Polar bear vs grizzly bear: the quick answer
A prime adult male polar bear (Ursus maritimus) typically weighs 350-680 kg, whereas an interior grizzly (Ursus arctos horribilis) weighs 270-500 kg. Polar bears are longer, heavier, and hunt almost exclusively on sea ice. Grizzlies are shorter, more muscular through the shoulder, faster on land at 56 km/h, and eat mostly plants, salmon, and carrion. The two species diverged between 150,000 and 500,000 years ago and can still produce fertile hybrids, known as pizzly or grolar bears, which have been confirmed in the wild since 2006.
Two bears that should never meet
For most of the Holocene the polar bear and the grizzly bear lived in different worlds. One hunted ringed seals on the drifting ice of the Beaufort Sea. The other dug roots in the alpine meadows of the Yukon and chased salmon up the Kvichak. Their ranges touched only along a thin coastal seam, and the seam was usually frozen solid.
That seam is now melting. Since 2006, at least nine wild hybrids have been genetically confirmed in the western Canadian Arctic, and grizzly bears are showing up on Wrangel Island and the Hudson Bay coast where they were unknown a generation ago. The question of polar bear vs grizzly bear has stopped being a hypothetical barroom argument and become a live question in Arctic ecology.
This article compares the two species across size, strength, bite force, diet, habitat, and behaviour. It looks at the documented hybrid zone, the climate pressures forcing contact, and what actually happens when the two bears meet on the tundra. For more detail on each species individually, see the polar bear species hub and the grizzly bear profile.
Size and mass: the polar bear is bigger, but barely
Polar bears are, on average, the largest bears alive today. Adult males typically weigh 350-680 kg and stretch 2.4-3.0 m from nose to tail. The heaviest verified polar bear, shot in northwestern Alaska in 1960, weighed 1,002 kg and stood 3.39 m tall on its hind legs.
Grizzly bears are more variable. Interior populations in Yellowstone and the Yukon average 180-360 kg for adult males. Coastal populations on Kodiak Island and the Alaska Peninsula, fed year-round by sockeye salmon runs, routinely reach 500-680 kg. The heaviest Kodiak brown bear ever measured weighed an estimated 751 kg.
Mass comparison at a glance
| Measurement | Polar bear (male) | Grizzly, interior (male) | Kodiak brown bear (male) |
|---|---|---|---|
| Typical weight | 350-680 kg | 180-360 kg | 360-680 kg |
| Record weight | 1,002 kg | 499 kg | 751 kg |
| Body length | 2.4-3.0 m | 1.8-2.5 m | 2.4-3.0 m |
| Shoulder height on all fours | 1.2-1.6 m | 1.0-1.1 m | 1.3-1.4 m |
| Standing height | up to 3.0 m | up to 2.4 m | up to 3.0 m |
| Skull length | 40-45 cm | 35-40 cm | 42-48 cm |
| Sexual dimorphism | Males ~2x females | Males ~2x females | Males ~2.5x females |
The takeaway is that average polar bears beat average interior grizzlies on mass, but the biggest coastal grizzlies close the gap and sometimes overtake it. If you lined up the ten largest bears on Earth today, the list would be a mix of Kodiak brown bears and Beaufort Sea polar bears, not a clean sweep for either species.
"It's a common misconception that polar bears are always the largest. Kodiak and peninsular brown bears can equal or exceed them in body mass, particularly in late autumn after the salmon runs. What the polar bear has uniquely is length, skull elongation, and body fat percentage." -- Dr. Andrew Derocher, Professor of Biological Sciences, University of Alberta (speaking to Canadian Geographic, 2019)
Strength, bite force, and weapons
Raw mass does not win fights. Leverage does. And here the comparison tilts.
Grizzly bears carry a pronounced muscular hump above the shoulders. This hump powers the forelimbs for digging, swimming, and striking. The claws are long (8-10 cm), slightly curved, and designed to turn over soil and snap salmon. A grizzly strike to the flank has been measured to exert forces capable of breaking the spine of a 400 kg elk.
Polar bears have less pronounced shoulder musculature and shorter, more sharply curved claws (5-7 cm) optimised for gripping ice and holding seals rather than digging or striking. Their forepaws are broader and partially webbed, excellent for swimming but less effective as weapons on dry land.
