| Denning female (fasting) | falls 43% | 0 food, burns 1-1.5 kg fat/day | 0 |
| Lactating female (after emergence) | 150-250 kg | 15,000-25,000 | 60+ |
Why Seal Blubber Is the Only Food That Works
Energy density
Seal blubber is the most energy-dense tissue available to any Arctic predator. Pure adipose tissue from a ringed seal contains 8.8 to 9.2 kcal per gram, roughly twice the caloric density of skeletal muscle (4 kcal/g) and more than four times that of most fruits or vegetation (<2 kcal/g).
A polar bear feeding on a seal carcass will consume the blubber first, often stripping it cleanly away from the skin and leaving the carcass in a distinctive pattern biologists call "flensed" after the whaling term. Meat, viscera, and skin are secondary and are often abandoned once the bear is sated, with Arctic foxes, ravens, and glaucous gulls cleaning up the remains.
Fatty acid profile
Beyond raw caloric density, seal blubber carries a fatty-acid profile that polar bears have evolved to process in enormous quantities without metabolic damage. Wild polar bear blood cholesterol regularly exceeds 270 mg/dL. In a human that level would indicate severe cardiovascular disease. In polar bears, genomic analysis published by Rinker et al. (2019) identified positive selection on apolipoprotein B (APOB) and other lipid-handling genes, producing a metabolism that tolerates a diet that is 80 to 97% fat.
Water from fat
Polar bears rarely drink liquid water. They extract metabolic water from the oxidation of fat, which yields about 1.07 g of water per gram of fat metabolised. A bear processing 2 kg of blubber per day produces roughly 2 L of internally generated water, enough to maintain hydration without requiring open freshwater sources that are often unavailable on pack ice.
Secondary Prey and Carcass Scavenging
Seals are the staple, but polar bears are not strict obligate seal-eaters. They supplement their diet with a range of marine and terrestrial prey that becomes available under specific conditions.
Walrus
Adult walruses are too large and too dangerously armed for a polar bear to kill outright under most circumstances. Tusks 60 to 90 cm long and neck muscles thick enough to drive them through 10 cm of seal ice make an adult bull walrus a dangerous opponent. Bears instead target calves and sick or wounded adults hauled out at summer beach aggregations on Wrangel Island, Chukotka, and parts of Svalbard. When conditions force thousands of walruses ashore, a panicked stampede can kill calves outright, and polar bears routinely arrive to feed on the carcasses.
Beluga and narwhal
Polar bears have been documented killing belugas trapped in ice leads (sassats) where whales are confined to a small area of open water surrounded by closing ice. A bear can lie in ambush at the edge of the lead and strike as a beluga surfaces. Narwhal predation by polar bears is rarer but has been confirmed on Baffin Island and in north-east Greenland. Beached cetacean carcasses, particularly bowhead whale bone piles left by Inupiat subsistence hunters, attract concentrations of 30 to 60 bears per season in the western Beaufort.
Birds and eggs
During ice-free summers, bears have been observed raiding thick-billed murre, common eider, and snow goose colonies. A colony raid can destroy hundreds of nests in a morning but yields only a few hundred grams of egg mass per bear. Rockwell and Gormezano (2009) argued that goose-egg predation might partially offset fasting losses in Western Hudson Bay, a claim that subsequent caloric modelling has largely rejected.
Carrion
Polar bears scavenge whenever the opportunity arises. In Svalbard and the Canadian Arctic islands, reindeer carcasses left by avalanches, beached whales, hunter-shot polar bear carcasses, and even human garbage dumps at settlements such as Longyearbyen and Churchill contribute a measurable if minor share of summer calories to individual bears.
What Do Polar Bears Eat When There Is No Ice?
This is the question that now dominates Arctic ecology research, because in most of the polar bear's range, the ice-free season is expanding. Western Hudson Bay bears now spend an average of 30 days longer on land each summer than their grandparents' generation did in the 1980s. In the Southern Beaufort Sea, the equivalent figure is 21 days.
The summer fallback menu
When ice melts, bears come ashore. On land they have access to:
- Crowberries, bilberries, cloudberries, and bearberries growing on Arctic tundra
- Sedges, grasses, kelp, and seaweed along coastlines
- Lemmings, Arctic hare, and young ground-nesting birds
- Bird eggs, especially from goose and eider colonies
- Beached marine mammal carcasses
- Garbage and food waste near human settlements
Why the fallback cannot sustain the species
In 2009, Dyck and Kebreab published a caloric analysis of every terrestrial food item reported in polar bear stomach contents. Their conclusion was unequivocal: the land-based buffet cannot replace seals.