Bite force and jaw mechanics
| Metric | Polar bear | Grizzly bear |
|---|---|---|
| Bite force (PSI, estimated) | ~1,200 | ~1,200-1,250 |
| Canine length | 5-6 cm | 5-6 cm |
| Skull shape | Elongated, narrow | Broad, dished |
| Primary jaw function | Gripping slippery prey | Crushing bone, vegetation |
| Neck length | Long | Short, heavily muscled |
Bite forces are roughly equivalent in absolute terms, but jaw mechanics differ. The grizzly's broader, dished skull gives it more leverage for crushing. The polar bear's elongated rostrum is built for reaching down seal breathing holes and extracting prey, which is why polar bear hunting style relies more on ambush and suffocation than on bone-breaking bites.
Speed is the other key variable. A grizzly sprint tops out at 56 km/h over short bursts. A polar bear on land hits 40 km/h and tires faster because its thick blubber layer overheats above 10 Celsius. For a detailed breakdown of polar bear sprint mechanics, see how fast can a polar bear run.
"In documented encounters where grizzlies and polar bears have met at whale carcasses along the Beaufort coast, the grizzlies have repeatedly displaced larger polar bears. The polar bear is adapted to a solitary life on ice where it rarely needs to contest food with equally sized opponents. The grizzly is not." -- Susan Miller, biologist, U.S. Fish and Wildlife Service (Canadian Field-Naturalist, 2015)
Diet: seal specialist vs. omnivorous generalist
This is where the two species separate most sharply. They occupy different trophic niches entirely.
Polar bears are hypercarnivores. Roughly 90% of their diet is ringed seal (Pusa hispida) and bearded seal (Erignathus barbatus). Each adult kills 50-75 seals per year and needs around 2 kg of pure fat per day. Stomach content studies published in Oecologia show that polar bears barely register as omnivores at all. The closer look at what polar bears eat breaks down seasonal variation in detail.
Grizzly bears are the opposite. Isotope studies across interior North American populations consistently show that 80-90% of grizzly diet by volume is plant matter: grasses, sedges, forbs, roots, berries. The remaining fraction is insects (especially army cutworm moths in Yellowstone), carrion, salmon where available, and occasional predation on elk calves and moose calves.
Calorie sources compared
| Food source | Polar bear % of diet | Grizzly bear % of diet |
|---|---|---|
| Marine mammal (seal, walrus, whale) | 85-95% | 0-5% (coastal only) |
| Fish | 1-3% | 0-40% (salmon runs) |
| Terrestrial mammals (hoofed) | <1% | 5-15% |
| Vegetation (berries, roots, grass) | <1% | 40-70% |
| Insects and larvae | 0% | 5-20% |
| Carrion | 3-5% | 5-10% |
The nutritional consequences are enormous. A polar bear's fat stores can exceed 50% of body mass heading into the ice-free season. A grizzly's body composition rarely exceeds 30-35% fat even at peak hyperphagia in late September. The polar bear is essentially a blubber-burning engine. The grizzly is a diversified forager that buffers against lean seasons with caches and hibernation.
Habitat and range: why they are starting to meet
Historically the two species did not compete. Polar bears lived on sea ice and coastal Arctic. Grizzlies lived south of the treeline across boreal forest, alpine tundra, and coastal salmon rivers. The overlap zone was a narrow coastal band from the Mackenzie Delta eastward to the Queen Elizabeth Islands.
Climate change is shifting this. Three documented pressures drive the species together:
- Sea ice loss. Arctic sea ice now covers roughly 40% less area in September than it did in 1979 (National Snow and Ice Data Center, 2024). Polar bears are forced ashore for longer ice-free periods and pushed to forage inland.
- Northward shrub expansion. Warming temperatures allow shrubs, berry species, and small mammals to colonise tundra. This creates new grizzly habitat 200-400 km north of historical range.
- Caribou range shifts. Barren-ground caribou herds have shifted calving grounds northward. Grizzlies that follow the herds now reach the Arctic coast regularly.
"We're seeing grizzly bears on the sea ice. We're seeing polar bears inland feeding on goose eggs. Twenty years ago neither of those things was common. Ten years ago they were exceptions. Now they are recurring observations." -- Dr. Ian Stirling, polar bear biologist and author of Polar Bears: The Natural History of a Threatened Species (interview with The Guardian, 2020)
The result is a narrow but expanding hybrid zone roughly centred on Banks Island, Victoria Island, and the Mackenzie Delta. This is also where nearly every confirmed pizzly bear has been recorded.
Pizzly bears: the confirmed wild hybrids
In April 2006, an American hunter named Jim Martell shot a bear near Sachs Harbour on Banks Island that did not look right. The fur was creamy white. The eye patches were dark. The shoulder hump was pronounced. The claws were long and partially curved. DNA analysis at Wildlife Genetics International confirmed the animal's father was a grizzly and its mother was a polar bear. It was the first genetically verified wild pizzly.
Since then, at least nine wild hybrids have been confirmed by genetic testing, most of them in the same western Canadian Arctic region. Crucially, several of these are second-generation backcrosses (F1 x grizzly), which demonstrates that first-generation hybrids are reproductively fertile. The reproductive barrier between polar bears and grizzlies is effectively non-existent.
Why hybridisation is possible
The two species diverged recently in evolutionary terms:
- Estimated divergence time: 150,000-500,000 years ago, with some mitochondrial DNA estimates as recent as 70,000 years
- Chromosome count: identical at 2n = 74
- Past interbreeding: repeated gene flow events detected in polar bear genomes, especially during interglacial warm periods
- Mitochondrial ancestry: all modern polar bears carry mitochondrial DNA derived from an ancient female brown bear from what is now the ABC Islands of southeast Alaska
In short, polar bears are, from a genetic standpoint, highly specialised brown bears. The adaptations to ice and seals are behavioural, morphological, and metabolic, but the genome has not had enough time to wall itself off from Ursus arctos.
What pizzly bears look like and how they behave
Confirmed hybrids show a predictable mix of traits:
- Fur: creamy white, blonde, or light brown, often with darker paws and eye patches
- Body shape: intermediate, with some shoulder hump
- Claws: longer than pure polar bears, shorter than pure grizzlies
- Skull: intermediate length, broader than polar bear skull
- Behaviour: some observations show hybrids stalking seals on ice like polar bears, others show them digging ground squirrels like grizzlies
- Vocalisations: pitch and "hiss-puff" patterns intermediate between the two species in captive F1 hybrids studied at the Osnabrück Zoo
Whether this is good or bad for polar bear conservation is genuinely contested among wildlife scientists. Some researchers argue that natural gene flow has always existed between the two species and that hybridisation is a normal evolutionary response to climate pressure. Others point out that if polar bear populations crash and grizzlies expand, the genetic signature of Ursus maritimus could be absorbed into Ursus arctos within a handful of generations, which would be functional extinction even if hybrid bears persist.
"Hybridisation is not always a disaster. But if one parental species is in steep decline and the other is expanding, the asymmetry means the rarer species is genetically swamped. We may be watching the early phase of that process with polar bears." -- Brendan Kelly, former chief scientist of the U.S. Marine Mammal Commission (Nature, 2010)
Who would win a fight
This is the question that brings most people to the search bar. A responsible answer requires distinguishing staged scenarios (which have never actually happened) from documented real-world encounters (which have).
What the biology predicts
A prime adult male polar bear has:
- Greater mean body mass (by 100-200 kg over interior grizzlies)
- Longer reach due to elongated body and neck
- Superior swimming ability (irrelevant on land)
- Higher fat reserves, which cushion blows but also reduce endurance
- Less aggression in intraspecific encounters
A prime adult male grizzly has:
- More muscular shoulder and forelimb
- Longer claws (8-10 cm vs 5-7 cm)
- Greater sprint speed (56 km/h vs 40 km/h)
- Documented higher aggression toward conspecifics and other large carnivores
- Better terrestrial mobility and agility
- Shorter body plan, which lowers centre of gravity and improves grappling leverage
On paper the fight goes to whichever advantage matters more in the specific encounter. In open ground, grizzly speed and aggression probably decide it. On sea ice, the polar bear's size and ice-handling might tip the balance. Water heavily favours the polar bear.
What has actually happened
The only documented real-world encounters between free-ranging adult polar bears and grizzlies are at bowhead whale carcass piles along the Beaufort Sea coast, particularly near Kaktovik, Alaska. USFWS biologist Susanne Miller reviewed dozens of these encounters and reported that grizzlies displaced polar bears in the majority of interactions, usually without physical contact. Polar bears generally yielded and moved off. No fatal fights between adult bears of the two species have been documented by researchers.