"To replace the fat content of a single adult ringed seal, a polar bear would need to consume approximately 16,000 crowberries, 216 snow goose eggs, or 1.5 adult caribou. The physiological and energetic costs of acquiring these foods exceed the caloric returns. Terrestrial foraging is not a realistic substitute for seal predation."
-- M. G. Dyck and E. Kebreab, Journal of Mammalogy 90:585-593 (2009)
A bear that relies on terrestrial foods during the ice-free season loses weight. How much weight depends on how much fat it brought ashore, how long ice-off lasts, and how much it moves. Western Hudson Bay bears now come ashore an average of 22 kg lighter than they did in the 1980s, and a further 1 kg per day on average during the fast.
"The Arctic sea ice ecosystem is collapsing, and with it the polar bear's food base. No amount of terrestrial foraging will save this species if the sea ice disappears. Polar bear conservation is, fundamentally, sea ice conservation."
-- IUCN/SSC Polar Bear Specialist Group, 19th meeting report (2021)
Cub Nursing: The Richest Milk in the Bear Family
Polar bear milk contains 31 to 33% fat, among the richest of any terrestrial mammal and roughly seven times the fat content of human milk. This fat content is a direct adaptation to maternal fasting during denning. A mother polar bear in her snow den cannot hunt and cannot eat. Every gram of milk she produces is built from her own body reserves, so evolution has selected for a milk chemistry that transfers the maximum amount of energy per unit volume.
Cubs are born weighing 500 to 700 grams and grow to 10 to 12 kg before emerging from the den in March or April. By the time they take their first steps in the outside world, they have already consumed roughly 20 kg of 32%-fat milk, which the mother manufactured entirely from her own stored blubber. For more on the biology of denning and early cub survival, see polar bear cubs: denning and survival.
A denning female loses up to 43% of her body weight between autumn den entry and spring emergence. A 300 kg pre-den female may emerge at 170 kg. She must then successfully hunt seals within weeks of leaving the den to replace lost reserves, because failing to do so threatens not just her own survival but her cubs', who depend on her milk for another 18 to 30 months.
The Polar Bear Food Chain
Polar bears sit at the apex of a short, fat-driven Arctic food chain. The chain is remarkable for how little biomass it contains at any given trophic level and for how completely it depends on sea ice as a physical platform.
- Phytoplankton and ice algae bloom under and on spring sea ice.
- Copepods and Arctic cod feed on the algae.
- Ringed and bearded seals feed on the fish and invertebrates.
- Polar bears feed almost exclusively on the seals.
- Arctic foxes, ravens, and gulls scavenge polar bear kill remains.
Persistent organic pollutants -- PCBs, DDT, brominated flame retardants -- enter the food web at the plankton level and biomagnify at each trophic step. By the time contaminants reach polar bear blubber, concentrations are often millions of times higher than in surrounding seawater. Female bears then off-load a portion of their accumulated contaminant burden into their cubs through the 32%-fat milk, which is why cubs of the year in the most contaminated subpopulations (East Greenland, Svalbard) show immune and endocrine abnormalities.
Feeding and Speed: Why Polar Bears Are Not Chase Predators
Unlike the cheetah or the wolf, the polar bear is not built for extended pursuit. Bears are sprinters and ambush hunters. A polar bear can run about 40 km/h on flat ice but cannot maintain that speed for more than a few hundred metres before overheating. The same bulk that stores the fat needed to survive between kills prevents the animal from chasing prey the way a predator adapted to open tundra or savanna could.
This constraint explains why polar bear hunting is overwhelmingly based on stealth, patience, and precisely timed single-strike attacks rather than pursuit. It also explains why a bear that misses its moment at a breathing hole often walks away without a second attempt, conserving energy for the next opportunity.
The food-driven predatory orientation of polar bears is also a public safety issue. Unlike grizzlies and black bears, which rarely treat humans as prey, polar bears occasionally do. See are polar bears dangerous to humans for the statistics and the circumstances under which attacks occur.
Seasonal Diet Shifts
Polar bear feeding ecology is strongly seasonal, reflecting ice dynamics and seal reproductive cycles.
January-February (late winter): Low hunting activity. Bears patrol landfast ice edges, still-hunting at breathing holes. Pregnant females remain in maternal dens, fasting. Caloric intake low, gradually drawing on fall reserves.
March-April (peak ringed seal pupping): The most important feeding window of the year. Bears exploit birth lairs and naive pups. A well-ice-connected bear can gain 1 to 2 kg per day during this period.
May-June (hauled-out seals and bearded seal pups): Stalk-hunting dominates. Bears target seals basking on the ice surface and bearded seal pups newly weaned on drift ice. Very high caloric yield.