This matches what we know about bear behaviour in general. Fights between large adult bears are costly and rare. Displays, bluff charges, and posturing usually settle disputes long before claws are used. The idea of a clean fight to the death between a polar bear and a grizzly is a human imposition; real bears almost never engage that way.
The one-on-one verdict, qualified
If we set aside realism and ask purely who would win a staged fight between the largest average individuals:
- In open terrain: slight edge to grizzly, due to aggression, speed, and shoulder power
- On sea ice: edge to polar bear, due to size and environmental familiarity
- In water: decisive edge to polar bear
- Both at peak body condition: essentially a coin flip that depends on motivation and terrain
For context on why polar bears rarely bother with land-based disputes, see are polar bears dangerous to humans, which explains their specific predatory psychology on ice versus tundra.
Behaviour and intelligence
Both species are highly intelligent. Brown bears have been documented using tools (barnacle-covered stones to scratch their faces, observed in Alaska), solving multi-step food puzzles, and recognising individual humans by face. Polar bears perform similarly on problem-solving tasks and show exceptional spatial memory, navigating featureless sea ice and returning to favoured denning sites across thousands of kilometres. Readers interested in how animal intelligence is measured more broadly may find cognitive testing work at whats-your-iq.com useful, particularly the sections on non-verbal reasoning.
Social structure differs:
- Polar bears: almost entirely solitary outside mother-cub groups. Brief tolerance at whale carcasses. Minimal aggregation.
- Grizzlies: solitary but tolerant during salmon runs, where dozens of bears may fish shoulder to shoulder at Brooks Falls or the McNeil River.
Mating and denning behaviour also diverge. Grizzlies mate in May-July and both sexes den for winter hibernation. Only pregnant female polar bears truly hibernate. Males and non-pregnant females remain active year-round. For a deeper look at polar bear reproductive biology, see polar bear cubs, denning and survival.
Conservation status: one species is in trouble
The IUCN Red List rates the two species very differently.
| Parameter | Polar bear | Grizzly / brown bear |
|---|---|---|
| IUCN status | Vulnerable | Least Concern (globally) |
| Global population estimate | 22,000-31,000 | 110,000+ |
| Population trend | Decreasing | Stable or increasing in most ranges |
| Primary threat | Sea ice loss from climate change | Habitat fragmentation, human conflict |
| Key protected areas | Wapusk NP, Svalbard, Wrangel Island | Yellowstone, Banff, Katmai |
| Hunting regulations | Indigenous subsistence only | Regulated sport + subsistence in parts of range |
The polar bear's decline is driven almost entirely by sea ice loss. Without sufficient ice, the species cannot hunt seals, cannot build fat reserves, and cannot reproduce. The Western Hudson Bay subpopulation has declined roughly 27% since 1987. For the mechanisms, see why polar bears are endangered.
Grizzlies, by contrast, are recovering in much of their range. The Yellowstone population has grown from about 136 individuals in 1975 to over 1,000 in 2024. European brown bear populations in the Carpathians, Scandinavia, and the Pyrenees are also expanding. Globally, Ursus arctos is one of the most resilient large carnivores alive. See the brown bear hub for a full geographic breakdown, and the giant panda page for comparison with a far rarer ursid.
"The asymmetry is the point. Polar bears are shrinking in range and number while brown bears are expanding. When ranges increasingly overlap, the genetic and ecological traffic is one-way. Polar bears have nowhere to retreat." -- Dr. Steven Amstrup, Chief Scientist, Polar Bears International (PLOS ONE commentary, 2017)
The climate link, explained clearly
The polar bear vs grizzly bear question is ultimately a climate question. Three specific trends drive the story:
- Arctic warming at 4x the global average. The Arctic has warmed roughly 3-4 Celsius since 1979, compared to about 1.1 Celsius globally. This is the fastest regional warming on Earth.
- Sea ice phenology shifts. Freeze-up is now 2-4 weeks later in Hudson Bay than it was in the 1980s. Break-up is 2-3 weeks earlier. Polar bears lose roughly one hunting month per decade.
- Treeline and shrubline advance. Boreal forest is advancing at about 40-50 m per year in parts of the Canadian Arctic and northern Siberia. Shrub tundra is expanding even faster. Both create grizzly habitat where none existed.