July-August (ice retreat): Bears shift to summer behaviours. Western Hudson Bay, Baffin Bay, and Southern Beaufort bears come ashore. Ringed seals retreat to remaining pack ice. Hunting success plummets.
September-October (ice-free or minimal ice): Majority of bears onshore or on thin offshore ice. Terrestrial foods supplement but do not replace seal fat. Body mass declining across most subpopulations.
November-December (freeze-up): Bears return to new ice as soon as it forms. Renewed hunting effort. Pregnant females enter dens by late October or early November.
Comparing Polar Bear Diet to Other Bears
Polar bears stand alone among ursids in their dietary narrowness. For context:
- Brown bears are roughly 80 to 90% plant-based across most of their range, with meat, insects, and fish making up the remainder. Coastal populations on salmon rivers are an exception.
- Black bears are 75 to 85% plant-based, with meat largely from carrion and small mammals.
- Giant pandas are 99% bamboo specialists, but they are specialists in the opposite direction.
- Sun bears, spectacled bears, sloth bears are omnivores with preferences ranging from fruit to termites to tree nectar.
- Polar bears are roughly 90%+ seal blubber. No other bear species comes close to that level of carnivory.
This makes polar bears the most obligately carnivorous of the eight living bear species and one of the most dietarily specialised large predators on Earth, rivalled only by species like the snail kite or the Canada lynx.
Practical Implications for Conservation
Every dietary fact in this article is also a conservation fact. A polar bear that cannot reach seals cannot survive. A polar bear that cannot reach seals in March and April cannot store enough fat to survive summer. A female polar bear who cannot store enough fat cannot produce cubs, or produces cubs she cannot nurse to independence.
Sea ice extent in the Arctic has declined by about 13% per decade since satellite records began in 1979. Thickness has declined even more sharply. Multi-year ice, the thick, durable ice that once covered most of the Arctic Basin year-round, has been largely replaced by thinner, shorter-lived annual ice that breaks up earlier each summer and freezes later each autumn.
The polar bear's fat-intensive diet is not a lifestyle preference. It is a 500,000-year-old evolutionary commitment to a single ecological niche. When that niche shrinks, the species shrinks with it. Current global population is estimated at 22,000 to 31,000 animals across 19 subpopulations, of which four are already measurably declining and several more are projected to decline within two decades if current warming trajectories continue.
For more on the broader conservation picture, see why polar bears are endangered and the species hub page for Ursus maritimus.
Further Reading from Our Network
- For rigorous scientific writing and editing guidance, visit Evolang.
- For free intelligence and cognitive tests, try What's Your IQ.
- For music learning and auditory science, see When Notes Fly.
References
- Stirling, I. (2011). Polar Bears: The Natural History of a Threatened Species. Fitzhenry & Whiteside. https://doi.org/10.5860/CHOICE.49-2692
- Derocher, A. E. (2012). Polar Bears: A Complete Guide to Their Biology and Behavior. Johns Hopkins University Press. https://doi.org/10.56021/9781421403052
- Pagano, A. M., Durner, G. M., Rode, K. D., Atwood, T. C., Atkinson, S. N., Peacock, E., Costa, D. P., Owen, M. A., & Williams, T. M. (2018). High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear. Science, 359(6375), 568-572. https://doi.org/10.1126/science.aan8677
- Dyck, M. G., & Kebreab, E. (2009). Estimating the energetic contribution of polar bear summer diets to the total energy budget. Journal of Mammalogy, 90(3), 585-593. https://doi.org/10.1644/08-MAMM-A-103R2.1
- Rinker, D. C., Specian, N. K., Zhao, S., & Gibbons, J. G. (2019). Polar bear evolution is marked by rapid changes in gene copy number in response to dietary shift. PNAS, 116(27), 13446-13451. https://doi.org/10.1073/pnas.1901093116
- Rode, K. D., Regehr, E. V., Douglas, D. C., Durner, G., Derocher, A. E., Thiemann, G. W., & Budge, S. M. (2014). Variation in the response of an Arctic top predator experiencing habitat loss. Global Change Biology, 20(1), 76-88. https://doi.org/10.1111/gcb.12339
- Thiemann, G. W., Iverson, S. J., & Stirling, I. (2008). Polar bear diets and Arctic marine food webs: insights from fatty acid analysis. Ecological Monographs, 78(4), 591-613. https://doi.org/10.1890/07-1050.1
- Molnar, P. K., Bitz, C. M., Holland, M. M., Kay, J. E., Penk, S. R., & Amstrup, S. C. (2020). Fasting season length sets temporal limits for global polar bear persistence. Nature Climate Change, 10, 732-738. https://doi.org/10.1038/s41558-020-0818-9