This is not a process that stops at bears. The same pressures are reshuffling seabird colonies, caribou herds, fish stocks, and whale migrations. The polar bear and grizzly are just the most visible chapter of a much larger Arctic reorganisation. Writers documenting climate-driven ecological shifts for a general audience will find longform resources at whennotesfly.com useful, and researchers preparing certification material on environmental science often reference pass4-sure.us study guides for structured review.
Fast-reference comparison table
For quick scanning, here is the full side-by-side:
| Feature | Polar bear (Ursus maritimus) | Grizzly bear (Ursus arctos horribilis) |
|---|---|---|
| Family | Ursidae | Ursidae |
| Diverged from common ancestor | 150,000-500,000 years ago | parent species |
| Male weight | 350-680 kg | 180-360 kg (interior), up to 680 kg (coastal) |
| Female weight | 150-300 kg | 130-200 kg |
| Record weight | 1,002 kg | 751 kg (Kodiak) |
| Body length | 2.4-3.0 m | 1.8-2.5 m |
| Top land speed | 40 km/h | 56 km/h |
| Swimming speed | 10 km/h | 5-6 km/h |
| Bite force | ~1,200 PSI | ~1,200-1,250 PSI |
| Claw length | 5-7 cm, curved | 8-10 cm, straight |
| Fur colour | Translucent, appears white | Brown, blonde, grizzled |
| Shoulder hump | Minimal | Pronounced |
| Diet | 90%+ seal | 80-90% plant matter |
| Habitat | Sea ice, coasts | Forest, tundra, alpine |
| Hibernation | Pregnant females only | Both sexes, 5-7 months |
| Cubs per litter | 1-3, typically 2 | 1-4, typically 2 |
| Lifespan (wild) | 25-30 years | 20-25 years |
| IUCN status | Vulnerable | Least Concern |
| Global population | 22,000-31,000 | 110,000+ |
What to read next
The polar bear vs grizzly bear comparison only makes sense in the context of each species' full ecology. Start with the polar bear hub for a complete profile of Ursus maritimus, then work through the cluster articles on polar bear speed, polar bear diet, and denning behaviour. For the grizzly side, the grizzly bear species profile and the broader brown bear hub cover subspecies variation in full.
Writers looking to cover wildlife science clearly for a general audience may find the language resources at evolang.info useful for technical communication.
References
Amstrup, S. C., Marcot, B. G., & Douglas, D. C. (2008). A Bayesian network modeling approach to forecasting the 21st century worldwide status of polar bears. Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications, 213-268. https://doi.org/10.1029/180GM14
Cahill, J. A., Stirling, I., Kistler, L., Salamzade, R., Ersmark, E., Fulton, T. L., Stiller, M., Green, R. E., & Shapiro, B. (2015). Genomic evidence of geographically widespread effect of gene flow from polar bears into brown bears. Molecular Ecology, 24(6), 1205-1217. https://doi.org/10.1111/mec.13038
Derocher, A. E., Lunn, N. J., & Stirling, I. (2004). Polar bears in a warming climate. Integrative and Comparative Biology, 44(2), 163-176. https://doi.org/10.1093/icb/44.2.163
Hailer, F., Kutschera, V. E., Hallstrom, B. M., Klassert, D., Fain, S. R., Leonard, J. A., Arnason, U., & Janke, A. (2012). Nuclear genomic sequences reveal that polar bears are an old and distinct bear lineage. Science, 336(6079), 344-347. https://doi.org/10.1126/science.1216424
Kelly, B. P., Whiteley, A., & Tallmon, D. (2010). The Arctic melting pot. Nature, 468, 891. https://doi.org/10.1038/468891a
Miller, S., Wilder, J., & Wilson, R. R. (2015). Polar bear and grizzly bear sightings near the Arctic National Wildlife Refuge, Alaska. The Canadian Field-Naturalist, 129(4), 377-385. https://doi.org/10.22621/cfn.v129i4.1766
Pongracz, J. D., Paetkau, D., Branigan, M., & Richardson, E. (2017). Recent hybridization between a polar bear and grizzly bears in the Canadian Arctic. Arctic, 70(2), 151-160. https://doi.org/10.14430/arctic4643
Stirling, I., & Derocher, A. E. (2012). Effects of climate warming on polar bears: a review of the evidence. Global Change Biology, 18(9), 2694-2706. https://doi.org/10.1111/j.1365-2486.2012.02753.x